[alazandv]

You can place fans blowing across the surface of the water. This will lower your water temperature by about 2-4 degrees. This process is called evaporative cooling. Remember the word evaporative as it does exactly that, this metod works great but you'll need to top off water more often. While not a big problem in freshwater setups, saltwater tanks (depending on the size) will require you to stay on top of topping off as not to affect water salinity.