It Doesn't seem Like lack of nutes to me at all, as the damage would look much worse in my humble Opinion!! My diagnosis will remain Sun Exposure! Keep Doing what your doing! If you do decide to use any kind of bloom nutes they will be very high in P & K the analysis will look something like 0-50-20 This is what you will want when they show signs of flower!! Which is more than likely right now!! (Yehaa). Follow the label and dont over feed! Otherwise Cheeb Im quite jeleous of your girls!!! I may even Love them!!