Grow Mediums DIY Auto feeding system to control ppm and ph

[tetrasect]

Hey guys,

So this has probably been done but I couldn't find anything.

I thought of a simple way to automate feeding to keep steady ppm and ph values with use of a fertilizer feeding tank above the reservoir connected to a float valve.

I guess it can be used in any hydro system but I will use a RDWC here as an example.

Please excuse the crude drawing.

So we see here FT is the fertilizer tank, R is the reservoir and B1-4 are the buckets.
The fertilizer tank feeds into the reservoir when the water level drops.

Basically we are going to measure how much water and fertilizer the plants use to calculate how strong to make our nutes in the fertilizer tank.

It would be best to dilute your ph down so that 1 drop of ph down drops the ph of 1 liter of res water by 1 ph.

SETUP

First we need to know how much water is in the RDWC system (reservoir + buckets).

Starting with an empty system, measure how much water you use to fill up the res and buckets making sure to fill the last bit from the fertilizer tank so as not to submerse the ball valve beyond the shut-off level. In this example the res + buckets hold 100 liters.

Next, add your nutrients to your desired ppm and adjust ph taking note of the ph before adjustment and how much ph down you are using to get to your target ph. In this example we will make a 300ppm solution and add 100 drops of ph down to adjust from 6.8 to 5.8 ph.

Now fill up your fertilizer tank with water, taking note of how much you put in and then measure the ppm. In this example I will be using water that reads 60ppm filled up to 40 liters.

MEASUREMENT

Now that we know all the different numbers going in, we wait. Say we leave the system for 4 days (could be any number of days, as long as there is a significant change in ppm) and come back to see that 10 liters have been depleted from the fertilizer tank. We then check the ppm and ph in the reservoir. Lets say the ppm is at 250ppm and the ph is at 6. Take a note of that and adjust the ppm and res back to 300ppm and 5.8 ph.

ADJUSTMENT

So we saw that the ppm has dropped by 50ppm and the ph has risen by 0.2.

PPM

To calculate how many ppm we should increase our solution in the fertilizer tank by, we take the rise in ppm (50ppm) times the volume of water in the system (100L) divided by the volume of water depleted from the fertilizer tank (10L).

So 50 x 100 / 10 = 500ppm is how many ppm we have to increase the solution in the fertilizer tank by.

Our fertilizer tank currently has 60ppm water in it so we add nutes till we are up to 560ppm, then ph to 5.8.

PH

To calculate how many drops of ph down per liter we should increase our solution in the fertilizer tank by, we take the rise in ph (0.2 ph) times the amount of ph down needed to drop the res ph by 1 ph (100 drops) divided by the volume of water depleted from the fertilizer tank (10L).

So 0.2 x 100 / 10 = 2 drops of ph down per liter is how much we have to increase the solution in the fertilizer tank by.

Our fertilizer tank currently has 0 drops of ph down in it, so 0 + 2 = 2 drops per liter

Our tank holds 40 liters so we will need 2 x 40 = 80 drops of ph down.

RE-ADJUSTMENT

Now if the plants keep feeding at the same ratio of water to nutes, all you have to do is refill the fertilizer tank with a nutrient solution at 560ppm and 2 drops of ph down per liter and your res should stay at 300ppm and 5.8ph indefinitely.

Your plants may start changing their feeding habits though, so lets say you go check on them a week later. There are 12 liters gone from the fertilizer tank,the res is at 280ppm and your ph is at 5.9.
Write those numbers down and then adjust the ppm and ph in the res back to 300ppm and 5.8ph

Now we do the same calculation again:

PPM

Drop in ppm (20ppm) times the volume of water in the system (100L) divided by the volume of water depleted from the fertilizer tank (12L).

So 20 x 100 / 12 = 167ppm

That is how many ppm we have to increase the solution in the fertilizer tank by.

So 560ppm + 167ppm = 727ppm is our target ppm.

PH

Rise in ph (0.1 ph) times the amount of ph down needed to drop the res ph by 1 ph (100 drops) divided by the volume of water depleted from the fertilizer tank (12L).

So 0.1 x 100 / 12 = 0.83 drops of ph down per liter is how much we should increase it by.

So 2 drops + 0.83 = 2.83 drops per liter, so for a 40 liter tank we would need 113 drops.

However, our fertilizer tank still has 28 liters of solution which contains 2 drops of ph down per liter.
28 x 2 drops = 56 drops

So the total amount of drops needed to get to 113 drops would be 113 - 56 = 57 drops.

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Dunno if I explained this in a way that normal people can understand... but yeah, this should keep ppm and ph really steady and drastically reduce the amount of times you need to check on things.

I wrote this in kind of a rush so let me know if I made any mistakes or if the whole thing even makes sense lol

 

[Muddy]

lol, seems you've over complicated things a bit. What you are describing is called a top off res and is what Current Culture recommends for all their rdwc systems. I run a CC UC8XL system which holds 50 gallons of solution. Eight plant pots plus what CC calls the Epicenter, which you are calling your res. It's an 8 gallon bucket, same size as the plant buckets. It's primary purpose isn't as a res but a place to add nutrients, supply additional aeration and monitor the system. My top off res is 30 gallons and connects to the epi via a float valve. Simply mix your top off to the same ppm as your system, adjust the pH to around 5.8 and you're good to go. Monitor your system daily and as long as you are getting a slight drop in ppm while the pH slowly rises you're golden.

 

[EvilScotsman]

hey bud ive seen quite a few guys on here with recirculating systems and to be honest, i dont quite buy it. i tried 2 plants in a 20L recirculating nft res last time and the one closest to the pump was twice the size and always much healthier. it caused the further plant to have deficiencies and had to put an airstone in eventually as the first one started stealing all the oxygen aswell. im asking this as you sound like you know this pretty well and im always looking to learn. but how do you deal with this happening in this system? are the first 2 plants not gonna be much bigger? also ive just noticed, your return pipe should be at the opposite end of the tank to ensure more time for mixing into the feed comming down and the contents of the res before getting pumped back onto the plants. again mate im not trying to be cheeky or that i just generally dont understand why these systems would be of any benefit other than cutting down man hours. sorry if that sounds a bit abrupt mate, just read it back. i dont mean it that way its just me lol. im quite direct when im curious i cant help it lol

 

[Muddy]

hey bud ive seen quite a few guys on here with recirculating systems and to be honest, i dont quite buy it. i tried 2 plants in a 20L recirculating nft res last time and the one closest to the pump was twice the size and always much healthier. it caused the further plant to have deficiencies and had to put an airstone in eventually as the first one started stealing all the oxygen aswell. im asking this as you sound like you know this pretty well and im always looking to learn. but how do you deal with this happening in this system? are the first 2 plants not gonna be much bigger? also ive just noticed, your return pipe should be at the opposite end of the tank to ensure more time for mixing into the feed comming down and the contents of the res before getting pumped back onto the plants. again mate im not trying to be cheeky or that i just generally dont understand why these systems would be of any benefit other than cutting down man hours. sorry if that sounds a bit abrupt mate, just read it back. i dont mean it that way its just me lol. im quite direct when im curious i cant help it lol

The way these Current Culture systems are designed the circulation is very good. The pump dumps into the epicenter where it then goes to a manifold that splits it between the two rows of pots. There is a manifold on the other end and the pump draws from the middle of it, back to the epicenter. Each bucket, as well as the epicenter, have their own air manifolds. So each plant is getting about the same amount of oxygen. The whole system, in my case 50 gallons, is circulated 7 times an hour. I see no difference from one plant to another growing clones. This pic illustrates the flow.

What you described sounds like you weren't getting sufficient circulation and perhaps not enough air.

 

[EvilScotsman]

The way these Current Culture systems are designed the circulation is very good. The pump dumps into the epicenter where it then goes to a manifold that splits it between the two rows of pots. There is a manifold on the other end and the pump draws from the middle of it, back to the epicenter. Each bucket, as well as the epicenter, have their own air manifolds. So each plant is getting about the same amount of oxygen. The whole system, in my case 50 gallons, is circulated 7 times an hour. I see no difference from one plant to another growing clones. This pic illustrates the flow.

What you described sounds like you weren't getting sufficient circulation and perhaps not enough air.

ahhhh there you go mate. thats what ive been missing. i
thought recirculated meant it went in a single circuit through the system then came back to the tank.
sorry, im a bit slow sometimes.thanks tho man, that makes a lot more sense now. i did say im still learning lol and always appreciate the feedback. im only just getting to grips with all the different grow methods available. i just bought the most expensive 1mx1m kit on a certain site (got hit with cheapo, shitey nutes) and hoped for the best.
also, i did add a small 2w airstone halfway through the last grow but that was it....
can you imagine what wouldve happened if id got it right though? i entirely lost 3 weeks growth at the start due to noob issues and had to chop a full bag of leaves off every other day for 2 month, including over 20 colas. the other side looked the same.
400g from my first attempt in a 20L res tho, not bad going. 100 was deemed popcorn that i used for hash but the other 300g was pretty good quality bud. again, im really not being cheeky mate. im scottish its hard to not sound it, but can you get that from each res? it just sounds like an aweful lot of wasted energy, nutrients, space and money to me. 50 gallons is 20 times what i used so uses 20 times more nutrients, water, time and a whole load more power.
to be space/yield/hundreds of pounds worth of nutrients efficient per metre, in relation to mine would be about 15 times more light. those roots barely hit 10% of the resevoir aswell so i wont even count the fact that theres 20 times more root space in your set up. i realise mass production uses exactly what your telling me about but can it really be a more efficient way than this?

 

[EvilScotsman]

i swear i really dont mean that in a cheeky way mate and wouldnt like to cross wires. ive just read it back and honestly its just the way i sound. i am genuinely on my second grow and just trying to learn man. im a bit of a sarky by nature though so its hard to drop it when typing lol.

 

[EvilScotsman]

just realised my pump is only about 10L per hour aswell.....
if even that......

 

[Muddy]

ahhhh there you go mate. thats what ive been missing. i
thought recirculated meant it went in a single circuit through the system then came back to the tank.
sorry, im a bit slow sometimes.thanks tho man, that makes a lot more sense now. i did say im still learning lol and always appreciate the feedback. im only just getting to grips with all the different grow methods available. i just bought the most expensive 1mx1m kit on a certain site (got hit with cheapo, shitey nutes) and hoped for the best.
also, i did add a small 2w airstone halfway through the last grow but that was it....
can you imagine what wouldve happened if id got it right though? i entirely lost 3 weeks growth at the start due to noob issues and had to chop a full bag of leaves off every other day for 2 month, including over 20 colas. the other side looked the same.
400g from my first attempt in a 20L res tho, not bad going. 100 was deemed popcorn that i used for hash but the other 300g was pretty good quality bud. again, im really not being cheeky mate. im scottish its hard to not sound it, but can you get that from each res? it just sounds like an aweful lot of wasted energy, nutrients, space and money to me. 50 gallons is 20 times what i used so uses 20 times more nutrients, water, time and a whole load more power.
to be space/yield/hundreds of pounds worth of nutrients efficient per metre, in relation to mine would be about 15 times more light. those roots barely hit 10% of the resevoir aswell so i wont even count the fact that theres 20 times more root space in your set up. i realise mass production uses exactly what your telling me about but can it really be a more efficient way than this?

No problem, I get where you're coming from. You could build a system like you describe but it wouldn't be quite as efficient as the way CC does it. I built an rdwc veg system where it goes through all four 14 gallon totes, then through the filter, pump, chiller and back to the system. It works fine but I'm only vegging in it for a few weeks, so the roots aren't huge by then.

I'm averaging between 5 - 5 1/2 oz. per plant, depending on the strain. That works out to about .7 grams per watt of light. The holy grail is 1 gram per watt. My numbers have gone consistently up so maybe one day I'll hit that mark. rdwc actually uses less nutrients because of the high aeration. I rarely get over 400 ppm and my current Deep Cheese grow never got over 300. At peak feeding I give around 120 ml of my A and B base nutes, plus supplements to reach those levels. I only change the solution every 3 weeks, so the nutes go along way. You're likely to get those bigger numbers from the bigger totes. In a 20 gallon I would expect you to have around 15 gallons of solution. In my 8 gallon buckets, I have 5. So you're got a lot more room for a bigger root system that I do.

That was still a pretty good harvest given the issues you had. Every grow will get better as you learn.

 

[Muddy]

i swear i really dont mean that in a cheeky way mate and wouldnt like to cross wires. ive just read it back and honestly its just the way i sound. i am genuinely on my second grow and just trying to learn man. im a bit of a sarky by nature though so its hard to drop it when typing lol.

We're cool.

just realised my pump is only about 10L per hour aswell.....
if even that......

Current Culture recommends .75 liter of air per gallon per minute. Anything over 1.5 can cause problems, so more isn't always better.

 

[EvilScotsman]

ahh, see mate this is why i ask silly questions. some very sensible responses there thanks for that : ) i actually came across someone using something similar the other day and all i could say was WOW!. it shut me right up lol. poor guys tent was about to burst. thats some impressive stats with the nutrients aswell. i thought itd just be guzzln gallons of the stuff. your last point there though is something ive been trying to find out for aaaages! that nobody seems to know. 0.75 litre air per gallon per minuit. is that for that system or a generalisation for most hydro methods? got a 10L dwc that will be 20L soon so been trying to find out what the optimum range is for it. most say more is better but im sceptical