I just put my African Dwarf frogs in their tank today. I turned on the heater I bought but when I looked at the thermometer it was 84 degrees. So I turned the thermometer off and the tank is at 80 but I'm worried that the temperature will drop over night. What temperature is too hot and will harm them? I don't want to kill winkin, blinkin, and nod when I've only had them for a day!