Week 4 in flower , yellow leaves

Yes 001 is right that is lockout Due to excess of N or Mg (or both) ur Ca, P and K is locked Most of leaves are droopy and curling down, also u can see rusty edgies and tips, purple petiole and Chlorosis like Mg (it looks like it, but it,s not it) Look at 3rd pic on the left dark green plant Mg excess, p,ca lock Ps u,re overfeeding em

it doesn't matter if one is fine. All that matters is a plant is having an issue and a tweak to the formula will avoid it next time... Are you religiously getting 10% runoff? If not, i'd wager that's what's going on... something builtup in the medium. Symptoms are abit funky and look more like trace element related and if that's the case, more likely lockout of some sort -- pH-caused or some other portion of nutrition is too high and locking it out. The other plants look a bit lush, too, so some overfeeding without 10% runoff could be the culprit. Dont let them sit in their piss, either. In a soilless context, you ensure to get a minimum 10% runoff to avoid buildup... it may rest higher than what you feed but it won't climb further. This makes diagnosis easier with one less potential cause. Better formulas work on a wider range of plants.. the esoteric stuff is what gives these plants a false reputation of being picky... usually self-inflicted as opposed to a picky eater.