If you run an air conditioner then it will be a lot cheaper to cool the entire house a little more than to run a chiller.
Often, just a fan blowing air across the water surface on the sump or display tank is enough to sufficiently cool the tank.
If your tank does heat up, be sure to not let the temperature drop rapidly after the lights go off.
Powerheads add a LOY of heat, run an external closed loop if possible.