There are snails. And then there are snails! They can be a disaster or a bonus, depending on the type of fish you’re keeping, and the type of tank.
In spawning tanks, snails can cause havoc by eating the eggs. In fry tanks they can perform a valuable housekeeping service, although period thinning may be required to prevent them taking over.
The Malaysian Trumpet Snail is a tiny (2 cm) nocturnal species with a perfect cone-shaped shell that lives in the substrate. This species can be beneficial in most tanks as it keeps the gravel loose and free of debris.
Ramshorn Snails are common. They come in various sizes, with the striped Columbian Ramshorn reaching 2 inches. These snails are highly prolific, and have a fondness for plants, although they’re not averse to enjoying fish spawn.
Pond Snails are football shaped and under 2 cm in length. They are easily introduced into a tank on new plants, although they are usually to be avoided, as they can introduce pests. They also happily eat plants.
Mystery Snails have spiral shaped shells similar in shape to those of pond snails, but they grow consid-erably larger, and come in a variety of colors. These snails generally prefer dead matter to plants.
— G.C.K.A. Newsletter, October 1996