I have a 40 gallon tank. I use a uth, 100 watt che and a 60 watt bulb to keep it right in my home where the temp stays at 68. I do not have them hooked up to a tstat. Instead I control them by keeping them on lamp stands. Being my house is a steady temp I just raise or lower them to give the desired temps. I have done this for years. Once you get them dialed in they don't need adjusting unless you change the room temp.