I have a rheostat right now but I don't like it. Its not as stable as I'd like so I have another thermostat on order which should be here in a few days. I have an acurite in the tank so the main piece shows me my ambient temps which are about 80. I just don't want the hot spot to be too hot and I'm not sure where I should measure those temps. The difference between the glass bottom temps and the substrate surface temps are pretty big. So I'm confused by that part.