Dang it Krish, STARTING TEMP is 81.6. That is the problem.
I cant tell you what to do. There is something else wrong. The stinking thing was 86 BEFORE you put the halides on. The house is 72. What in the heck is adding 14F above ambient?
Look we have almost identical systems.
I have
Sedra 5000 running the skimmer
Quiet one 6000 running the return.
Hagen 40 running the phos reactor
Two Tunzes 6100s running the flow.
A clip light with Lukes grow bulb on it
Two 250w MH Icecap With THE BALLASTS UNDER THE STAND.
I use two clip fans blowing on the water surface to cool the tank.
Its 71 in my house.
My tank was 79.7 when I got up this morning. Lights came on at 7am. Its almost 3pm now (7.5 hours later)
The tank temp is now 79.9 It will be 80.1-80.3 when the lights go out tonight at around 10 pm. ( I know thats a stupid long photo period. I like it. So blahhhhh.) LOL
Dude look think about it. If your room is 72. And your tank is 81.6 with the lights off. How much energy does it take to heat 75 gallons of water 10 degrees. Its a stupid huge amount. If it was your lights the temp would be closer to room at night. That shouldnt be it. Again I cant tell you what to do, I do seriously recommend backing up. Stop moveing your fans around. Figure out where the 10-14 degrees is coming from WITHOUT the MH running.
I dont know any nicer way to put it. It seems to me your killing yourself, trying all kinds of different ways to do the EXACT same thing. Move hot air out, move cool air in. The easiest way to do that is take advantage of how air naturally works.
I hope I am not coming across as mean or anything. Its not to toss you under the bus or anything. I dont want you do be all pissed off, aggravated, and drill 30 stinking holes in your canopy.
I will shut up now. I believe you should do what you think is right. Damn it stop and think. Your sharp as a tack. You know your system better than any other human on the planet. Relax, think about it, and let your brain go to work.