A GUIDE TO TREATMENT - SNAILS
Although they can build up to large numbers in an aquarium or pond, and on occasion act as a source of certain parasite infestations, snails cannot really be regarded as a major threat to the health of ornamental fish. They will often eat fish eggs however.
While a number of different chemicals can be used to combat snails in an aquarium or pond, such treatments must be nontoxic to fish and plants. A number of proprietary snail treatments are available, which are effective and safe to use. However, be sure to follow the manufacturer's instructions closely, and only use them as a last resort.
Although mainly considered a pest, common snails are quite effective at controlling algae and breaking down waste such as excess food, which may have gathered on your gravel, around filters and in hard-to-clean places. It's often the volume of pest snails which causes the problem, they are capable of reproducing in massive numbers and will also produce their own waste. They are rather parcial to eating expensive aquarium plants. Most snails will be brought in on aquarium plants, often without knowledge of the unsuspecting fishkeeper.
By far the most popular and effective treatment on the market is eSHa Gastropex, a treatment of choice for fish keepers for many years. Its well tolerated by fish and plants, clears cloudy water (bacterial blooms) and combats Hydra. A treatment course can be applied in-situ to clear infestations of snails, and can also be used as a preventative bath for new plants.
To minimise the risk of introducing snails when buying new plants for your aquarium, choosing a range that is guaranteed snail-free is often a good idea. The Tropica In-Vitro range is a good example of such.
Lots of fish eat snails - loaches, some catfish, cichlids. Convict cichlid's are particularly good predators, as are Koi and large goldfish. Puffers are the most adapted to eat snails, and will often be fed them by their keepers. You can also try to introduce Assassins snails, who will (slowly!) prey on all types of snail, but then you are introducing another type of snail to your aquarium, which may negate the original purpose.
Water quality problems can suddenly develop in aquariums harbouring large numbers of snails that die following the use of a snail eradicator. Use with care under such circumstances, and remove all dead snails promptly. Some snails, such as the Malayan livebearing snail (Melanoids), may abound, hidden in gravel. Its often a good idea to remove as many snails by hand before administering a treatment, to minimise the risk of this happening.