This is just a temp set up for my new adoptee until I get another 40 breeder but I was wondering if I can use 2 safely without cracking the tank. I have a 30-40 gal Zoo Med UTH that I'd like to use in place of the CHE I have. There is a smaller UTH on the other side. The instructions for the new 30-40 gal UTH states 2 should not be used on one tank, since it can crack. It would be used with a dimmer until I get another thermostat here shortly. If I kept it low enough, could I use both UTH's on the 20L? The tank is insulated with foam board but I'm also still concerned about the ambient temp. I was hoping to move my CHE to my other tank, the 40 breeder, since my ambient temp is not where it should be. I haven't insulated the 40 yet, but will be doing that this weekend. Any advice would be helpful, thanks!