FWIW, apple snails and mystery snails are the exact same animal. there is only one kind that gets really huge, and it isn't all too common in the aquarium trade, really. most of the commmon ones at the store won't get bigger than 2".TKOS said:I would say an apple snail is too much for that tank as well. They can get huge. A Mystery Snail would be best as they don't get as huge and are great cleaners. If you are looking for bottom feeders to clean the tank then just so you know cories don't eat waste, few fish do. Snails will pick through it though and are cool to watch.
apple snails in general are good cleaners, but they don't really eat algae. I have a columbian ramshorn and he eats rotten plantstuffs, algae wafers, fish flakes, and anything else that makes it to the bottom. some are voracious eaters of live plants, though, so be careful if you want live plants. my RH never touches my live plants, only dead ones, but I know many of them will eat live plants.