What kind of fresh water fish cleans the gravel in the bottom of a 12 gallon tank?

I have a 12 gallon tank with 2 small plastic plants and a cave looking little house thing. we have 2 Otto Algae eaters, 2 baby panda catfish, and a neon tetra and one of those rasbora things with the black triangle on their sides. We had 2 cory catfish 2 neons 2 gold tetras 2 of the rasboras 2 zebra danios and 3 rummy noses and they were all fine until they got this bacteria thing and it killed all but 2 fish, the rasbora and the neon. then we got the ottos and the pandas because we thought the problem was to much food build up. they won't clean the bottom of the tank and theres starting to get a bunch food and we don't want the same thing to happen. today we were going to get 2 more neons and another rasbora and were thinking about getting 2 ghost shrimp. tell me if we should et ghost shrimp or some other kind of fish that they would sell at Petsmart that doesnt get over 3 inches big. THANKS!