One of the best algae eating fish (especially for a small tank) would be the otto catfish. It has little waste, unlike a pleco, and you would really only need one or two.
You should get algae eating fish only AFTER you see algae develop. The fish will starve without it. Well, no, there is another way but you have to buy sinking algae pellets. They work the same and the fish eat them it's just extra money though.