78 - 81 during the summer with no chiller. A small fan blowing on the water's surface really works wonders to stablize temps. Right now it's set to run every other hour when the lights are on. On really hot days, I just set it to run more frequently. FYI I have a 24 g. Aquapod with the 150 MH, 2 maxijet 1200s and a rio hp running the skimmer.