All depends on what you intend to keep with your "cleaning" fish....For your size tank, I'd suggest go medium to small in which case 2 dwarf ottos will do the job. they are hardworking & should actually get a bonus for their worth.
Welcome to the forum
Raris. Hope you find the fish your looking for.
All types of fish
conditions
I looked at this web site. it has loads of fish. it tells you loads about the fish and the conditions the tank has to be in for the fish