Wow, those ladies are beautiful. I just wish I would have found your thread sooner! I have a very similar setup right now, using ocean farm and FF nutes. I could really have used some help with my fox farm trio feeding as well. Mine are about a week or two from harvest and my 60-100x microscope is already on its way lol. I had alot of rusting/browning on lower leaves, worse than you did, but I think I over fed them. The buds are looking great, but the yeilds are quite a bit lower than yours so far.
Good luck, and I cant wait to see pics of next season.