Looks like a MG. Defficiency to me. I had that problem but it can be common ou just need to regulate all your nutrients. Just give it some Mg plus from Botanicare is good, but any Mg nut would do the trick. Simply cut all the other nutrients out and use a magnesium solution with just water for a week. Your plant should use up all the Mg and balance itself out in about a week, then go back to regular watering just watch your levels and keep them from fluctuating.