First thank you for the help

The room I keep my frogs in is a small computer room off the living room. We live in a very old (160 year) house and this is the only room in the home that keeps the tanks away from the outer walls of the home. The room temp is about 20 c in the day 18 c at night, and least drafty. I have started this undertaking with a 18x18x24 exo terra. It comes with the normal screen lid but prepared to have plexy glass cut to cover half the screen to help keep humidity and heat in if I need to.

I am most intrested in getting two dendrobates auratus (I hope I spelt that right lol)

I'll try to add a photo of the tank so far, keep in mind there is still alot of work to do with it lol
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As you can see I still have alot of patching and other work to do but I want to figure out this water heater idea first.
Thanks again for the help.