Just to confirm, it is an African Dwarf frog, not a Clawed frog? The later will make mixing difficult, and it is important that you tell us accurately. The latter have clawed frong feet, the dwafs have webbed feet
How are you planning to cycle? Remember that leaving the tank to sit is doing nothing toward cycling. [topic="113861"]This thread[/topic] will give you the correct methord of cycling, that myself and others would higly recoment you follow. The two main advantages of this type of cycle, is that there is little work, and no risk to your fish. The methords of cycling usualy outlined in tank documentation usualy put the lives of the fish at risk, in the hope of increasing sales
For dwarf frogs in a 20g, and colourful, you may consider neon or cardinal tetras. The latter are more hardy, but both can be sencitive. There are a multitude of tetras out there,, many of which would be ideal candidated. The best thing you can do realy, is have a look arround your LFS, and come back here with that list, so that we can say what is most compatible. If the frog you have is a clawed one, the only thing you can realy mix with it in that size tank, would be other clawed frogs
HTH
Rabbut