I don't know much about the frog in your tank, so you'd have to run this my someone more knowledgeable, however Otos (Otocinclus) might not be a bad idea. They're small, and they stay small... They are peaceful (this is where the frog might be a problem if it's aggressive) and they do a pretty good job with algae. If you do consider getting otos, keep in mind the do better in a group of 3 or more.