Nutrient issue DWC with pic

ballpark PPMs N/P/K 120-140 50-60 180-210 Ca/Mg/S 100+ 80+ 100+ ymmv on these as hardwater will contain varying amounts.. my experience is with nearly too hard of water. 1.3-1.5 EC with proper ratios of components will keep nearly all marijuana plants happy... even when i have 7 different strains, they don't show any symptoms. But some combination of the above near the ratios given will likely work well and require minimum adjustment relative to your local garden variables that may differ from mine... if you find something you provide is significantly off from these values, it's a good chance it's part of the problem. 600ppm on a seedling won't cause damage or lockout on its own, neither will 700ppm concentration ... However, if some component is far out of balance it may be possible. which a 4-18-38 could easily be giving too much K, which could lock other stuff out in such proportions. i use something similar with jacks... do you have a cal nitrate and magnesium sulfate (epsom) part? use a ppm calculator at manic botanix and you can see waht you provide of each molecule... if you track that stuff and take notes, you will quickly hone a recipe that does not cause problems and more easily isolate what teh cause is of problems as you near that goal.

Nitrogen or some micronutrients—- if what you say is correct. Show the roots!