Join Date: Jul 2010
Location: Outside Philadelphia, PA
The heater may not be costing you as much as you think. While they do consume a lot of power while on, they may be on only 20% of the time. It will be just enough to sustain the temp required.
Two other things you can do.
Check all the other aquarium related electrical items. The filter, lighting and anything else can also use quite a bit of power. You may be able to do an upgrade, and get additional power savings.
Insulate the tank to keep the heat in. Typically this is done by using thick styrofoam sheets to cover the sides, back and bottom, and using a glass cover over the tank. This can help retain a lot of heat.
Lastly, just because you think it's the aquarium doesn't mean that there are not a lot of other contributing factors. Check them also.