I agree with the snails...if you put in a snail be careful of which species you chose bc some are asexual and can produce their own babies by the hundreds in no time at all. They leave a slime layer and you may end up with tons of babies everywhere. They also can damage your plants. I am not familiar with snail species names, but the small blackish brown ones are a nuisance.

The ones who do not reproduce on their own may be ok?