My local petstore keeps a variety of frogs in one tank and the guy there told me i should be fine mixing treefrogs. I have 5 treefrogs in a 20gal tank with a cage topper doubleing the space. 2 big eyed treefrogs, 1 whites treefrog, 1 dumpy, and an australian whites trerfrog all happily living together with plenty of space and places to hide. i put about 3 inces stone gravel and fill it with 2 inches water and flush it every couple weeks. I placed an airstone in the center so frogs can collect the moisture. This setup has required the least maintenance for me given the buildup of mixed species poop. I plan to add a couple more frogs soon. Good luck :-D