I hate when people say THIS is your problem. So ill give my opinion. I recently ( last week) had the same issue, and couldnt figure it out. I religiously check my ph but once its set and i will not touch it til feed, i didnt check it.. But i use airstones..... It woukd raise my ph over noght or even a couple hours to 7.7!!! Long story short i was obviously nute locked.. I gave then 2 flushes and in a week they look awesome again. If you look at your branches, notoce how they look skinny and not much growth? If i had to guess id say flush them, and look at them in 24 hours and say WHOOOAAAA