How to keep PH levels steady for marijuana grow

A question from a fellow grower:

any suggestions how to keep PH steady? I use AN nutes 3 part 2 week seedling, DWC waterfarm 1 plant 400W hps.

Also I fert with 400ppm solution(includes tap water 200 ppm) 1-1-1 3 part AN. But PH is not ‘steady’ although i PH it 2 times per day…

What is the starting pH of the water? I assume you are adjusting the pH to 5.8 as it is DWC. What are you using to adjust the pH? A commercial pH adjuster? How do you adjust pH? Do you mix your nutrients first in a separate container and then give it a little while to “normalize” before adjusting pH and then only after everything has settled for a little bit, only then place it in the DWC reservoir?

Update from the grower:

Ok first of all, before i planted the seed i soaked clay pebbles,air stone and pieces of rockwool(clay pebbles-rockwool in a proportion of 90-10) in a weak 3 part solution of ph 5 of GHE phosphoric acid solution (and kept it there as much as i could for approximately 10 hours).After i have finished with that i filled the hole of the rockwool cube with soil to make the seed sprout…After the seed sprouted in two days i transferred it in the waterfarm, with a fresh PHed solution of 0,7ec(i use to mix nutrients in a seperate bucket, let it sit for a little bit,PHit and finally pour over the hydroton mix).Now the following two problems occurred and they still exist: The first two to three days i watch PH and adjust every 6 hours, with thats beeng said its four times per day for the first three days, then it stabilizes somehow(my water is much about 8,3PH with colour drops used to measure it), and secondly my ec shoots up from 0,74 to 0.99 EC in 48 hours(its the PH solutions phosphorus that increases ppm). I run 18/6 light to dark, my temps of the water are 19C to 22,7 as the bulb warms up.The growtent and the environmental temperature of the room is 22,3C lights on. Idont want to leave unmensioned that i cover the waterfarm with a peace of materiar that is used to make bags for keeping temperatures cool inside and that i really know how to use those PH drops…

And as you can understand it is impossible to make it 5,8… it needs constant surveillance, so i simply drive it to 5,5 and let it drift to 6.
any tip is always welcome, i personaly think is a water problem. PH to hight…

I have heard some types of rockwool can raise pH, I don’t think this is a problem with most rockwool specifically made and sold for hydroponics. Using hard water can also contribute to problems like this as well as the type or brand of nutrients you are using. I assume you are using GH nutrients as you are using their water farm and their pH adjuster and so this brand of nutrients shouldn’t be contributing to the problem. I would invest in a digital pH pen, they aren’t that expensive on e-bay or the like, you might need a more accurate way to know more precisely where the pH is actually at, maybe it isn’t getting as far out of range as you think. You shouldn’t have to be adjusting your pH every 6 hours. It is ok to go through a range. 5.8 is the target and it can range anywhere from 5.5 to 6.5 without any real problems in hydro.

I think I would consider investing in an RO(reverse osmosis) filter. I used AN 3-part when I first started growing years ago. If you have 200ppm tap water, it is doing to cause your PH to fluctuate. Even if you use a pro ph adjuster, you will have issues.

With RO water; you can maintain a consistent pH using 3-part, and a pro ph adjuster. That is your issue.

X2 on the pH meter. I survived, barely, on drops growing in soil. When i moved to hydro the need for further accuracy was evident. The meter helped huge.

I am wondering if you ever solved your PH problem. I am having the same problem, my PH keeps creeping up and i cannot seem to keep it at a constant level. Does reservoir water temp have an effect on PH?

Numerous things can contribute to pH. And yes temperatures outside ideals can contribute to pH beyond all the normal things that might contribute to changing pH, the plant itself can change the pH due to its own activity during various periods of growth, and a high temperature could contribute to other things growing fast, like algae or unwanted microbes in the soil or reservoir that by growing fast and using nutrients and producing byproducts could quickly contribute to a changing pH .

Having a larger reservoir to the size or number of plants can help slow pH drifting due to the plants’ biological activities, because they’d have to use a lot more nutrients and contribute more to the ionic exchanges at the roots.

Hope this info helps,


This I’ve encountered numerous times over the years. Vpd solved this little mystery for me. If the environment is too dry the plant will take more water than nutrients from the solution thus the solution will rise in ppm/ecand the ph will drop.
Allot of folks (including me 20yrs+ exp, until this last year) don’t reach the level of understanding vpd. We wonder why year after year of learning and following these damn rules, we should still be struggling with issues at all. We work hard right! So look into vpd and every rule you learned over the years is correct and will fall into place like a well built puzzle, promise