PH A Basic explanation

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IrishRob

IrishRob

OK I'm going to do my best to explain PH since its something that is for the most part greatly misunderstood and can be confusing to new growers and even experienced growers alike. This will explain why we need both ppm and PH meters to give us informed information about PH

This will be a simple guide leaving out a lot of information. So lets get started with a couple of definitions to help you understand.

What is PH?

PH is a measurement of how alkaline or acid a solution is based on measuring hydrogen ions. It tells us nothing more than the ratio of acidic to alkaline elements. It does not tell us how much of each the solution contains or the alkalinity of the water.

What is alkalinity?

Alkalinity is the measurement of the waters buffering capacity (ability to neutralize acids). Its the total amount of carbonate and bicarbonate in the water that affects its ability to resist change to PH. If you know the alkalinity you can actually calculate the amount of acid of varying types needed to reach your target PH but we wont get into that.


So now we have a basic understanding of the difference lets get into some examples of source water and how alkalinity will affect PH.

RO and Distilled water

Ro and Distilled water is very low in mineral content containing carbonate or bicarbonate sources, we know this because if we test the ppm its usually under 40 and as low as 0ppm. This means it has a very low alkalinity (ability to neutralize acids) and is easily influenced by anything added that's acidic. But likewise it does not contain acid and is easily influenced by anything added that's basic. This results in a very unstable PH that can be easily influenced by anything added or anything its added to. In hydro the ideal ppm of carbonate/bicarbonate sources to provide an adequate buffer will be 50-100ppm with 75ppm being the target. Less than this and PH may swing to fast and be unstable, more and it will not drift enough and will require too much acid that could affect nutrient ratio's negatively depending on the acid used. By adding alkalinity and then acid we provide a more stable PH because adding more of either will have less impact on the overall ratio of acidic to basic elements

When used in hydro it should have alkalinity (a buffer) added back to prevent wild PH swings. Any source of carbonates, bicarbonates, silicates or hydroxides will work to create alkalinity. Sources i would recommend would be calcium carbonate, potassium bicarbonate (commonly sold as PH up) and finally what i would consider the best option is potassium silicate as it is a source of potassium and silica which are both excellent for cannabis. When using RO or distilled you will want to add back some calcium and magnesium if your nutrients are not designed for RO/distilled water as that's usually what Ro filters are removing for the majority. But most cal/mag is in the form of nitrate and provides no alkalinity (buffering capacity) so adding one of the previously mentioned or other is still a must.

When used in soil this unstable PH is actually IMO beneficial if you have a pre buffered soil (which you should) This means the water will have no impact on the PH potential (more on this later) of the soil and will almost instantly be influenced by the soil to the take on the PH of the soil makeup. This is why i feel we do not need to be PHing our nutrient solution for soil grows (unlike soiless and hydro). The soil is what will adjust the PH of our nutrient solution.

Tap Water

OK we all know tap water varies a lot form place to place and I will explain the basics of how to determine if your tap water is suitable or not for use. First we want the PPM and second we want the makeup of that ppm if available. Generally speaking the majority of the PPM makeup will be calcium carbonate. This is used to buffer the water supply and prevent acidic conditions that erode the coatings and will break down piping and leach them into the water supply such a lead (Flint Michigan ring a bell?) So we can generally assume the majority of the PPM in tap water is likely calcium carbonate but also some others like magnesium, sulfur, phospahte, iron etc. So if you have a ppm of 100-200ppm you can assume roughly 50-75% of that is calcium carbonate. Remember our target is 75ppm carbonate/bicarbonate sources to provide an ideal alkalinity (hope we are starting to see how import alkalinity is and we can't just go by PH) Now there are some cases when some sodium may be used such as sodium bicarbonate aka baking soda (can also be used as a buffer in a pinch but not recommended as a long term option) so we can google our local water report and see the makeup of the ppm in the water.

Soil PH potential

Now when we buy a prebufferd soil like most of the ones we use they come "Prebuffered" (alkalinity adjusted) what does this mean? This means the company has added amendments that when water is added the resulting PH of the water in the soil will be in a favorable range for growing our plants. Often times peat is used to lower PH and lime is used to raise PH in these soils. Just like in water we want to control the alkalinity (buffering capacity) of the soil to have a stable PH that is not easily influenced by adding things such as nutrients or other. Unlike hydro and soiless where we control the alkalinity (buffering capacity) of the water by adding it directly to the water it is applied to the soil. Which brings me back to my point of we don't need to PH our nutrient solution in soil because the soil provides the buffering and will adjust the PH. Now things like lime and peat break down slowly over time and only soluble elements will impact PH so this is how they control the PH in soil over long periods of time, because it breaks down slowly and only a small amount is soluble at a time its unlikely after a grow it has been depleted. But if we are reusing the soil we should be looking at re amending the buffering capacity before using again to ensure there is enough to last through the next grow. Often times farmers will do this once a year before seeding crops.

Effects of nutrients and source water on PH

First the PH down acids we use tend to break down much faster than the alkaline sources we use in both hydro and soil. For this reason we see a hydro systems PH generally rise over time unless something is creating more acid like decaying roots in which case we may actually see PH going down. Typically a PH increase of 0.2 in a 24 hr period is desirable and by adjusting the alkalinity we can control the PH drift. In the case of soil the acids used to bring PH down before feeding break down quickly and the alkaline and acidic buffer we have created minimizes the impact so they are really of not much benefit and have virtually no impact on long term PH potential of the soil. This is why we can't use them to lower high soil PH once we have an alkaline source buildup. However in hydro and coco PHing the nutrient solution is important because unlike soil there is not an adequate buffer established although in coco it is possible to do so.

Generally speaking the ratio's of nutrients we use will be acidic so when we get a buildup of nutrients we will almost always see PH drop. This is where you often hear ppl say flush the media. What this does is dilutes the dissolved elements and will remove some from the media in runoff.

Conversely a water source with high alkalinity can build up in the media and cause the PH potential of the soil to rise over time and in turn the PH of the water added to it. This is the reason we should look at the alkalinity of the water source not the PH as PH cannot measure the potential influence but rather only result.

Often in both circumstances its a good idea to flush the media to remove excess amount of available elements that may be affecting the PH negatively.

I'm gonna stop there and if anyone has questions i will do my best to answer them. If you have something you would like to add please do.


Aqua Man
Wow thank you so much. That's exactly what I needed to know
 
KingHale

KingHale

I had to read through this thread twice ... I’m quite certain that the majority of my mistakes can be fixed right here so I wanted to confirm something and ask a couple of questions.

1) I have a soil grow, Fox Farm Happy Frog and I’m using rainwater that runs off of my gutter system and then gets filtered and stored in 5 gallon buckets before it’s filtered a second time and prepped with general hydroponics pH up/ down. You’re saying I probably don’t have to pay balance my nutrients because the soil acts as a buffer? I had a gut feeling about that. So then, what value would there be in pH balancing the non-nutrient water? Wouldn’t the soil buffer non-nutrient water similarly?

2) I see that testing kits for alkalinity of water are quite involved. There doesn’t seem to be a simple meter like my blue labs pH meter. Any suggestions or recommendations? Also, the recommended alkalinity of water for growing in soil would be below 40ppm correct?

3) no matter what happens, if my soil pH meter is reading good, I should be good on alkalinity and pH right?

Thanks again for everyone’s assistance! I had no idea how complex this was going to get. It’s easy to get overwhelmed with it all but I’m taking it one piece of the puzzle at a time. Next I’m going to learn about pest management and then I’d love to learn more about “re-amending the buffering capacity of re-used soil”.
 
Aqua Man

Aqua Man

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I had to read through this thread twice ... I’m quite certain that the majority of my mistakes can be fixed right here so I wanted to confirm something and ask a couple of questions.

1) I have a soil grow, Fox Farm Happy Frog and I’m using rainwater that runs off of my gutter system and then gets filtered and stored in 5 gallon buckets before it’s filtered a second time and prepped with general hydroponics pH up/ down. You’re saying I probably don’t have to pay balance my nutrients because the soil acts as a buffer? I had a gut feeling about that. So then, what value would there be in pH balancing the non-nutrient water? Wouldn’t the soil buffer non-nutrient water similarly?

2) I see that testing kits for alkalinity of water are quite involved. There doesn’t seem to be a simple meter like my blue labs pH meter. Any suggestions or recommendations? Also, the recommended alkalinity of water for growing in soil would be below 40ppm correct?

3) no matter what happens, if my soil pH meter is reading good, I should be good on alkalinity and pH right?

Thanks again for everyone’s assistance! I had no idea how complex this was going to get. It’s easy to get overwhelmed with it all but I’m taking it one piece of the puzzle at a time. Next I’m going to learn about pest management and then I’d love to learn more about “re-amending the buffering capacity of re-used soil”.
As long as the ph stays reasonable during mixing nutes imo no need to ph adjust at all. Ph issues during mixing are usually involved when you are using silica other than that mix as directed by the manufacturer and just feed.
 
KingHale

KingHale

As long as the ph stays reasonable during mixing nutes imo no need to ph adjust at all. Ph issues during mixing are usually involved when you are using silica other than that mix as directed by the manufacturer and just feed.
Following manufacturer instructions is one of my favorite things to do in life. Sometimes the manufacturers instructions aren’t completely clear and I’m a tad OCD. For instance, Fox Farms instructions are thus:

“FOR BEST RESULTS: feed two times per week. Maintain a pH of 5.6 to 6.8 to prevent nutrient lockout and reduce stress on plants”

For me, this meant to pH the water prior to feeding, I never thought to check the pH of the water prior to adding nutrients. You’re saying that if the pH doesn’t change drastically after adding nutrients, that means the alkalinity of my water should be compatible with the buffering quality of my soil medium? I’m probably over-thinking everything. So long as my soil pH meter reading is good, I’ve got nothing to worry about where the alkalinity of my water is concerned, Right? Thanks in advance.
 
Aqua Man

Aqua Man

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Following manufacturer instructions is one of my favorite things to do in life. Sometimes the manufacturers instructions aren’t completely clear and I’m a tad OCD. For instance, Fox Farms instructions are thus:

“FOR BEST RESULTS: feed two times per week. Maintain a pH of 5.6 to 6.8 to prevent nutrient lockout and reduce stress on plants”

For me, this meant to pH the water prior to feeding, I never thought to check the pH of the water prior to adding nutrients. You’re saying that if the pH doesn’t change drastically after adding nutrients, that means the alkalinity of my water should be compatible with the buffering quality of my soil medium? I’m probably over-thinking everything. So long as my soil pH meter reading is good, I’ve got nothing to worry about where the alkalinity of my water is concerned, Right? Thanks in advance.
Your nutrients should be fine if thats all your using. Rainwater is like RO water its very low alkalinity and if filtered should be fine.
 
Glassdub

Glassdub

Following manufacturer instructions is one of my favorite things to do in life. Sometimes the manufacturers instructions aren’t completely clear and I’m a tad OCD. For instance, Fox Farms instructions are thus:

“FOR BEST RESULTS: feed two times per week. Maintain a pH of 5.6 to 6.8 to prevent nutrient lockout and reduce stress on plants”

For me, this meant to pH the water prior to feeding, I never thought to check the pH of the water prior to adding nutrients. You’re saying that if the pH doesn’t change drastically after adding nutrients, that means the alkalinity of my water should be compatible with the buffering quality of my soil medium? I’m probably over-thinking everything. So long as my soil pH meter reading is good, I’ve got nothing to worry about where the alkalinity of my water is concerned, Right? Thanks in advance.
At this point I don't worry too much about the pH of the water as much as the runoff pH, as of my last watering in going pH was 10.7 (tap water & amendments) & the run offs were between 5.7-6.2, this is what to watch, I made the mistake of aciding down my in going solution pH prior & it probably did more damage than good.
 
XtreemLee

XtreemLee

Thanks for everyone’s input:

my list
Verify well water ec. That’s important I need to really understand what my starting point is. I ordered some cal/mag and another drop style ph test system. I use a Hanna pen that does ph and ec, I recalibrate often, but have had issues with it in the past. I have strips I use when I have doubts but paper and color is only so good.
I need to pay attention to ec better. I think I have been adding to much nutrients. I usually pull water and let it warm up as well water is cold.
I will check ph and ec of my well water and verify what I’ve said previously.
I haven’t cleaned my buckets or net pots very well and went through everything today. I can’t clean the net pots that have plants in them but I can clean everything else, and am doing that with hydrogen peroxide and water.
So my plan is as follows:
Verify well water ph and ec, I’m confident my ph is 8 but never really looked at incoming ec.
Once I have that I have to flush these plants with the net pots and gravel that’s already in place. I don’t think the stress of flushing is any worse than my ph being out of control.
Then i am going to let them sit in ph balanced well water. Let that go for day and check again. Again, I’m listening and I’ve read all you’ve posted.

I don’t balance ph until I’ve added all nutes, cause my nutes always change it a bit.
 
Aqua Man

Aqua Man

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Thanks for everyone’s input:

my list
Verify well water ec. That’s important I need to really understand what my starting point is. I ordered some cal/mag and another drop style ph test system. I use a Hanna pen that does ph and ec, I recalibrate often, but have had issues with it in the past. I have strips I use when I have doubts but paper and color is only so good.
I need to pay attention to ec better. I think I have been adding to much nutrients. I usually pull water and let it warm up as well water is cold.
I will check ph and ec of my well water and verify what I’ve said previously.
I haven’t cleaned my buckets or net pots very well and went through everything today. I can’t clean the net pots that have plants in them but I can clean everything else, and am doing that with hydrogen peroxide and water.
So my plan is as follows:
Verify well water ph and ec, I’m confident my ph is 8 but never really looked at incoming ec.
Once I have that I have to flush these plants with the net pots and gravel that’s already in place. I don’t think the stress of flushing is any worse than my ph being out of control.
Then i am going to let them sit in ph balanced well water. Let that go for day and check again. Again, I’m listening and I’ve read all you’ve posted.

I don’t balance ph until I’ve added all nutes, cause my nutes always change it a bit.
Imo you always want nutrients in hydro. If flushing flush with the nutrients in ph and teml adjusted water. I top feed from the res once a week just to clear any salt buildup.
 
Pondracer

Pondracer

Imo you always want nutrients in hydro. If flushing flush with the nutrients in ph and teml adjusted water. I top feed from the res once a week just to clear any salt buildup.

Thats interesting. I haven't flushed this time at all other than when I moved them into flower, though one plant could have used it. Really fun run this time with two plants in 2 gallon fabric and I had two in plastic containers less than one gallon. I did transplant those into 2 gallon fabric. All four were roughly 3' tall and about 30 inches wide. Its been really cool to see the difference between these plants and the first two. So much comes down to experience making things easier.
 
Madmax

Madmax

Yeah silica will. You need to mix it in order. Silica first then ph down to 6.2-6.4 ish then add the rest. If you add silica first check the ph after it will be pretty high and can cause things like iron and calcium to precipitate out of the nutrient solution.
Great thread...this is interesting as i havnt been phing after using si first.so does can cause mean it may or may not precipitate out.if it was i would b seeing deficiencies right.been using it for 30 days in flower so far.im not using ph up down most times as when i mix its pretty much bang on but over a day it can climb .1 etc..i dont want to use all that ph down to get it right then mix a+b in then have to ph up quite abit to get it to 5.9-6.0 etc..my tank water is 6.1 -6.3... i was told to use the silica last as itz an additive but ive read it can precipitate out..
 
Aqua Man

Aqua Man

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Great thread...this is interesting as i havnt been phing after using si first.so does can cause mean it may or may not precipitate out.if it was i would b seeing deficiencies right.been using it for 30 days in flower so far.im not using ph up down most times as when i mix its pretty much bang on but over a day it can climb .1 etc..i dont want to use all that ph down to get it right then mix a+b in then have to ph up quite abit to get it to 5.9-6.0 etc..my tank water is 6.1 -6.3... i was told to use the silica last as itz an additive but ive read it can precipitate out..
You will see if it is... will be white particles like a snow globe or settled on the bottom.
 
Madmax

Madmax

Is that for silicon your answer...What about the cal and iron bro..spose there is some form of test or even a meter to test if cal and iron is gone?..
 
Aqua Man

Aqua Man

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Is that for silicon your answer...What about the cal and iron bro..spose there is some form of test or even a meter to test if cal and iron is gone?..
Iron will look like rust. If its flowable silicone no issue but if its something like potassium silicate I would mix properly. I think both should be given time though and added first but I could be wrong on the flowable stuff.
 
Madmax

Madmax

But i dont want to use all that ph down 😭..dont ask me why 😃.. maybe i should ask haha..can using too much ph down have an effect on media ph.im one of those guys when things are looking good im reluctant to change lol..
 
Aqua Man

Aqua Man

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But i dont want to use all that ph down 😭..dont ask me why 😃.. maybe i should ask haha..can using too much ph down have an effect on media ph.im one of those guys when things are looking good im reluctant to change lol..
What media are you in? There are other options like rice hulls and vermiculite also can foliar spray it which is more effective.
 
Madmax

Madmax

Coco coir.when i dont use the silica i have to ph up quite abit and the way i think is that using too much over a period can raise the media ph but im only just guessing that..
 
Madmax

Madmax

Ok i mixed it up how you said to.Aqua 3ml si to 16 litres = 9.2 ph .used 1ml of ph down to 5.8....gave that a good rest then added flores a&b 30ml ea ,20ml boost and 3ml go roots =600ppm im feeding them.its ph then was 4.9 ..added 3/4 ml to get it to 5.9 ..checked ppm and was 6-700 ppm so had to reduce feed by a litre to bring it back..its actually reduced the feed i was giving it not by much and added say 50ppm of up &down to total..so when i reduced it to 600ppm .there wouldnt b 600ppm of feed it there now would there..im still not keen to do it like this lol..
 
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