What kind of filter do you have? If you have a canister, consider a longer outflow tube from the unit and put several cooling packs around the tube. Wrap them up in paper towels and aluminum foil to insulate and turn off the heater. Of course, you'll have to change out the packs every now and then. Also, put in some air stones and crank them up. Leave the hood off/open for evaporation and cut the lighting to the bare minimum necessary for your tank.
