Potassium deficiency?

Certainly looks like it's a potassium issue. I took a look at both your diaries (unsure which one you're talking about here) and I don't see any information on pH in either one of them. pH is usually the culprit when it comes to deficiencies here - but it could also be locked out by excess nitrogen and since I see you're using FF Grow Big in a fairly heavy-handed way, think this could be your problem. I used to use FF and it was my experience with Grow Big that made me quit using the nute line altogether... no matter how gently I used that particular nute, I always ended up with nitrogen toxicity locking out other nutrients... so check both - the pH and maybe look for signs of nitrogen issues, too. (And btw, each plant can react differently to the same feed/conditions/whatever - just need to treat them individually!) Good luck...