I keep my 250 MH's on my 155g and 175 MH's on my 58g 3" above glass tops with no problems, this way I light the tank inlieu of the room. To keep the tank and glass tops cool I have a 3"fan (58g) and 1-4" fan (155g) sitting on top of the glass tops to keep the aquarium's cool. My office is at 75 and the tank is 77.3 and at home the room is around 77 and the tank is 79