I'll try guppies, then. Hopefully, they can help clean up the tank a bit every now and again. It'll be really neat because it'll be a whole ecosystem in itself, the frogs, of course, being at the top of the food chain.

Yeah, my sister has a ghost shrimp in with her goldfish. From what I can see, they appear to have tough exoskeletons, and that might not be good for digestion. They're also very small, so they'd have to go as cleaners and only cleaners, though they do do a good job at cleaning. I might try red shrimp, I think they're bigger.