About to switch to flower but can't figure out what's up with the plant on the left?

K-deficiency or locking out K. slightly overfed - look a bit too lush under grow lights, therefore even darker in normal lighting. The right plant seems to have the same thing? Is that what it looked like initially? if so, maybe a molybendum deficiency, but that would more likely be lockout. rare to have a physical deficiency with trace elements. symptoms are not discrete. you need more than that to confidently diagnose most problems. use any information you have to eliminate possibilities and try one solution at a time so you can learn something from it.

Might need a little more info? What are you fertilizing with? Got a runoff pH? Based purely on picture visuals is tricky. When water can't reach the leaf margins and interveinal areas first turn yellow(chlorosis), and then cells die, turn brown, and dry out (necrosis). It's a combo of factors, with environmental stress worsening underlying root or soil problems, water stress (drought, heat, wind), root problems (compaction, damage), and soil issues (salts, poor drainage, or potassium). Can't really be specific without your metrics, but often its a wonky problem with water transport or nutrient uptake. If it was nutrient deficiency and still a good pH then potassium would stick to its mobility by presenting symptoms on primarily old growth. If it's locked out, it would present across the plant or on new growth, then your pH might be skewed, or maybe you over fed cal mag recently, this could potentially antagonize potassium. options, options. gluck