either your ph meter is no longer with us, or you got some root FUNK stuff going on like fungi or rot.
If that was a light issue it would only be happening up top, it wouldnt also be happening on your seedlings that are prob undr less tha 400ppfd, or the lower areas on the bigger plant. Period lol.
If you go 6 inches further from your average 100-150w led like you and me use, the intensity will cut in half or more.
i repeat this all the time too so might as well again. You do not have light related burn 2 feet from your 100-150w light down on the inside of a bushy plant, regardless what someone on the internet tells you. that isnt possible unless something else is WAY out of whack. It just isnt a thing that happens, ever, to anyone, in any context, at all period lmao. If you had light burn it would only be on the upper most leaves the way your tent is setup. It couldnt possible be down inside the plant too. And it would appear as chlorophyl bleaching before it actually damaged tissue directly, and that looks like magnesium deficiency, just up top where you normally see immobile nutrient issues, rather than down low where a mobile bnutrient issue like magnesium would actually pop up if it were a deficiency.
Inb4 someone pops in to tell me im wrong because they had "the same issue" and it "went away" when they backed their light off to the intensity i give my 3 day old seedlings

. Although that usually only happens in on-topic open forum below an OP question, not the trainwreck lol. You can make lots of things disappear when you back off your lights like that. One of them being grade A flower quality lol.
Creating a situation where an existing problem just cant express, to "fix it", is akin to drilling a hole in someone's head to alleviate their headache. Or tearing the fingernails off someone's hand so they dont have to worry about getting hangnails anymore.
In this context if you keep backing your light off you wont be solving any problems, you'll actually just be burying them even deeper under even more variables.