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 donāt think itās too low n but something could be locking it out. Also I donāt think they are root bound especially if youāre feeding multiple times a day, you can grow giant trees in a 6ā cube with no root problems. Maybe youāre overwatering a bit, which may be killing the feeder roots which maybe is causing some root bound issues? Also did you say youāre feeding at night? That might be a source of the problem unless Iām reading it wrong(which is definitely possible)