Instead of doing just a water change to cool things down : I get more sand out of there instead of the water. I rinse the sand in treated water that's about 2-3 degrees cooler than the tank temp. It seems to help for cooling the tank a lot more than a water change. Also, floating sandwich size zip-lock bags, filled 1/3 or 1/2 full with water that's a few degrees cooler than the tank water. I float mine near the out-going filtered water flow, taped to the edge of the tank with duct tape. Most of my wet pets are afraid to go near them, so I haven't got any problems yet. But I'm sure some of you have pets that would probably attack any strange looking object that's put in their tank!, so you might not want to try this!