Aquarium running hot

My aquarium temp generally sits around 79 degrees, but yesterday I noticed that it reached a high of 82 degrees, and first thing this morning (before my day lights turned on) it was running at 80 degrees.  The room temperature where the aquarium is located is a pretty constant 72 degrees.  Anyone have any ideas on what could be causing the temp increase?  Also, how worried should I be about 82 degrees?  All my fish and coral look great, but I know that 82 is too high.  I'd really like to avoid buying a chiller, but I'll get one if absolutely necessary.

Have you cleaned the pumps recently? If not you might try cleaning them out and inspecting the impellers. Sometimes debris can get stuck in the impeller space and cause extra friction so the pump heats up. Usually the pump is louder when this happens though. Just a thought...

Phishin801 wrote: My aquarium temp generally sits around 79 degrees

I run my tanks at 70-75 degrees, giving some safety margin for an unexpected increase. 70-80 is the range.

As the outside weather warms, aquarium temp will rise slightly, even with AC running because most tanks are next to a wall where the temperature of the wall inhibits cooling in the summer and heating in the winter.

I agree with what has been said regarding pumps and evaporation. The ocean is not closed up. Neither should our aquariums be closed up. It's remarkable how the general health of a reef aquarium increases when the top is raised up to expose the entire water surface to fresh air. Even just lifting the lid one inch can make a significant improvement in healthy pH, not to mention the cooling effect.
Otherwise, add a good fan in the lid blowing onto the water.

I too have been leaving two windows open all night. Cool fresh air - Ahhhhloha

My 3 cents:
1. Place the fan pointing directly down into the back chamber.
2. I have found that there are ways to set up a tank and to aquascape so that fish don't feel the need to leave the water or don't get frightened to where they swim fast up the glass and inadvertently leave the tank.
3. There is also an inexpensive clear screen material (~3/8" mesh) that many hobbyists here use to completely eliminate the worry.

Aloha