How can you keep fish tank water cold?

If your aquarium water is consistently too warm for the species you are trying to keep, you can buy an aquarium chiller. These devices cost a fair bit more to buy than a heater, but not that much more to run. The main disadvantage of chillers, other than their expense, is that if you cool the water by more than a few degrees condensation will form on the outside of the glass. Don't use a wooden stand or a stand made of metal that might rust if you are planning on using an aquarium chiller.