It looks like a possible N with a Magnesium overdose...but actually I think the inner part of the leave is too green for Nitrogen def...Read up on Mag and Zinc toxidity, because when one element% is too high; Another is being locked out...Magnesium oftens conflicts with calcium...(good reason to use calmag+...perfect blend) goodluck...

I woulld lower my EC and by adding a fresh batch of light nutes...dilute your recipe by 25-50%