I'm down in alabama, and we've been having near 100 deg days every day for a while, and my AC isn't that great. I've come home from work to find the tank REALLY hot! It tends to hover around 85 deg, but I've seen it get to 90 once. I've had two polyp bail-outs from the heat. My solution has been to put a 1 gal block of ice in the sump, just barely in the water, so as it melts it will cool the tank off. I've also shortened my photo-period down to 8 hrs on PCS and 6 hrs on MH. Lights are a huge heat source for me, 250 watt DE MH and 180 watts of PCs on a 29 gal.
Also I make sure the computer and all room lights are off before I leave. Esp the computer, a 450 watt power supply, even when just idleing will warm a room by a few degrees.