How big IS he, exactly?
I keep African Dwarfs, I'll tell you that straight off. They're comparable, but the African Claweds get much, much, much bigger, so I'm not as well-versed on them as I am on the ADFs.
I think two feet for a very small frog, though, would probably prove to be an enormous problem. Would it be possible, then, to set up a 10 gallon tank just for the frog? It may be necessary if you see him struggling to get to the surface.