Is it a good idea to add snails to my aquarium?
Snails do add interest to an aquarium, and some, such as the yellow form of the apple snail are very attractive. But bear in mind these molluscs can reproduce very quickly under good conditions, and may soon reach plague proportions. Their appetite is likely to cause them to turn their attentions to aquarium plants, which may already have to cope with the attention of some of the fish as well.
This photograph gives an indication of how many young snails can be produced from a single spawning. Since the snails are hermaphrodite, with both sexes present in their bodies, so even if you have only two snails, they will both be laying fertile eggs.

Should you find that the tank is being over-run with snails, you can trap them quite easily using an inverted clean saucer, by placing fish food tablets on the base at night. The snails will be attracted here to feed, and can be lifted out on the saucer in the morning. If your aquarium contains freshwater pufferfish however, then it will probably be impossible to keep even a small number of snails alongside these fish, as they are likely to eat them.