The snails you typically see at the pet store are called mystery snails, and they do eat algae. I had one with a betta in a 3-gal and that worked fine for algae, but if you have three sections you would not want to get three of them, as snails are HUGE waste producers and you would be doing daily water changes (if that is what you do anyway with your bettas then no prob). You also will most likely wind up with millions of baby snails, too, which sometimes can be a nuisance. Also, if you go with the otos give them a tiny plastic plant or something to give them cover, as they are shy and basically nocturnal, and like a hidey hole. I rarely if ever see mine in the 55-gal!