How precisely should I adjust the Ph in my nutrient solution

Nutrients
1

I’ve been using General Hydroponics PhUp and PhDown to adjust. In practice it’s generally PhDown, meaning it will be a bit alkaline before any adjustment. As an experiment I mixed 6 five gallon bottles of unadjusted nutrient solutions. Then I put 4ml of PhUp in the first, 2 in the second, nothing in the third, 2 of PhDown in the next, then 4 then 6. I used an aquarium air pump and an air stone for agitation and let it sit for 15 minutes to stabilize. I measured the Ph in all the bottles.

I used an Apera GS4 for my measurements. I just replaced the probe about two weeks ago and I calibrated it against all three calibration solutions.

It looks to me that for my nutrient solution, 1ml of either PhUp or PhDown moves the Ph of a five gallon bottle by about 0.3. Since I was using 2ml differences I got actual Ph differences between the bottles of about 0.6.

The last bucket (using 6ml of PhDown) didn’t move it quite that much, so I think there are diminishing returns as I get far from a Ph of 6. By that point my Ph was about 3.5.

When I feed my plants, I generally shoot for between 5.8 and 6.2. If it’s above 6.2 I try to nudge it down and below 5.8 I try to nudge it up, but within that range I don’t bother. I have a feeling measurement inaccuracies are going to make it hard to adjust closer than that. I’ve never had to use more 2ml in a five gallon bottle to get within that range. Usually it’s 0 or 1 ml.

I guess my question is, does this all seem normal? And is a 0.4 target range for final Ph OK, or should I try to dial it in closer?

2

I feed in the same range, 5.8-6.2 in Promix. You don’t have to hit the numbers dead on, you’ll go crazy trying. Keep it in a small range and the variance won’t matter. :oncoming_fist:

3

I think the more you move it the more it will take to continue to move it. Not a situation where every ml of adjuster will continue to increase or decrease the solution the same amount. There is probably a name and explanation for it but I never chased it down.

4

Thank you both!

If I understand this stuff, I did something useful to me but not extendable to anyone else. I had been going totally by trial and error adding PhUp and PhDown and I wanted to get some idea of how much to use. But AFIK, it depends on what else is in the solution and if what is there acts as a buffer or not. So the 0.3 I see probably won’t be what anyone else sees. The reason I couldn’t find any guidelines is that they don’t exist.

I think it was useful information for me. Unfortunately adjusting Ph is more complicated than it looks at first glance. It’s very helpful that I don’t have to be super precise.