in the house is set to a permanent 76-degrees. My tank heater is at 78-degrees. This morning at 6am I noticed that my tank temperature was at 79.7. I usually get less than a 2-degree temp swing from my lighting, which is 440 watts of VHO
and 39watts of T5HO over a 75-gallon tank with 2-fans in the canopy for about 10 hours. One fan blowing air over the tank the other blowing air out of the canopy. I just set up my tank last July and it was not a reef tank at that time. It sounds like I am still ok so far. But summer is still to come, its only May. It gets pretty hot where I live in Southern California.