Aquarium snails are any kind of snail that can be kept in an aquarium setting, whether that be freshwater, saltwater or brackish. Most people purchase these snails not only for their appealing looks, but also because they help with the upkeep of the tank. Some of the most popular freshwater snails are apple, mystery, and nerite snails which all help with algae and detritus. Assassin snails are also popular with eliminating pest snails in your tank.