Hydroponic leaf problems - 6.2-6.4 ph. Humidity 75-85% early-middle flowering (I can't lower the humidity). PPM 750-780. Tap water was 140 ppm. GHE fe

What else are you feeding them? Might be more clues in it from there. I think you could lower the PH a bit in hydro, and RH is a bit to high. it could result in bud rot in flower. Hopefully it changes soon, if not grow more airy stavias and keep up the airflow. Get some runoff when feeding to prevent buildup that could cause a lockout and might be part of it. https://420life.com/wp-content/uploads/2021/10/Marijuana-Leaf-Deficiency-Chart-scaled.jpg This leaf chart might help yea. I see tip burn on some of the lower growth in the background on the pics. So maybe to much. Mesure the runoff PPM and see if maybe you need to flush to fix the medium. convert PPM to EC. most places in the western world use the scales 500PPM=1EC. 1EC=1EC no matter where your at, so it makes it easier to understand. Some other places use 700 or 620 PPM = 1EC