The care sheet from Understory recommends a 20 gallon for the adults. I haven't bought the tanks yet so I'll see how active they are and adjust accordingly. I agree about not making the tank too big sometimes. My baby red eyes had to get over an inch and a half before they seemed comfortable outside their small enclosure. It almost seems like they get lost if the tank is too big. The big question now is how should I heat the tank. What is most everyone doing out there? John suggested it might be dangerous to put it under the tank even if the substrate is raised I'm assuming because I was planning to have a little water down there. Could the glass crack? It doesn't feel hot enough to do that but I've also never tried it over a period of time.