DWC, RDWC and RECIRCULATING SYSYEM TOP UP EXPLAINED.

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Aqua Man

Aqua Man

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Ok I'm going to explain a more complex way of maintaining our systems for those looking to use best practices (IMO only) There are many ways this can be done but I feel this gives the most stability for PH, PPM, NUTRIENT RATIOS (super important) especially is systems with a low water volume.

So we all do our res changes at various times and I won't get into that here. But what about between them? How can we best keep our PH, ppm and nutrient ratios as close to our goals as possible?

How i do it is by steering them with my top ups. This is nothing new but I see many asking these questions or missing the benefits of this method.

How do we do this?

Well as complicated as it may sound, its actually quite easy but first let's make sure we are getting accurate info to use in how we calculate this. Garbage info in equals garbage info out.

We want the total volume of water in the system (Not the volume the system holds) This is important as the closer we get the better the calculations work. Now it's not the end of the world being a bit off.

Things to consider.

Amount of water in each site (this will change as the roots grow and displace water)

Amount of water in the res (if you have)

Ok thats about that lol.

Now let's get into the calculations step by step.

1. Take the PPM reading after filling the system up. Write this down.

2. The first top off will be done with just water. After filling take the PPM reading. Then take your original res PPM from step 1 and minus the reading from step 2. This will give you a ppm difference that will show how many ppm of nutrients the plants have consumed.

3. Now for every top up following.... We take the volume of water of the system filled and divide it by the amount of water we need to add back to reach filled. Then we multiply it by the difference found in step 2.

4. Add the desired ppm of the system.

this will give you exactly how much ppm you need to add of your nutrients to the volume added back to get the system back to its original PPM.

EG 1 first calculation after only water top up.

We have a system that holds 20gal of water, we want 600ppm for this stage of growth. It has 4 sites and the 4 plants are drinking 3.5 gal a day. The PPM difference from last top up with just water was 90ppm which means the system was at 510ppm and we want to bring this back up close to 600ppm using our 3.5gal top up.

So we take our 20gal(total water volume) divided by 3.5 (top up) gives us 5.7

We take that 5.7 x 90 (90ppm difference) gives us 513+600(target ppm) =1113ppm

So we if we take our 3.5 gal of top up water and add 1113ppm of balanced nutrients to it. Then top our system up we should be close to our 600ppm starting point and we have added back balanced nutrients to help combat any ratio changes in the system.

TLDR:

(Total volume of water) divided by (top up volume) multiplied by (ppm difference after last top up) plus (target ppm)
 
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N4M

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to add on for clarification
Step 2 if not using RO water, you want to add your water's ppm to that calculated ppm

Original res 500
Add water ~100
new ppm 545

545 - 500 = 45 + 100 = 145 ppm consumed (or maybe it's 55? 500 (original) - 545 (new) = -45 + 100 = 55)

1. Take the PPM reading after filling the system up. Write this down.

2. The first top off will be done with just water. After filling take the PPM reading. Then take your original res PPM from step 1 and minus the reading from step 2. This will give you a ppm difference that will show how many ppm of nutrients the plants have consumed.
 
Last edited:
tsukiman13

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to add on for clarification
Step 2 if not using RO water, you want to add your water's ppm to that calculated ppm

Original res 500
Add water ~100
new ppm 545

545 - 500 = 45 + 100 = 145 ppm consumed
Good catch! 😁

And yay, @Aqua Man thank you sir. Love some good info.
 
Aqua Man

Aqua Man

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to add on for clarification
Step 2 if not using RO water, you want to add your water's ppm to that calculated ppm

Original res 500
Add water ~100
new ppm 545

545 - 500 = 45 + 100 = 145 ppm consumed (or maybe it's 55? 500 (original) - 545 (new) = -45 + 100 = 55)
I dont bother because the ppm of the source water is already part of the starting make up but yes you can take into account the ppm of source water. Usually I take this into account with the starting ppm.

As we just want to be close I dont find it critical.
 
Aqua Man

Aqua Man

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I should probably add that I only top up with water until I'm about 20% lower than my target. So if I'm at 600ppm target I dont do nutrient tops ups until I'm about 480ppm. Usually every second day in my system.
 
tsukiman13

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I should probably add that I only top up with water until I'm about 20% lower than my target. So if I'm at 600ppm target I dont do nutrient tops ups until I'm about 480ppm. Usually every second day in my system.
Wait, so even if the water is down to half and still not getting close to 20%? Im just wondering
 
tobh

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awesome, thanks for this! highlighted a mistake on my part in the process of fumbling through the first stumbling blocks of getting into full hydro.
 
CF89

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I dont bother because the ppm of the source water is already part of the starting make up but yes you can take into account the ppm of source water. Usually I take this into account with the starting ppm.

As we just want to be close I dont find it critical.

My tap water is 110ppm

why would I add 110ppm to the equation just to remove 110ppm later on?

is that what you’re saying?
 
tobh

tobh

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My tap water is 110ppm

why would I add 110ppm to the equation just to remove 110ppm later on?

is that what you’re saying?

Because it's irrelevant at the end. You don't know what that 110ppm consists of, but it will result in your final solution being 110ppm higher if you don't remove it.

You always factor in your initial ppm. Often you can safely assume it's some concentration of calcium, chlorine, cloramine, fluoride, minerals, etc.

But, it's important to factor it in initially so you know your true number of nutrients added to the solution. The adding/removing ensures you know you added, for instance, 500 PPM nutrients to your solution as if your water started with 0 ppm water.
 
dusty68

dusty68

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Well my system is 4 site with 25gal res. Its never gets that low. In a smaller system you may need to every top up

As usually I would do daily top ups.
I have to do daily top offs depending on how big the girls are. I am only using 4- 5 gallon buckets in a fallponic recirculating system with 2" returns and a 5 gallon res. If they are vegging strong, I need to add RO water daily (2=3 gallons). This works for my grows but I am interested in Aquamans method and may try it.
 
dusty68

dusty68

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Hi Aquaman, If I build a larger res (not a concern, I have some skills) for my next grow, is it possible will I need to do less top offs and water changes? I currently mix and change 25 gallons (the whole shebang) at one time once a week or so.
 
Aqua Man

Aqua Man

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Hi Aquaman, If I build a larger res (not a concern, I have some skills) for my next grow, is it possible will I need to do less top offs and water changes? I currently mix and change 25 gallons (the whole shebang) at one time once a week or so.
Absolutely will reduce the need for frequency of top off and res changes. Also will provide a more stable ph and ppm. But will use more nutrients.

Do a water change based on add backs. Once you have added back the volume of water equal to the ACTUAL water volume of the system. Then do a water change. In early stages you may go 3 weeks or more without a changeout and mid flower maybe once a week. This helps cut back on unnecessary water changes. The reason is the less they take up the less change in nutrients ratios. So you can just steer the res with top ups to get your ppm and ph and your adding back proper ratios so each top up help bring the ratios back towards balanced and if you change the res after your add back equal the volume then you should never have an issue with ratios going to far out as to create an issue and like I said in the earlier stages you save a lot of wasted water changes.
 
TheBioMaster

TheBioMaster

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Wow! I been running RDWC for 10 plus years now......and NEVER do any of that! In fact it kinda confused me! LOL!

1. Change your tank every seven days.....

2. Don't use cal/mag

3. Use RO water

Done.

There is no "top up" needed or used in RDWC. You have a epicenter, and a res tank, with a proper system. Your not "topping off" anything.

Until I adopted this method, after YEARS of system design changes trying to fight the problems.....everything fell into place.

It amazes me to see people reinvented the wheel over and over with these attempts at detailed instructions and explaining..... When nothing could be easier really......

Good luck with your topping off and what not.......
 
Aqua Man

Aqua Man

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Wow! I been running RDWC for 10 plus years now......and NEVER do any of that! In fact it kinda confused me! LOL!

1. Change your tank every seven days.....

2. Don't use cal/mag

3. Use RO water

Done.

There is no "top up" needed or used in RDWC. You have a epicenter, and a res tank, with a proper system. Your not "topping off" anything.

Until I adopted this method, after YEARS of system design changes trying to fight the problems.....everything fell into place.

It amazes me to see people reinvented the wheel over and over with these attempts at detailed instructions and explaining..... When nothing could be easier really......

Good luck with your topping off and what not.......
So 7 days later you throw your perfectly good nutrients out? How much do tiny seedling eat that you need to change it after 7 days?

You plants don't drink so you don't need top ups? Hell 4 plants in mid flower in my system drink over 5 gal a day. How is this possible you dont need to top up? And just change once a week?

This has been around forever just not widely used in hydro. Part of it is based off EI dosing and calculating at what point nutrient ratios become unbalanced through a massive amount of testing over many years... granted not in the hydroponic Industry. Changing water weekly is an outdated and poor practice that actually came from the same place..... the aquarium hobby.

Over 20 years I spent breeding fish and propagating aquatic plants and mixing my own nutrients before even stepping into hydro.

Weekly water changes are about as ancient as it gets, very wasteful in early stages and possibly not enough in the latter stages depending on the volume of water you work with.

RO and no cal mag? For some nutrients yes but others no and I would never make such a blanket statement on that just the same as weekly water changes.
 
airedog

airedog

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Before, i ran a half-strength top-up res controlled by a float valve. Usually did a complete system change-out every 7 days though as even if i knew the solution strength after top-ups i wasn't sure if my nutrient ratios had stayed constant. I was running a 4 site UCXXL13 rig and by mid-flower they were drinking 30 -50 L day; that's also about the time i started getting wicked pH drops and i eventually started changing out more frequently.

I also used Bud Factor X to increase resin production and boost terpenes, at the expense of making the plants think they were under attack. Makes it kinda hard to differentiate between nute deficiencies and side-effects of supplements, but inherent in any grow method is the development of 'listening to your plants'.

As usual, Aquaman has given me effective guidelines for improvement and lots more to think about.
 
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