Any experienced tree growers please help.

I have never grown in pots before. I have 42000 wt room, 20 horizontal 600 wats and 30 vertical 1000 watts. I am doing 44 plants that have been vegged for 6 weeks. Last crop in week 5 of bloom I turned digital ballast from 75% to 100%and around that time my leaves started yellowing and dying fast. I still don't know if it was too bright ( heat was nvr above 87) or If they were root bound or if it was rootrot. I have nvr had this problem in tables with only top lighting.Is there something different I should do with these trees In pots??I have co2 and intake out take ( on timer).I had a fungus gnat problem but in tables I had gnats before without this happening. I didnt know this system would work any differently.