Hm, Do you have AC
in your house/appartment? If you dont then one thing to know is that a chiller is basicly a small AC
unit for your tank and just like other AC
units they expell heat outward. The net result is unless you duct this heat outside it warms up the room the tank is in. Net result is a warmer than should be room.
There are many ways to keep the temperature down with out the use of a chiller. You could install fans above the tank blowing over the surface of the water. This will increase your evaportaion rate but at the same time cooling your tank.
The smallest chiller I know of is the ICE PROBE
That device should be mounted via a hole in the tank or in your sump. Also there is a temperature controller unit that is needed. Total cost from Petwarehouse.com is $150.00