Hillbilly5000 said:

So the common understanding seems to be that ph should be 5.8.
How ever this chart says 5.2 is the best.
Which one is it?



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I think what they're pointing to is maximum ion solubility for those micronutrients and it's correct, but not ideal for plant uptake. Cal and mag uptake become destabilized below 5.5 and at 5.2 would be largely locked out.

Your best uptake isn't going to come from a fixed pH value. We tend to settle on a fixed pH value that will allow the best uptake and it's not the same thing. The best uptake is going to come from a pH environment that drifts between about 5.2 - 6.3 strategically and at different times to get the best uptake of the nutes it needs, when it needs them. Until you are ready to tackle that beast, just aim for 5.8.

Hillbilly5000 said:

So the common understanding seems to be that ph should be 5.8.
How ever this chart says 5.2 is the best.
Which one is it?



View attachment 2633014

Click to expand...

Generally, I aim for 5.8 to start and let it drift slowly up for a few days until it reaches about 6.25. Then I pH Down back to 5.8 again. This, from what I understand, allows the plant to go through its full range absorbing various nutrients at various pH levels.

5.8 is the number I’d use as the home base, not 5.2. That chart is looking more at nutrient availability in the solution, but the roots still have to actually take those ions up without getting stressed. In DWC, parking the bucket down around 5.2 can make calcium and magnesium uptake get weird pretty quick, even if the chart makes it look tempting.

A short dip into the low 5s after mixing isn’t automatically a disaster, but I wouldn’t aim to live there. I’d set fresh solution around 5.7-5.8 and let it drift up into the low 6s before bringing it back down. That gives you a wider window instead of trying to force one magic number.

If the pH won’t drift normally or it keeps diving, I’d look at res temp, oxygen, EC strength, and whether the pH pen is calibrated before blaming the target number. In water culture the root zone tells on you fast.