Actually, when I bought my guppies, and asked for and got some new snails, the guy in the aquarium shop told me that snails are very good to have in the aquarium, since they do a lot of good. They eat stuff, like the brown plant leaves that otherwise might start to rot, and left-over food, and the like. So they improve water qualite in the aquarium! I actually did not know that, but of course it is a good thing!
He actually said that all snails are good, even Physa marmorata that is often considered a pest... I asked him especially about that since some snails have a better reputation than other snails...
Physa marmorata
The snail in the two photos here is 6 mm long, but I have bigger ones of the same kind. In the photo to the left you can see it from the side and in the photo to the right you can see the same snail from behind. When I got them I was told they were Ampullaria baby snails. They grow very fast and they do lay their eggs above water. This is the kind of snail that came with all the plants I bought at the aquarium shop, and there's a lot of them. I hav ...