You have to keep watering rockwool if your going to grow trees in them, or you PH will be all over the place, then you get the crazy leaf patterns like yours, it's quite a small area block wise for such a big plant, bit like the limitations on the solo cup challenge, only so much root space to pick up nuits.
Your leaf symptoms are the result of root damage caused by fungus gnat larve. Mix up a dilute solution of hydrogen peroxide and apply it directly to your cubes (slabs included), after a few minutes (10-15) you'll see the tiny larve working up onto the surface of the cubes/slabs. Reduce watering and/or improve drainage to correct this issue. Best of luck, Rockwool is a pita in the beginning
Hold up!!!! Are fungus gnats a common problem in RW?! I am switching from coco to RW because I just couldn’t handle the gnats anymore. Everything was clean until one bad batch brought in gnats, then they multiply so fast it was impossible to get rid of them. They got so invasive that even my aloe plants in my house had gnats. I had to shut down the whole garden to get rid of the gnats. I tried everything from covering the top of the pots with a layer of sand(read the gnats couldn’t get through it to lay their eggs in the coco) to applying a LIBERAL layer of neem meal on top of each plant to hydrogen peroxide. It slowed them down a bit but never actually got rid of them.
How much runoff are you getting? Maybe too much? Also leafs sometimes seem to do this on the beginning of flower so maybe some pruning will help you out here. You should be shooting for 120ppm of nitrogen for both veg and flower so if you have that then I don’t think it’s too low n but something could be locking it out. Also I don’t think they are root bound especially if you’re feeding multiple times a day, you can grow giant trees in a 6” cube with no root problems. Maybe you’re overwatering a bit, which may be killing the feeder roots which maybe is causing some root bound issues? Also did you say you’re feeding at night? That might be a source of the problem unless I’m reading it wrong(which is definitely possible)