Turn your ac down? Change your lighting schedule to cooler parts of the day? Openening the feeder lid and increased surface agitation? I've noticed that with any amount of surface agitation the clear plastic shield becomes soaked so I have the lid propped up 1.5 inches. Its not as attractive but niether are dead coral. A chiller would be big money/ plumbing and not practical IMO. Is you tank sitting in front of a window/ Can you relocate the tank to be underneath the A/C vent?