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Janus
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Some of you may remember me from a ‘private’ tree growing site a few years back. I’m new to this site and am here for a very specific reason. Meanwhile, in the hope of getting my ban lifted on PM’s and posting in general I’m offering a large summary of my growing knowledge. It’s not comprehensive nor do I intend to stir any crap of other peoples styles. This is just what I believe to me true & works for me.
Below are about 15 pages of summary from some 100 pages of notes from a PhD consultant I hired a few years ago. I hired this person as I’d gotten tired of only marginal success growing MJ. There is much good information out there. However, books, journals, and def the web are full of bad information too. I’ve done my best to organize this and have only included what I think important. There are likely some redundancies and maybe some inconsistencies too. Anyway, there will be some controversy around additives, bloom enhancers, media, and h2o2. I don’t really want to debate anyone as I simply don’t have the time. Enjoy
Solution temps should ideally be matched to air temperatures - that is they should run about 7 to 9 degrees lower than the air temperatures with an optimum range for nutrient uptake of 68 - 75 F and always a little lower at night than during the day. Running 90 degree air and 68 solution will not make your plants happy. I run 70 degree solution and about 78 air.
Optimum humidity range is 70 - 85% for plant growth. Disease risk starts at around 88%. The humidity level range stays the same throughout the plants' life, expect in the cloning stage when a higher humidity levels prevent desiccation and excess water lost from the leaves at a time when there is no or little root system to take up water. So long as the humidity is below 85% (preferably 80% or below) during flowering this reduces the risk of disease infection – also good air movement up and under the plants during this time also helps prevent areas of higher humidity that might form. If you can handle the amount of water usage by the plants, then humidity in the lower end of the range 70 - 75% is the best level to run. Yes, I realize these ranges are way higher than most MJ growers run. I run in the 70% realm.
Too low RH is stressful on plants - if the air gets to dry, they will shut up the stomata in an attempt to slow the rate of water loss from their leaves and this slows photosynthesis which slows growth etc. You can't force a plant to increase transpiration too much, they will just shut up the stomata to prevent a high rate of water loss as they can only draw water up through the xylem from the roots at a certain rate. If the transport of water up the plant can't keep up with transpiration from the leaf, the stomata shut and that's why we have set points for RH around 60% minimum.
I grow trees indoors in a modified bucket system. 6 gallons for media (100% Big & Chunky Perlite) and a lower bucket/container for holding the top bucket). Plants are 5’ on center.
The roots in the second bucket are not as much of a concern as those up in the top bucket - at warmer temps, the physiology of roots changes from white and fluffy to thinner and browner, also as plant come into the bloom phase there will be some root die back as the plant diverts nutrients away from the production of new white roots up to the flower buds. Also the roots in the second bucket can run low on dissolved oxygen down and may die back (self prune back) a bit.
If the leaf temp measurements start to get a little higher than the air temperature then you know the plants have stopped transpiring and that needs to be avoided, as no growth will occur when the plants shut the stomata (photosynthesis will stop as well), which is why the infra red thermometer is a good tool to have on hand. A transpiring leaf will have a temperature just a little lower than the air. The transpiration has a cooling effect as water evaporates from the leaf. You can check to see if the plant is actively photosynthesising as well as being able to measure surface and nutrient temperatures around the growing area - it's a very useful tool to have, many growers don't know when their plants might be shutting down for whatever reason (high light can also cause this),
Tipburn and cupping are indicative of calcium uptake or deficiency problems - usually in hydroponics with a good quality nutrient, a deficiency of calcium in the nutrient is rare. So tipburn and cupping are likely to be a calcium uptake problem within the plant due to other causes, such as rapid growth and environmental interactions. Calcium uptake can sometime not keep up with new cell growth demand on a rapidly growing plant with an overly high or low rate of transpiration. High light, which pushes growth can sometimes bring on this effect, as can high EC, high temperatures etc. Summary: Most tipburn is actually a Calcium deficiency from too much P & K slowing the transport of C.
The main concern with algae is that it attracts fungus gnats and they carry disease and the larvae can chew on the root system
Ideally stock plants (mommas) need a good sized bucket as they are heavily reliant on a healthy, extensive root system to help regenerate after cuttings have been taken, and will be in the same bucket for a long time, however they will have pretty much the same requirements as the rest of the plants in terms of light intensity, humidity, temperature etc. However, if you are hand watering, then it's a good idea to go with a fairly moisture retentive media and larger bucket, so that they don't dry out between watering. Hand watering is a good method, as you need to cut back on irrigation after taking cuttings. However, if you are hand watering, then it's a good idea to go with a fairly moisture retentive media and larger bucket, so that they don't dry out between watering. Hand watering is a good method, as you need to cut back on irrigation after taking cuttings. Media such as coco fibre is good, however try to use a grade that has plenty of really long coarse fibres as well as the `fines' to help keep the growing mix open and allow air penetration. The feed schedule should be similar to the other plants in terms of EC and pH, however drop the EC and the amount of irrigation back after taking cuttings, this helps the plant during this time of stress, as soon as regeneration of the foliage is seen, make sure the EC is brought back up so that the quality of the new growth is not effected. A foliar spray once per week of the Spray-N-Grow is a good idea, especially when new foliage is developing. These plants would also benefit from some silica and fulvic in their nutrient. GH Eurogrowers with Diatomite is my preference for keeping mommas.
Use a razor blade to take cuttings - it limits the amount of cell damage to both the cutting and the stock plant and the less the cell damage, the better the recovery. If you get any shoot die back on the stock plant after cutting, then a mist with a fungicide might be needed, but usually the cuts heal quite quickly at the humidly levels you are running. Only take a maximum of one third of the stock plants total foliage when taking the cuttings, any more severely shocks the plant and it takes much longer to regenerate. Cut back on the watering and the nutrient EC by around one third just after cutting to allow rapid regeneration, but as soon as new foliage is seen bring these backup. If your cutting material is getting a bit thin, weak, stretched etc, then bring the EC up to harden it off before taking cuttings. Use the foliar spray once per week, use silica to strengthen the new foliage and fulvic to assist with nutrient uptake, especially in the week or so after taking cuttings.
Don't ever use LECA (Hydroton), it's probably not so bad in a mixture with another media, but on its own, trials have continually shown very poor growth, problems with iron retention, leaching of minerals and generally its not good stuff (hard to believe it is sold for hydroponic use). The coco on its own (provided its got some coarse and fine fibres is good) would be a good choice for hand watering, it holds plenty of moisture. There are some `coco chips' now on the market which would be a better choice for mixing with the finer coco media, rather than expanded clay.
Coir fibre needs to be avoided as well – samples we have seen on the US market vary considerably in terms of quality, some major brands have problems with Nitrogen draw down, calcium and phosphorus retention, high CEC, high sodium, massive amounts of potassium.
Additives: Bloom Enhancers are not always necessary. Modern Hydro nutes sometimes contain enough P & K. Even in bloom. Adding more causes imbalances of other essential nutrients. Blocking of Ca and Mg is common. However, after running nute samples to a lab for analysis I've determined, like most people, starting in about the first week of 12/12, P and K both need to be added in addition to the base nutes. This is not surprise to most MJ growers but there are some strains that simply don’t need the extra P & K. If you’re going to work the same strain for awhile and you can afford it, lab samples are the way to go. I determined my BK needs the P & K after having run the solution for 4 days with top offs of RO and Nutes daily. Out of an 80 gallon system I go through about 30 gallons per day at this point. And even tho the water was added daily and the EC level brought back to the target the ratio of P/K was too low at the end of the 4 days. I use Kool Bloom Dry and Liquid mostly as directed.
Base nutes (GH, CNS, etc), a fulvic acid and a silicate are all that are necessary.
Reapply additives when you do the complete nutrient change out. With additives there is always a risk of build up in recirculating systems and even quite safe ones can cause problems if such a build up occurred.
Fulvic acid is still in the class of `humic acids' which actually comprise a whole range of compounds, fulvic is the most biologically active form of humate and hence the best choice for hydroponics.
The best hole drill pattern in the new buckets is an even number of regularly spaced holes all over the base of the bucket – many smaller holes are better than 3 of 4 large holes as it allows more even draining over the entire base of the bucket and will prevent any `stagnant' areas where nutrient might pool and not drain way properly. Keep the holes just big enough to stop the perlite chunks from coming out – that should allow for good drainage, even when roots start to get down into that area
Fast nutrient flow rates zipping past a new and delicate root system which has just been transplanted into the perlite is not helpful and will retard the development of fine root hairs which is the reason, along with the fact that perlite spreads and retains nutrient quite well, for doing this. As the root system establishes and spreads and branches into the perlite the drippers can be shifted back and the flow rate increased to support the larger root surface area and higher requirement for oxygen, water and nutrients. You can start to increase the dripper rate as soon as you consider the plants have successfully established in the perlite and produced some good root outgrowth -normally this doesn't take that long. I would recommend that once you start to see the tops of the plant really start to shoot away and pickup growth, then the drippers start to be moved and the flow rate increased. I transplant my clones from aerocloners into the perlite and start with a steady but slow continuous stream of dual 1/4” lines. In a couple weeks once they’re established I turn the flow way down. Starting around week 4 of veg I start them on drippers. I slowing increase the drip rate throughout the plants life.
Dissolved oxygen (DO) levels are very important in this type of system -plants with roots contained in a small volume (compared to soil, even a 6 gal bucket is a limited root zone) are heavily dependent on both dissolved oxygen in the nutrient solution itself and that they can extract from the air in the pores between the perlite particles. All the oxygen the roots need is supplied as dissolved oxygen – either that which is directly dissolved in the nutrient flowing past the roots or that which diffuses from the air into the film of water that coats all the roots. Oxygen or lack of it in the root zone is actually something few growers understand and one that probably results in more yield reductions and plant deaths in hydroponic system than any other factor - growers should have a DO meter or test kit to check things are O.K. A continual flow of nutrient dripping through the media which brings fresh dissolved oxygen to the roots along with a very coarse media which is free draining and has large pore spaces for air to penetrate with fresh supplies of oxygen is good. However there are things that growers do to the nutrient that robs oxygen from the plant roots and that's one of the most common mistakes that can be made. Firstly - water or nutrient does not actually, even at full oxygen saturation, hold much dissolved oxygen, which is why in hydroponics it is so important to have lots of reoxygenation around the system. The amount of dissolved oxygen held by nutrient also depends on the temperature -the warmer the nutrient the less dissolved oxygen it can hold. So at around 10 C (50F) the average nutrient solution can hold at saturation around 13ppm of dissolved oxygen. At 30 C (86F) the amount that is held at saturation is only around 8 - 9 ppm of dissolved oxygen, which in parts per million really isn't much. The problem is further complicated by the fact that `saturation' levels need a really high rate of aeration to be obtained and most hydroponic system run at around 80%of what total saturation would be with an average of around 6 - 7ppm under warm cropping conditions. This is sufficient for plant growth -deficient oxygen levels for large, warm season plants in media are actually 2 - 3 ppm. The problem that can arise is that the nutrient is only holding at best 10ppm of dissolved oxygen under warm growing conditions, but the plant roots, of which there is a very large surface area of in a mature plant, are sucking up that oxygen at a rapid rate. The warmer the temperature and faster the rate of plant growth the faster is the rate of respiration in the root zone and the high is the oxygen demand in the root zone, so that plants are capable of stripping all the dissolved oxygen from the solution if its not being reoxygenated as its recirculated. Which is why having a DO meter is such a good idea, you can measure dissolved oxygen in the nutrient reservoir, or anywhere you can get the prone in, and check the oxygen levels. Anything over 5 ppm is acceptable at the temperatures you are running. The root system uses the oxygen in the process of respiration which goes on in roots 24/7 day and night, respiration is a process that uses oxygen to create energy to power root processes such as nutrient and water uptake. If the root system becomes deficient in oxygen, then rootcells start to rapidly die, the plant can't take up sufficient water and nutrients and will often wilt, develop chlorosis and the roots will go brown and rot - then the pathogens such as pythium can invade the damaged tissue and down the plants go. Many growers who claim a pathogen have infected the plant roots actually have damage that resulted from a lack of oxygen in the root system and the pathogen infection was secondary to that damage. There has been a huge increase in growers reporting this and I suspect it has a lot to do with the use of many of the `organic' additives on the market these days. When organic additives or organic matter which contains organic carbon is added into a hydroponic nutrient solution it has a direct effect on oxygen levels. The organic carbon is a food source for microbes which naturally live in all hydroponic systems and don't usually cause any harm (beneficial in fact), when large amounts of carbon are available in the nutrient as a food source the microbes feed on this, multiply,(double in population numbers very 20 mins in warm conditions) and as this goes on they use up vast amounts of the dissolved oxygen in the system. At the rate of multiplication of microbes it only takes a few hours in most cases before they have significantly increased the BOD (Biological oxygen demand) of the system to the point where there is not enough oxygen left over for the plant roots. At this point the nutrient goes `anaerobic' meaning no oxygen and often there are bad smells or slime or fur growing in or on the nutrient which further produces toxics which can damage the plant roots and whole thing just goes bad. Very small amounts of organic product can usually be tolerated in a well aerated nutrient solution as the microbes use all the carbon that it provides then when there is no more they die off and stop the loss of any more oxygen. But large amounts or use of a number of different organic additives will de-oxygenate the root zone. Organic compounds include sugars, amino acids, vitamins, enzymes, guano extracts, seaweed and compost extracts etc all of which are great food sources for microbes in solution. Also be wary of those products on the market that are sold for boosting dissolved oxygen in nutrient solutions - most are just bottled hydrogen peroxide or calcium peroxide powder and will oxidise/damage roots (that's a whole other rather long and complex explanation).
Many growers who claim a pathogen has infected the plant roots actually have damage that resulted from a lack of oxygen in the root system and the pathogen infection was secondary to that damage. There has been a huge increase in growers reporting this and I suspect it has a lot to do with the use of many of the `organic' additives on the market these days. When organic additives or organic matter which contains organic carbon is added into a hydroponic nutrient solution it has a direct effect on oxygen levels. The organic carbon is a food source for microbes which naturally live in all hydroponic systems and don't usually cause any harm (beneficial in fact), when large amounts of carbon are available in the nutrient as a food source the microbes feed on this, multiply,(double in population numbers very 20 mins in warm conditions) and as this goes on they use up vast amounts of the dissolved oxygen in the system. At the rate of multiplication of microbes it only takes a few hours in most cases before they have significantly increased the BOD
(Biological oxygen demand) of the system to the point where there is not enough oxygen left over for the plant roots. At this point the nutrient goes `anaerobic' meaning no oxygen and often there are bad smells or slime or fur growing in or on the nutrient which further produces toxics which can damage the plant roots and whole thing just goes bad. Very small amounts of organic product can usually be tolerated in a well aerated nutrient solution as the microbes use all the carbon that it provides then when there is no more they die off and stop the loss of any more oxygen. But large amounts or use of a number of different organic additives will de oxygenate the root zone. So just as a caution- I am aware of the large number of `organic' type additives sold on the hydroponic market as `amazing' plant boosting etc etc nutrient additives, but be very wary of these (organic compounds include sugars, amino acids, vitamins, enzymes, guano extracts, seaweed and compost extracts etc all of which are great food sources for microbes in solution). Also be wary of those products on the market that are sold for boosting dissolved oxygen in nutrient solutions - most are just bottled hydrogen peroxide or calcium peroxide powder and will oxidise/damage roots (that's a whole other rather long and complex explanation). I NEVER use any organic or carbon based compounds in my solution. I’ve seen the solution go anaerobic and it’s quite destructive. I got tired of pontificating DO levels and long ago purchase a meter to know definitively what was happening in my solution.
Root pruning should also be avoided - any time you cut or damage the roots there is a significant increase in the risk of root rot pathogen infection. Many pathogens can't actually attack a healthy and intact root, but if it is cut, then entry is easy and infection can be rapid as roots are in a very damp, moist environment, perfect for infection by fungi and bacteria. Also it serves no physiological purpose unless you are growing `bonsai' trees - root pruning can be used to stunt the plant and restrict the growth and development of the top of the plant which can be used in decorative ornamental trees such as bonsai, but usually we don't want to restrict or delay growth of cropping plants. Also it severely stresses the plant by restricting water and nutrient uptake, so leaving the roots alone is best.
Root systems in plants generally are in proportion to the size of the top of the plant and slightly dependent on species. As the top of the plant increases in size, the root system also grows in proportion, the reason being that it's the surface area of root that is important to be able to take up sufficient water and nutrients in times of high demand to support the size of the top of the plant. A large plant with a small root system, even a very healthy and efficient root system is very uncommon; typically the size of the root system is always in proportion to the top of the plant. If its not, then we would expect there is a problem in the root zone such as lack of oxygen, nutrient imbalance ,high EC, incorrect pH, moisture stress etc and this then restricts growth of the upper portion of the plant. In soil, if water or nutrients are limited you often see very long tap roots developing which grow down in search of water, but in hydroponics this does not occur, although growing hydroponically does not mean that the roots don't need to be large and extensive. There is bit of myth about hydroponics that root systems can remain rather small as they have all the water and nutrients delivered to them, but that's not really the case, large plants in particular need that large surface area of root tissue to be able to absorb sufficient water and nutrients (large volumes) and do that they need an extensive root system. I’ve found that 6 gallon buckets along with the 100% perlite I get fantastic and fuzzy white root development. When the plant is in peak consumption phase (about 4 weeks per run) I’ll go through 3.5 to 4.0 gallons per plant.
When plants go into a rapid reproductive phase and there are flowers/buds/seeds/fruit etc being produced the growth of the root system slows because the plant will direct assimilate into those reproductive parts at the expense of the roots. In some plants, like a heavily fruiting tomato for example this gets so extreme that roots even die back a little at this time as the plant just doesn't give priority to new root growth and regeneration when all its reserves and energy are going into fruit production.
Spray N Grow as a foliar has been extensively and widely tested in both field agriculture and hydroponics
Stay on the veg formula for at least 1 week after switching to 12 hours. By not changing the formulation during this stage, when the plants are going through an adaptation to the new lighting regime, it reduces the level of stress and helps maintain the rate of vegetative growth. After 1 week the plants should be fully adapted to the new lighting conditions and changes to the formulation can then be made. Bloom formulations don't actually speed up the rate of flowering or induce flowering in any way (day length and plant maturity does that), what they do is provide a different ratio of nutrients that the plant requires when going into the reproductive phase. So all that a bloom formulation does is provide the new ratio of nutrients that the plants need once they start flower growth and development, this helps the solution stay in balance longer and prevents depletion of elements such as potassium and phosphorus.
Plants need time to adapt to increases in light and this takes days rather than hours, probably only increase the light once every 7 days, allow the plants to adapt then increase again in another 7 days and always check of signs of high light damage each time (bleaching of foliage, yellowing, drying off of the edges, thickened leaves etc). I do my light increase in 5 to 6 day increments.
Day temp of 75 - 80 is optimal for ambient and low levels of co2 enrichment, once you get past around 450 - 500ppm run the temps a little higher 78 - 84 F. Plants can make far greater use of the additional CO2 if the temps are warmer - both temperature and CO2 are what power photosynthesis so increasing one without the other doesn't give the best increase in photosynthesis possible (watch out for a faster rate of water uptake then this is done). Generally the temps would be run at the lower end of this range during that early veg phase as it helps the plant establish faster and puts less stress on the root system, and at the higher end when going into the flowering phase when you might be boosting the light and CO2 the most. Temps when the lights are off need to be a little cooler 71 - 75F, although warmer night temps won't actually harm the plant, the plants are still respiring at night - respiration is a process that uses up oxygen and release CO2 and it is essential for plant processes, however respiration also uses up plant reserves (assimilate that was produced during the light hours) and the rate of respiration increases dramatically with temperature, so we don't want the plants respiring a whole lot of their stored assimilate during the night. Also a slightly lower night temperature has beneficial physiological effects in flowering plants.
CO2 is toxic and levels of over 2000ppm can be very destructive.
Generally if CO2 is running a bit too high then the plant reacts by initially shutting down photosynthesis (i.e the stomata close in an attempt to protect the plant from toxicity), this prevents the plant from transpiring, even if the humidity levels are fine etc. So the plants may look as if they are starving, losing their green color as chloroplasts are destroyed and no photosynthesis can take place. If the levels are way too high (like over 1600ppm), then a phytotoxicity develops which usually results in rolled, thickened deformed leaves, that may twist and look dark. Young plants are more sensitive to CO2 than older ones. Co2 burners can produce toxic by-products and ethylene if incomplete combustions occurs and this causes significant plant damage (many commercial growers have experienced this). Increasing CO2 will also increase the rate of water uptake and use by the plant as they carry out a higher rate of photosynthesis. Co2 levels of 900 to 1,000ppm, once the plant has adapted to the increases, is best. I’ve seen several Co2 burners produce mystery by-products over the years and have suffered much grief. Now, tho a huge PIA I choose to run bottles instead. (Max of 1,000ppm)
Chloramines are becoming more common in town supply water. It is toxic to plants. Problems usually take around 10 days from damage to symptoms showing up. Plant in dirt are less susceptible to chloramine because of the soils buffering capacity. RO water only for my plant.
UV sterilization of the nutrient solution is not a good idea - it tends to interact with iron chelate in the nutrient solution, making it unavailable for plant uptake and resulting in iron deficiency. UV does have a high kill rate for pathogens, but the problems with iron chelate mean that the grower has to monitor iron levels in solution and adjust accordingly on a regular basis; even then iron deficiency can be a common problem. Some commercial growers do use UV sterilisation for pathogen control in recirculating systems, but when they do so they switch to using different forms of iron chelate such as Fe-EDDHA in their nutrient formulation which are more stable under UV sterilization and they also carry out regular iron chelate testing. That's probably not practical when using a nutrient premix such as GH or any of the others
Large lava chunks is sort of like a vertical NFT with nutrient cascading down the rock particles 24/7, which is O.K, but the plant will put energy into growing roots directly downwards, following the flow of nutrient rather then producing a highly branched root system that fills out the whole bucket with roots. Also there are likely to be pores inside the rock that pathogens, and old root material might accumulate in, creating a disease risk and it can be hard to disinfect media with that sort of porous structure. Lava is way left over from the 'old days'. I haven't touched the stuff in years.
Fluffy white root hairs which will maximize the surface area of the root and hence nutrient and water uptake. We never get these types of roots in lava. Perlite has great root development.
Keeping the EC stable is important - letting the nutrient dilute creates a situation of continually changing osmotic potential in the root zone and can create a bit of osmotic shock if allowed to dilute to much and then the EC is suddenly increased. Plants need a little time to adjust to changes in EC, so just adjusting the EC back each day gives a small change in EC rather than a large one. You would notice that as the EC diluted the plants took up more water, which is just an effect of the lower of the osmotic potential in the root zone.
H2O2 will oxidize completely if there is sufficient `organic' matter in the system for it to work on, oxidize and then deactivate. If you have a clean system, it has nothing to work on and hence won't deactivate and can attack roots instead if there is a build up.
As a last resort `Captan WG' (note it has to be the WG formulation) can be used for root rot and damping off (Pythium) pathogens, but don't use it `just in case' and if you can always trail these things in one system at a dilute rate first to see if there is any adverse reaction.
H2O2 is a powerful oxidant, it will oxidize organic matter in the system/nutrient, however the rate needed to kill fungal spores on average is at least 100 - 120ppm, more for persistent spores, up to200ppm and a contact time of 20 mins. However, we know that rates ofH2O2 as low as 6ppm will damage seedling roots, particularly in clean systems where the active H2O2 has no other organic matter to work on. I think your more mature plants would not have been badly affected by this, but the rate was high enough to have a negative effect on young plants in a clean system. H2O2 works by oxidizing all organic matter, including live root systems- live roots are a little more resistant to oxidation than dead root material, or spores, but can still be damaged. H2O2 damaged roots tend to brown off and go mushy, so the damage looks a lot like the pathogen growers are trying to kill off with the H2O2 in the first place. What we have seen with cucumber crops is that while the plant doesn't die off, they still look healthy; they ended up being about 20% shorter and about 2 weeks delayed when H2O2 was used in the nutrient at low rates.
Since you would have to add 10 times the dose you used to actually kill off any pathogen spores and since that would certainly burn back a lot of roots, its best to just not use it. H2O2 is fine to use for cleaning up your equipment and system between crops (use at least 300ppm to do so), but rinse really well with water to remove residues before replanting.
RO flush, if necessary, just long enough to get a few good rinses through, no more than 2 hours even if you have to manually rinse the media. Plain water won't kill the plants - when plants which have been in nutrient solution of a given strength then receive just water or lower strength solution the osmotic potential actually drops so that the plants can take up more water, faster. If the EC is increased in strength rapidly and high EC levels are then run, then the osmotic potential increases and the plant root cells actually loose water back into the nutrient solution and dehydrate somewhat. I flush my media thoroughly every 7 days.
High EC. Using really ‘aggressive’ strength EC levels doesn't give faster growth and more nutrient uptake but can actually stress plants as they struggle to take up water. On the other hand using high EC promotes shorter, more compact growth, increased flavour in fruit etc. So giving the plants a couple of hours of plain water is not really long enough to cause any major effects on plant growth, but the lower EC after that allows them to take up water and nutrients easier in their current state of health and might get them back feeding again. This is a standard commercial practice for plants that seem to have stopped growing or taking up nutrients in are circulating system - kinda like a `detox' for plants that will kick start them back into growth by getting rid of any build up, but it has to be good quality water and no `flushing products'.
Potassium levels are kept up with the use of the potassium hydroxide and potassium silicate and even accumulates a little and can end up accumulating with insufficient nitrogen in the ratio of elements(and possibility insufficient calcium as well).
In GH nutes there is around 4 - 5% NH4 form of nitrogen - this is what gives it `pH buffering capacity' that is it keep the pH down when the plants are taking up ions from solution. However the faster the plants are growing and taking out nutrients, the faster the pH comes down and it seems to run on the low side.
In the end of all that I have a system, protocol, and knowledge base that works for me. I can consistently pull down round after healthy round and that’s good enough for me.
Peace
Below is what my lower bkts look like. However, the plumbing has changed some. I no longer have 2" of DWC and air. The drain is directly on the bottom of these containers and the air has been removed. My reservoirs are heavily aerated tho.
Below are about 15 pages of summary from some 100 pages of notes from a PhD consultant I hired a few years ago. I hired this person as I’d gotten tired of only marginal success growing MJ. There is much good information out there. However, books, journals, and def the web are full of bad information too. I’ve done my best to organize this and have only included what I think important. There are likely some redundancies and maybe some inconsistencies too. Anyway, there will be some controversy around additives, bloom enhancers, media, and h2o2. I don’t really want to debate anyone as I simply don’t have the time. Enjoy
Solution temps should ideally be matched to air temperatures - that is they should run about 7 to 9 degrees lower than the air temperatures with an optimum range for nutrient uptake of 68 - 75 F and always a little lower at night than during the day. Running 90 degree air and 68 solution will not make your plants happy. I run 70 degree solution and about 78 air.
Optimum humidity range is 70 - 85% for plant growth. Disease risk starts at around 88%. The humidity level range stays the same throughout the plants' life, expect in the cloning stage when a higher humidity levels prevent desiccation and excess water lost from the leaves at a time when there is no or little root system to take up water. So long as the humidity is below 85% (preferably 80% or below) during flowering this reduces the risk of disease infection – also good air movement up and under the plants during this time also helps prevent areas of higher humidity that might form. If you can handle the amount of water usage by the plants, then humidity in the lower end of the range 70 - 75% is the best level to run. Yes, I realize these ranges are way higher than most MJ growers run. I run in the 70% realm.
Too low RH is stressful on plants - if the air gets to dry, they will shut up the stomata in an attempt to slow the rate of water loss from their leaves and this slows photosynthesis which slows growth etc. You can't force a plant to increase transpiration too much, they will just shut up the stomata to prevent a high rate of water loss as they can only draw water up through the xylem from the roots at a certain rate. If the transport of water up the plant can't keep up with transpiration from the leaf, the stomata shut and that's why we have set points for RH around 60% minimum.
I grow trees indoors in a modified bucket system. 6 gallons for media (100% Big & Chunky Perlite) and a lower bucket/container for holding the top bucket). Plants are 5’ on center.
The roots in the second bucket are not as much of a concern as those up in the top bucket - at warmer temps, the physiology of roots changes from white and fluffy to thinner and browner, also as plant come into the bloom phase there will be some root die back as the plant diverts nutrients away from the production of new white roots up to the flower buds. Also the roots in the second bucket can run low on dissolved oxygen down and may die back (self prune back) a bit.
If the leaf temp measurements start to get a little higher than the air temperature then you know the plants have stopped transpiring and that needs to be avoided, as no growth will occur when the plants shut the stomata (photosynthesis will stop as well), which is why the infra red thermometer is a good tool to have on hand. A transpiring leaf will have a temperature just a little lower than the air. The transpiration has a cooling effect as water evaporates from the leaf. You can check to see if the plant is actively photosynthesising as well as being able to measure surface and nutrient temperatures around the growing area - it's a very useful tool to have, many growers don't know when their plants might be shutting down for whatever reason (high light can also cause this),
Tipburn and cupping are indicative of calcium uptake or deficiency problems - usually in hydroponics with a good quality nutrient, a deficiency of calcium in the nutrient is rare. So tipburn and cupping are likely to be a calcium uptake problem within the plant due to other causes, such as rapid growth and environmental interactions. Calcium uptake can sometime not keep up with new cell growth demand on a rapidly growing plant with an overly high or low rate of transpiration. High light, which pushes growth can sometimes bring on this effect, as can high EC, high temperatures etc. Summary: Most tipburn is actually a Calcium deficiency from too much P & K slowing the transport of C.
The main concern with algae is that it attracts fungus gnats and they carry disease and the larvae can chew on the root system
Ideally stock plants (mommas) need a good sized bucket as they are heavily reliant on a healthy, extensive root system to help regenerate after cuttings have been taken, and will be in the same bucket for a long time, however they will have pretty much the same requirements as the rest of the plants in terms of light intensity, humidity, temperature etc. However, if you are hand watering, then it's a good idea to go with a fairly moisture retentive media and larger bucket, so that they don't dry out between watering. Hand watering is a good method, as you need to cut back on irrigation after taking cuttings. However, if you are hand watering, then it's a good idea to go with a fairly moisture retentive media and larger bucket, so that they don't dry out between watering. Hand watering is a good method, as you need to cut back on irrigation after taking cuttings. Media such as coco fibre is good, however try to use a grade that has plenty of really long coarse fibres as well as the `fines' to help keep the growing mix open and allow air penetration. The feed schedule should be similar to the other plants in terms of EC and pH, however drop the EC and the amount of irrigation back after taking cuttings, this helps the plant during this time of stress, as soon as regeneration of the foliage is seen, make sure the EC is brought back up so that the quality of the new growth is not effected. A foliar spray once per week of the Spray-N-Grow is a good idea, especially when new foliage is developing. These plants would also benefit from some silica and fulvic in their nutrient. GH Eurogrowers with Diatomite is my preference for keeping mommas.
Use a razor blade to take cuttings - it limits the amount of cell damage to both the cutting and the stock plant and the less the cell damage, the better the recovery. If you get any shoot die back on the stock plant after cutting, then a mist with a fungicide might be needed, but usually the cuts heal quite quickly at the humidly levels you are running. Only take a maximum of one third of the stock plants total foliage when taking the cuttings, any more severely shocks the plant and it takes much longer to regenerate. Cut back on the watering and the nutrient EC by around one third just after cutting to allow rapid regeneration, but as soon as new foliage is seen bring these backup. If your cutting material is getting a bit thin, weak, stretched etc, then bring the EC up to harden it off before taking cuttings. Use the foliar spray once per week, use silica to strengthen the new foliage and fulvic to assist with nutrient uptake, especially in the week or so after taking cuttings.
Don't ever use LECA (Hydroton), it's probably not so bad in a mixture with another media, but on its own, trials have continually shown very poor growth, problems with iron retention, leaching of minerals and generally its not good stuff (hard to believe it is sold for hydroponic use). The coco on its own (provided its got some coarse and fine fibres is good) would be a good choice for hand watering, it holds plenty of moisture. There are some `coco chips' now on the market which would be a better choice for mixing with the finer coco media, rather than expanded clay.
Coir fibre needs to be avoided as well – samples we have seen on the US market vary considerably in terms of quality, some major brands have problems with Nitrogen draw down, calcium and phosphorus retention, high CEC, high sodium, massive amounts of potassium.
Additives: Bloom Enhancers are not always necessary. Modern Hydro nutes sometimes contain enough P & K. Even in bloom. Adding more causes imbalances of other essential nutrients. Blocking of Ca and Mg is common. However, after running nute samples to a lab for analysis I've determined, like most people, starting in about the first week of 12/12, P and K both need to be added in addition to the base nutes. This is not surprise to most MJ growers but there are some strains that simply don’t need the extra P & K. If you’re going to work the same strain for awhile and you can afford it, lab samples are the way to go. I determined my BK needs the P & K after having run the solution for 4 days with top offs of RO and Nutes daily. Out of an 80 gallon system I go through about 30 gallons per day at this point. And even tho the water was added daily and the EC level brought back to the target the ratio of P/K was too low at the end of the 4 days. I use Kool Bloom Dry and Liquid mostly as directed.
Base nutes (GH, CNS, etc), a fulvic acid and a silicate are all that are necessary.
Reapply additives when you do the complete nutrient change out. With additives there is always a risk of build up in recirculating systems and even quite safe ones can cause problems if such a build up occurred.
Fulvic acid is still in the class of `humic acids' which actually comprise a whole range of compounds, fulvic is the most biologically active form of humate and hence the best choice for hydroponics.
The best hole drill pattern in the new buckets is an even number of regularly spaced holes all over the base of the bucket – many smaller holes are better than 3 of 4 large holes as it allows more even draining over the entire base of the bucket and will prevent any `stagnant' areas where nutrient might pool and not drain way properly. Keep the holes just big enough to stop the perlite chunks from coming out – that should allow for good drainage, even when roots start to get down into that area
Fast nutrient flow rates zipping past a new and delicate root system which has just been transplanted into the perlite is not helpful and will retard the development of fine root hairs which is the reason, along with the fact that perlite spreads and retains nutrient quite well, for doing this. As the root system establishes and spreads and branches into the perlite the drippers can be shifted back and the flow rate increased to support the larger root surface area and higher requirement for oxygen, water and nutrients. You can start to increase the dripper rate as soon as you consider the plants have successfully established in the perlite and produced some good root outgrowth -normally this doesn't take that long. I would recommend that once you start to see the tops of the plant really start to shoot away and pickup growth, then the drippers start to be moved and the flow rate increased. I transplant my clones from aerocloners into the perlite and start with a steady but slow continuous stream of dual 1/4” lines. In a couple weeks once they’re established I turn the flow way down. Starting around week 4 of veg I start them on drippers. I slowing increase the drip rate throughout the plants life.
Dissolved oxygen (DO) levels are very important in this type of system -plants with roots contained in a small volume (compared to soil, even a 6 gal bucket is a limited root zone) are heavily dependent on both dissolved oxygen in the nutrient solution itself and that they can extract from the air in the pores between the perlite particles. All the oxygen the roots need is supplied as dissolved oxygen – either that which is directly dissolved in the nutrient flowing past the roots or that which diffuses from the air into the film of water that coats all the roots. Oxygen or lack of it in the root zone is actually something few growers understand and one that probably results in more yield reductions and plant deaths in hydroponic system than any other factor - growers should have a DO meter or test kit to check things are O.K. A continual flow of nutrient dripping through the media which brings fresh dissolved oxygen to the roots along with a very coarse media which is free draining and has large pore spaces for air to penetrate with fresh supplies of oxygen is good. However there are things that growers do to the nutrient that robs oxygen from the plant roots and that's one of the most common mistakes that can be made. Firstly - water or nutrient does not actually, even at full oxygen saturation, hold much dissolved oxygen, which is why in hydroponics it is so important to have lots of reoxygenation around the system. The amount of dissolved oxygen held by nutrient also depends on the temperature -the warmer the nutrient the less dissolved oxygen it can hold. So at around 10 C (50F) the average nutrient solution can hold at saturation around 13ppm of dissolved oxygen. At 30 C (86F) the amount that is held at saturation is only around 8 - 9 ppm of dissolved oxygen, which in parts per million really isn't much. The problem is further complicated by the fact that `saturation' levels need a really high rate of aeration to be obtained and most hydroponic system run at around 80%of what total saturation would be with an average of around 6 - 7ppm under warm cropping conditions. This is sufficient for plant growth -deficient oxygen levels for large, warm season plants in media are actually 2 - 3 ppm. The problem that can arise is that the nutrient is only holding at best 10ppm of dissolved oxygen under warm growing conditions, but the plant roots, of which there is a very large surface area of in a mature plant, are sucking up that oxygen at a rapid rate. The warmer the temperature and faster the rate of plant growth the faster is the rate of respiration in the root zone and the high is the oxygen demand in the root zone, so that plants are capable of stripping all the dissolved oxygen from the solution if its not being reoxygenated as its recirculated. Which is why having a DO meter is such a good idea, you can measure dissolved oxygen in the nutrient reservoir, or anywhere you can get the prone in, and check the oxygen levels. Anything over 5 ppm is acceptable at the temperatures you are running. The root system uses the oxygen in the process of respiration which goes on in roots 24/7 day and night, respiration is a process that uses oxygen to create energy to power root processes such as nutrient and water uptake. If the root system becomes deficient in oxygen, then rootcells start to rapidly die, the plant can't take up sufficient water and nutrients and will often wilt, develop chlorosis and the roots will go brown and rot - then the pathogens such as pythium can invade the damaged tissue and down the plants go. Many growers who claim a pathogen have infected the plant roots actually have damage that resulted from a lack of oxygen in the root system and the pathogen infection was secondary to that damage. There has been a huge increase in growers reporting this and I suspect it has a lot to do with the use of many of the `organic' additives on the market these days. When organic additives or organic matter which contains organic carbon is added into a hydroponic nutrient solution it has a direct effect on oxygen levels. The organic carbon is a food source for microbes which naturally live in all hydroponic systems and don't usually cause any harm (beneficial in fact), when large amounts of carbon are available in the nutrient as a food source the microbes feed on this, multiply,(double in population numbers very 20 mins in warm conditions) and as this goes on they use up vast amounts of the dissolved oxygen in the system. At the rate of multiplication of microbes it only takes a few hours in most cases before they have significantly increased the BOD (Biological oxygen demand) of the system to the point where there is not enough oxygen left over for the plant roots. At this point the nutrient goes `anaerobic' meaning no oxygen and often there are bad smells or slime or fur growing in or on the nutrient which further produces toxics which can damage the plant roots and whole thing just goes bad. Very small amounts of organic product can usually be tolerated in a well aerated nutrient solution as the microbes use all the carbon that it provides then when there is no more they die off and stop the loss of any more oxygen. But large amounts or use of a number of different organic additives will de-oxygenate the root zone. Organic compounds include sugars, amino acids, vitamins, enzymes, guano extracts, seaweed and compost extracts etc all of which are great food sources for microbes in solution. Also be wary of those products on the market that are sold for boosting dissolved oxygen in nutrient solutions - most are just bottled hydrogen peroxide or calcium peroxide powder and will oxidise/damage roots (that's a whole other rather long and complex explanation).
Many growers who claim a pathogen has infected the plant roots actually have damage that resulted from a lack of oxygen in the root system and the pathogen infection was secondary to that damage. There has been a huge increase in growers reporting this and I suspect it has a lot to do with the use of many of the `organic' additives on the market these days. When organic additives or organic matter which contains organic carbon is added into a hydroponic nutrient solution it has a direct effect on oxygen levels. The organic carbon is a food source for microbes which naturally live in all hydroponic systems and don't usually cause any harm (beneficial in fact), when large amounts of carbon are available in the nutrient as a food source the microbes feed on this, multiply,(double in population numbers very 20 mins in warm conditions) and as this goes on they use up vast amounts of the dissolved oxygen in the system. At the rate of multiplication of microbes it only takes a few hours in most cases before they have significantly increased the BOD
(Biological oxygen demand) of the system to the point where there is not enough oxygen left over for the plant roots. At this point the nutrient goes `anaerobic' meaning no oxygen and often there are bad smells or slime or fur growing in or on the nutrient which further produces toxics which can damage the plant roots and whole thing just goes bad. Very small amounts of organic product can usually be tolerated in a well aerated nutrient solution as the microbes use all the carbon that it provides then when there is no more they die off and stop the loss of any more oxygen. But large amounts or use of a number of different organic additives will de oxygenate the root zone. So just as a caution- I am aware of the large number of `organic' type additives sold on the hydroponic market as `amazing' plant boosting etc etc nutrient additives, but be very wary of these (organic compounds include sugars, amino acids, vitamins, enzymes, guano extracts, seaweed and compost extracts etc all of which are great food sources for microbes in solution). Also be wary of those products on the market that are sold for boosting dissolved oxygen in nutrient solutions - most are just bottled hydrogen peroxide or calcium peroxide powder and will oxidise/damage roots (that's a whole other rather long and complex explanation). I NEVER use any organic or carbon based compounds in my solution. I’ve seen the solution go anaerobic and it’s quite destructive. I got tired of pontificating DO levels and long ago purchase a meter to know definitively what was happening in my solution.
Root pruning should also be avoided - any time you cut or damage the roots there is a significant increase in the risk of root rot pathogen infection. Many pathogens can't actually attack a healthy and intact root, but if it is cut, then entry is easy and infection can be rapid as roots are in a very damp, moist environment, perfect for infection by fungi and bacteria. Also it serves no physiological purpose unless you are growing `bonsai' trees - root pruning can be used to stunt the plant and restrict the growth and development of the top of the plant which can be used in decorative ornamental trees such as bonsai, but usually we don't want to restrict or delay growth of cropping plants. Also it severely stresses the plant by restricting water and nutrient uptake, so leaving the roots alone is best.
Root systems in plants generally are in proportion to the size of the top of the plant and slightly dependent on species. As the top of the plant increases in size, the root system also grows in proportion, the reason being that it's the surface area of root that is important to be able to take up sufficient water and nutrients in times of high demand to support the size of the top of the plant. A large plant with a small root system, even a very healthy and efficient root system is very uncommon; typically the size of the root system is always in proportion to the top of the plant. If its not, then we would expect there is a problem in the root zone such as lack of oxygen, nutrient imbalance ,high EC, incorrect pH, moisture stress etc and this then restricts growth of the upper portion of the plant. In soil, if water or nutrients are limited you often see very long tap roots developing which grow down in search of water, but in hydroponics this does not occur, although growing hydroponically does not mean that the roots don't need to be large and extensive. There is bit of myth about hydroponics that root systems can remain rather small as they have all the water and nutrients delivered to them, but that's not really the case, large plants in particular need that large surface area of root tissue to be able to absorb sufficient water and nutrients (large volumes) and do that they need an extensive root system. I’ve found that 6 gallon buckets along with the 100% perlite I get fantastic and fuzzy white root development. When the plant is in peak consumption phase (about 4 weeks per run) I’ll go through 3.5 to 4.0 gallons per plant.
When plants go into a rapid reproductive phase and there are flowers/buds/seeds/fruit etc being produced the growth of the root system slows because the plant will direct assimilate into those reproductive parts at the expense of the roots. In some plants, like a heavily fruiting tomato for example this gets so extreme that roots even die back a little at this time as the plant just doesn't give priority to new root growth and regeneration when all its reserves and energy are going into fruit production.
Spray N Grow as a foliar has been extensively and widely tested in both field agriculture and hydroponics
Stay on the veg formula for at least 1 week after switching to 12 hours. By not changing the formulation during this stage, when the plants are going through an adaptation to the new lighting regime, it reduces the level of stress and helps maintain the rate of vegetative growth. After 1 week the plants should be fully adapted to the new lighting conditions and changes to the formulation can then be made. Bloom formulations don't actually speed up the rate of flowering or induce flowering in any way (day length and plant maturity does that), what they do is provide a different ratio of nutrients that the plant requires when going into the reproductive phase. So all that a bloom formulation does is provide the new ratio of nutrients that the plants need once they start flower growth and development, this helps the solution stay in balance longer and prevents depletion of elements such as potassium and phosphorus.
Plants need time to adapt to increases in light and this takes days rather than hours, probably only increase the light once every 7 days, allow the plants to adapt then increase again in another 7 days and always check of signs of high light damage each time (bleaching of foliage, yellowing, drying off of the edges, thickened leaves etc). I do my light increase in 5 to 6 day increments.
Day temp of 75 - 80 is optimal for ambient and low levels of co2 enrichment, once you get past around 450 - 500ppm run the temps a little higher 78 - 84 F. Plants can make far greater use of the additional CO2 if the temps are warmer - both temperature and CO2 are what power photosynthesis so increasing one without the other doesn't give the best increase in photosynthesis possible (watch out for a faster rate of water uptake then this is done). Generally the temps would be run at the lower end of this range during that early veg phase as it helps the plant establish faster and puts less stress on the root system, and at the higher end when going into the flowering phase when you might be boosting the light and CO2 the most. Temps when the lights are off need to be a little cooler 71 - 75F, although warmer night temps won't actually harm the plant, the plants are still respiring at night - respiration is a process that uses up oxygen and release CO2 and it is essential for plant processes, however respiration also uses up plant reserves (assimilate that was produced during the light hours) and the rate of respiration increases dramatically with temperature, so we don't want the plants respiring a whole lot of their stored assimilate during the night. Also a slightly lower night temperature has beneficial physiological effects in flowering plants.
CO2 is toxic and levels of over 2000ppm can be very destructive.
Generally if CO2 is running a bit too high then the plant reacts by initially shutting down photosynthesis (i.e the stomata close in an attempt to protect the plant from toxicity), this prevents the plant from transpiring, even if the humidity levels are fine etc. So the plants may look as if they are starving, losing their green color as chloroplasts are destroyed and no photosynthesis can take place. If the levels are way too high (like over 1600ppm), then a phytotoxicity develops which usually results in rolled, thickened deformed leaves, that may twist and look dark. Young plants are more sensitive to CO2 than older ones. Co2 burners can produce toxic by-products and ethylene if incomplete combustions occurs and this causes significant plant damage (many commercial growers have experienced this). Increasing CO2 will also increase the rate of water uptake and use by the plant as they carry out a higher rate of photosynthesis. Co2 levels of 900 to 1,000ppm, once the plant has adapted to the increases, is best. I’ve seen several Co2 burners produce mystery by-products over the years and have suffered much grief. Now, tho a huge PIA I choose to run bottles instead. (Max of 1,000ppm)
Chloramines are becoming more common in town supply water. It is toxic to plants. Problems usually take around 10 days from damage to symptoms showing up. Plant in dirt are less susceptible to chloramine because of the soils buffering capacity. RO water only for my plant.
UV sterilization of the nutrient solution is not a good idea - it tends to interact with iron chelate in the nutrient solution, making it unavailable for plant uptake and resulting in iron deficiency. UV does have a high kill rate for pathogens, but the problems with iron chelate mean that the grower has to monitor iron levels in solution and adjust accordingly on a regular basis; even then iron deficiency can be a common problem. Some commercial growers do use UV sterilisation for pathogen control in recirculating systems, but when they do so they switch to using different forms of iron chelate such as Fe-EDDHA in their nutrient formulation which are more stable under UV sterilization and they also carry out regular iron chelate testing. That's probably not practical when using a nutrient premix such as GH or any of the others
Large lava chunks is sort of like a vertical NFT with nutrient cascading down the rock particles 24/7, which is O.K, but the plant will put energy into growing roots directly downwards, following the flow of nutrient rather then producing a highly branched root system that fills out the whole bucket with roots. Also there are likely to be pores inside the rock that pathogens, and old root material might accumulate in, creating a disease risk and it can be hard to disinfect media with that sort of porous structure. Lava is way left over from the 'old days'. I haven't touched the stuff in years.
Fluffy white root hairs which will maximize the surface area of the root and hence nutrient and water uptake. We never get these types of roots in lava. Perlite has great root development.
Keeping the EC stable is important - letting the nutrient dilute creates a situation of continually changing osmotic potential in the root zone and can create a bit of osmotic shock if allowed to dilute to much and then the EC is suddenly increased. Plants need a little time to adjust to changes in EC, so just adjusting the EC back each day gives a small change in EC rather than a large one. You would notice that as the EC diluted the plants took up more water, which is just an effect of the lower of the osmotic potential in the root zone.
H2O2 will oxidize completely if there is sufficient `organic' matter in the system for it to work on, oxidize and then deactivate. If you have a clean system, it has nothing to work on and hence won't deactivate and can attack roots instead if there is a build up.
As a last resort `Captan WG' (note it has to be the WG formulation) can be used for root rot and damping off (Pythium) pathogens, but don't use it `just in case' and if you can always trail these things in one system at a dilute rate first to see if there is any adverse reaction.
H2O2 is a powerful oxidant, it will oxidize organic matter in the system/nutrient, however the rate needed to kill fungal spores on average is at least 100 - 120ppm, more for persistent spores, up to200ppm and a contact time of 20 mins. However, we know that rates ofH2O2 as low as 6ppm will damage seedling roots, particularly in clean systems where the active H2O2 has no other organic matter to work on. I think your more mature plants would not have been badly affected by this, but the rate was high enough to have a negative effect on young plants in a clean system. H2O2 works by oxidizing all organic matter, including live root systems- live roots are a little more resistant to oxidation than dead root material, or spores, but can still be damaged. H2O2 damaged roots tend to brown off and go mushy, so the damage looks a lot like the pathogen growers are trying to kill off with the H2O2 in the first place. What we have seen with cucumber crops is that while the plant doesn't die off, they still look healthy; they ended up being about 20% shorter and about 2 weeks delayed when H2O2 was used in the nutrient at low rates.
Since you would have to add 10 times the dose you used to actually kill off any pathogen spores and since that would certainly burn back a lot of roots, its best to just not use it. H2O2 is fine to use for cleaning up your equipment and system between crops (use at least 300ppm to do so), but rinse really well with water to remove residues before replanting.
RO flush, if necessary, just long enough to get a few good rinses through, no more than 2 hours even if you have to manually rinse the media. Plain water won't kill the plants - when plants which have been in nutrient solution of a given strength then receive just water or lower strength solution the osmotic potential actually drops so that the plants can take up more water, faster. If the EC is increased in strength rapidly and high EC levels are then run, then the osmotic potential increases and the plant root cells actually loose water back into the nutrient solution and dehydrate somewhat. I flush my media thoroughly every 7 days.
High EC. Using really ‘aggressive’ strength EC levels doesn't give faster growth and more nutrient uptake but can actually stress plants as they struggle to take up water. On the other hand using high EC promotes shorter, more compact growth, increased flavour in fruit etc. So giving the plants a couple of hours of plain water is not really long enough to cause any major effects on plant growth, but the lower EC after that allows them to take up water and nutrients easier in their current state of health and might get them back feeding again. This is a standard commercial practice for plants that seem to have stopped growing or taking up nutrients in are circulating system - kinda like a `detox' for plants that will kick start them back into growth by getting rid of any build up, but it has to be good quality water and no `flushing products'.
Potassium levels are kept up with the use of the potassium hydroxide and potassium silicate and even accumulates a little and can end up accumulating with insufficient nitrogen in the ratio of elements(and possibility insufficient calcium as well).
In GH nutes there is around 4 - 5% NH4 form of nitrogen - this is what gives it `pH buffering capacity' that is it keep the pH down when the plants are taking up ions from solution. However the faster the plants are growing and taking out nutrients, the faster the pH comes down and it seems to run on the low side.
In the end of all that I have a system, protocol, and knowledge base that works for me. I can consistently pull down round after healthy round and that’s good enough for me.
Peace
Below is what my lower bkts look like. However, the plumbing has changed some. I no longer have 2" of DWC and air. The drain is directly on the bottom of these containers and the air has been removed. My reservoirs are heavily aerated tho.
