If its any consolation to you, I have the same problem. I use two powerheads and when its really hot outdoors (Texas has 1 season..... summer and 12 weeks of bad weather) the a/c doesn't cool as well inside so the temp goes up. Mine has been as high as 87 last night. I raise the hood point a fan on it and it cools down. You might try keeping the front lid open (personally I don't like the evaporation or jumping wrasses,etc.), keep your lights on less hours of the day, or even switch the lighting schedule to be on when its coolest in the house(nocturnal). I believe the heat is worse on the snails and other inverts but the fish seem to handle it well and when I see the temp get over 85 I shut the lights and blow the fan over the water surface. I hope that helps. I am also trying a 10 watt submersible halogen lamp in the middle chamber as a potential refugium but when the temp hit 87 last night I'm thinking that may work best in the winter. Any additional comments are appreciated. Regards Jeff