Colum Black-Byron wrote: I thought magnesium deficiencies was when the veins were green, but the rest of the leaves were yellowing off. The leaves in the background on the first picture look identical to that. As does Potassium deficiency, and a number of others. In the early stages Potassium and Magnesium deficiency will show almost identical symptoms in most plants, and both show on the older, lower leaves, as both elements are mobile within the plant.
Potassium deficiency is far more common in fruiting plants in AP. I've had Magnesium deficiency only once in over five years and a number of systems, but I've had Potassium deficiency a few times. When my system did have a Magnesium deficiency it showed as similar yellowing to these pics, but with many small dead/necrotic patches between the veins also. It may well be Magnesium deficiency, but I would wait for up to a week after adding the Potassium, to see if there is any improvement, if there isn't, then maybe try Epsom salts.
Colum Black-Byron wrote: I read somewhere that too much light can cause leaf curl like in first picture as well, but I've never used lights, so I'm not 100% sure on that, there are a few other things that can cause leaf curl as well. Too much light and/or heat can cause leaf curl, but the leaves will be perfectly healthy and formed, just rolled up at the edges, and they will unroll after the lights go off each day. Plus, it will be the leaves closer to the light/heat source, so the top leaves. Whereas the top leaves on some of these plants are fine, while leaves lower in the canopy are rolling or cupping. It's the newer leaves on the affected plants in these pics are deformed and hooking down at the tips, and some of the older leaves are cupping, classic symptoms of Calcium deficiency.
There is definitely a Calcium deficiency in this system, and either a Potassium or Magnesium deficiency as well. Potassium and Calcium are probably the two elements most commonly deficient in AP systems, especially when growing flowering/fruiting plants, so I would focus on them first. if you don't have any luck with the yellowing of older leaves, then maybe try the Epsom salts, but I would put them in the tank... and don't try every solution at once, or you'll never figure out which it was that solved the problem.
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