You're getting pretty far into flower and some yellowing is going to happen. It could be a PH issue but you're working to raise that, maybe you can leave the PH higher so you can raise it faster...? That's what I'm gonna be doing, but I'm in coco. I was checking some run off last night and I'm a bit low too, mid 5's. You can bump the nitrogen up a bit that may help or try floralicous, a 1/8 tsp for either per gallon.
Also, wanted to let you know I was talking with InTheShed about super cropping. You absolutely did right and again I want to let you I'm sorry. Any how, I did exactly what you did to my Northern Lights and she's bouncing back like a champ. I'll be damned!!!!!
Your plant looks great, keep bringing up the PH to around 6.2 -6.5 runoff. And think about a nitro bump or some Floralicous.
I PH every mix to around 6.2-6.5, and my runoff was at 5.3 last night. I'll correct it but worrying aint gonna do shit, so I just go one feeding at a time and give her love in between meals. Remember she's gonna eat some of her own leaves as they start to wither she's pulling the nutes back, wait till there dry and wrinkled, then pluck'em.
Not enough light gettin to those leaves maybe?
You're Cruisin!