The Reefkeeper Lite is an awesome temperature controller. I ran one on my 125 for a couple of years ( until I sold the tank ). I had it controlling 2X 200 watt heater plus a fan.
If the temp dropped below 78 the heaters came on. If it got above 79 the fan came on. At 81 the lights would turn off.
Plus I used it as a timer for the lights and a PH monitor. Well worth the investment.