We had a turtle tank about that size ! Still trying to get grass grown in the bare circle . I'm thinking wire wheel or buffer motors , but I have enough of them . Or , an electric scooter , which I would be fine until the extension cord ran out .
FWIW, we had two single phase 220v 2-speed pump/motor combinations that came out of an old spa we never used. I took the pumps off and sold them on Ebay.5 . Can't let them get into the dumpster . Too good . 2 are single phase , 3 are 3 phase . Any ideas on what to make with them ? 3/4 and 1 hp .