Only 1/3 of the bottom of the tub should be covered. I keep the hot side (bottom of tub) at 92 F, and the cool side around 80 F. The hide should be on the hot side, if you decide to use one. The water bowl should be on the cool side. I also suggest to use flexwatt as opposed to an under tank heater. Call Rich at Reptile Basics. He has everything you will need, including heat and tubs. If you plan on getting more than one ball, I suggest purchasing a rack system. This comes with tubs and heat. Hope this helps.