A cal/mag deficiency can lock out P, K, and each other. I'd say you need cal/mag. I hate trying to diagnose by photos. The plant depends on Calcium and magnesium to take up Phosphorus and Potassium. Nutes are SO inter-dependent on each other and dependent on pH it'll give ya a brain ache trying to figure it out.
I DO check it and rule out pH tho.. even in organic soil which doesn't really drift. Just to be safe.
Blaming everything on pH without checking is just really saying "I don't have a clue whats wrong"
suTra, my first few grows I had a chronic cal/mag def that started out just like that. (I listened also to those who told me I had to use RO water) I listened to the pH blamers and lost most of the crops to it. It only took me three grows to figure THAT one out!!!! Hopefully, this one will figure ot out just a bit sooner!! LOL.