When I kept a heater I had a Titanium one with a digital temp probe, connected to my reefkeeper with its temp probe for dual redundancy. I had the heater on one side of the tank, and the temp probe from the heater about midway down the tank. I then had the temp probe from the ReefKeeper on the opposite side of the tank. The RK was set to turn off that outlet if the tank reached over 78 degrees, the same temp the heater was set at. I've since got rid of the heater and never had any issues that I can contribute to temperature. My tank will get up to 82-84 sometimes in the summer, and when I forget to close my porch door in the winter down to 65-68.