50 lot of Cerith snails. Great for diatom blooms! Cerith snails are among the most versatile and valuable members of the clean-up crew. We think every tank should have them! They are excellent at eating diatom algae (rust-colored film) and even do some borrowing in the substrate, keeping things stirred up. It's hard to have too many of these guys. We've seen some great tanks that had as many as one per gallon, but even concentrations as low as one per five gallons will help.