Not what you want to hear, but my 93 cube with 120+ system volume, external pumps, and a fan on the sump with a 400w MH 12" over an open top will hit 83-84 easy in the summer if the chiller were off (ambient around 70 in the room). My chiller runs occasionally even during the winter with the tank in the basement and ambient in the low 60's That's keeping the tank at 77 though, it would likely run around 80 without the chiller in the winter.
I run a 120 volt computor fan over my sump 1 hour before the lights come on, and 1 hour after they shut off. I have my 2, 400 watters on from 12-9. My HVAC is on auto 24-7, never going above 76.......