African Clawed frogs are great little creatures. I have had many. They do best with very large goldies I think. My one that I have now lives with my big comet, and shubunkins. He's hillarious. And yours may just eat your little fish in there. They eat anything they can get their mouth on. And don't let go once their mouth is on it either!! For instance, one of mine grabbed onto one of my fingers once. It took quite a bit to get him to let go. They eat just about anything. From reptile pellets, which is what I feed mine. The Reptomin for turtles. Or from time to time he gets chopped up earth worms. Each frog requires 10 gallons of water. Like in my 55 I have my frog which is 10 gallons there, and 3 goldies. Which is 20 gallons for the first goldie, and 10 for each of the others. Which puts me up to 50 gallons. So I don't think I'll be adding anymore fish to that, maybe one more frog, if I up the filtration.
But all in all they're great pets and get quite large. Females can get to about the size of your hand, well my hand atleast. And males stay a bit smaller.
If you have any more questions feel free to pm me.