I recently set up a 75 gallon reef tank with some SEIO 1100 powerheads, skimmer pump, 650 gph external pump, T5 dual actinic strip and 2 150W MHs. My home is Air Conditioned so you wouldn't really think that heat would be a large issue. It would get up to 87 degrees at times though, and it may have gone higher than that, but I would turn the lights off to try to reduce it once I would get over 85. After getting a chiller and having it fail due to shipping damage after only a few days, I went to Walmart and got a 7" clip on desk fan. This was to help cool the tank while I waited for the new chiller to come in.
After running the fan blowing over the surface of the tank for less than a day I realized that I wasn't going to need the chiller at all. I canceled the replacement order and returned the original chiller. Saved a ton of money. This little fan keeps my tank less than a degree higher than whatever my A/C is set on. Since I am usually around 77 to 78 in the house, my tank stays pretty consistant near 78-79.
I do evaporate more per day now. Thats okay with me though as I drip kalkwasser to help eleviate a depressed pH in my tank due to CO2. Now my tank is cool, I don't have the chiller electrical costs or initial buying cost, I bought more livestock AND I get to drip more kalkwasser which keeps my pH right around 8.0. I couldn't have planned it better.... really, I couldn't