I have found that the temp of the room has a big affect on the temp of the tank. If i turn my thermostat down on my house by even 1 or 2 degrees, then my overall temp in the tank also goes down, so I have to set the room temp, then adjust the UTH and infrared bulb. I have a 40 gallon glass tank, and this is my setup. UTH and Infrared bulb are on the same side, so i set them where the warm ambient temp is around 85 and surface temp is 90ish. Then i have a warm mist humidifier setup next to the tank and funnel the steam to the top of the cool side. This keeps the cool side in the high 70's and the humidity right where it should be.