Yellowing, wilting, stunted growth

Guarantee it is too much light and they are stunted. I rarely diagnose with extreme confidence, because this is often more art than science with indiscreet causes for visible symptoms, but this one is incredibly obvious. I can tell be the growth pattern this plant was given way too much light too early and it is stunted. See how close the growth nodes are together? all the leaves are originating from a very small length of stem. some are worse than others, and looks like some differences in ages. You need to ramp up the light early on relative to how the plant is growing... you'll quickly be up to full power (35-40 DLI, i hope) within 1-2 weeks, but if you blast them too early they willg et stunted. The look of th eleaves is a tell-tale sign. Then, as it progresses the paling is another symptom as the leaf cannot keep up with the amount of photons absorbed. so, back off the light for a bit.. wait to see a change in growth patterns -- this may not be uniform. You may need something to elevate the plants or a 2nd light etc to avoid one plant snapping out of it much earlier then the rest, waiting for the others to do the same, then the one that was quick about it gets all lanky in the mean time. -- anything to help adjust the intensity of light per plant will help. a little shade for a few hours etc.. doesn't have to be a plant elevator. I'd get the growth back to normal before tweaking your fertilizer or anything else. Always good to ensure pH is in a proper range with hydroponics. If you ever experience pH drift, buy better fertilizers. Shouldn't happen.