Otocinclus Catfish do a good job on eating algae and don't get very big and are very peaceful. I agree with Prince Powder about the bettas though. I've heard of several cases of them getting nasty with guppies apparently because they have the pretty long fins like bettas too. That said I have heard about people keeping them together without problems. I'd be careful with a lot of algae eaters though because some of them get huge. I'm thinking about getting a couple of otos too
EDIT: I forgot to say, you can only really add the otos to quite established tanks I believe so you might want to wait a while if you only set it up in January
