There's a couple of leaves like this on ma plant what's the problem found a leaf diagnosis page but there's a couple of similar looking leaves but they say its different things any help appreciated thanks. Growing in coco Temperature 25.8 600w hps light
Im no coco or hydro grower, but I think you should add cal-mag rather than cutting back on nutes. if it was nute burn, the leaf would be fried from the tips inward
actually I dont recommend you act on my advice in this case. it was just meant to hopefully simplify your research, not be a proper diagnosis
how old are the leaves that are showing necrosis? if they are down low dont worry about it. A product called vita max plus will provide all the micronutrients you need. looks like a magnesium deficiency to me, bring your pH up to about 6.3 and magnesium absorption goes way up.