Sick plant

I would recommend dialing the pH back to 6.2-6.3 tops and give it 1-2 waterings of just plain ph'd water. I have had this happen in the past with Coco and it definitely could be a build up of nutes near the bottom. In my 4-5 gal pots, I have taken 1-1.5 gallons to let it really flush out as much of the build-up as possible. One telltale sign is if you get a white salty looking build-up on the bottom of your pots. Try to put something underneath the pots as well. I use some cut-up pool noodles. This raises them off the ground allowing air to flow and draining to drip down and not to build up. If need be, use a towel to soak up and excess and the rest will evaporate. I hope this helps! 👍

I flushed her when there was N tox a while ago and about to be 3rd week into flower

Yea that’s one of my problems I don’t have good drainage so I do feel like there’s a build up

These are lower leaves and they don't heal. Flowering npk ratio is 1-2-3. Just focus on a proper diet, and development of colas. If anything it looks more like a potassium deficiency from discoloration and straight burnt tips. Also looks like you had too much nitrogen going in by the down clawing on the one leaf in pictures. The other issue might be improper run off caused this as salts built up in substrate. It's hard to say exactly with limited information.

Hows your watering? Keeping the soil on the dry side, or keeping the soil saturated all the time? How did you change your pH, did you do a flush with a different pH, if so, what was the new pH value and how big of a difference is it compared to the old value? By changing the pH do you mean the pH of what you are watering in, or the soil pH? Yellowing of lower leaves indicates Nitrogen, but Nitrogen deficiency usually displays as a leaf tip back yellowing which is uniform. Meaning the veins and the between vein tissues yellow evenly. Then after the leaf has turned yellow it can curl and die back from the tips, or serrated edges. When's the last time you flushed your medium, if ever? I'm not sure what week of flower you are in but if you are a few weeks from harvest then i'd just start to flush.

It seems to slow down. But I’ll be more sure checking on them today

As I see you are already way into flowering. It is quite normal to have some leaf symptoms on big fan leaves as in this phase the plants immune system is gradually lowering to concentrate more energy to flowers. I would not recommend any drastic moves. Keep monitoring new growth and bud development to see if any further steps required. Everything you do only takes effect later (and on new growth), so be patient. Let it grow and Good luck!

necrotic bits won't heal. yellow can 'fill' in again. this looks like sa nitrogen deficiency. pH in ranges you speak of probably didn't cause that. slightly acidic is better, but also N doesn't have availability problems just over 7. plant may decide to shed the leaf too... sucks it down and eventually falls off. so focus on bigger picture - did it stop spreading / proressing anywhere else?