Prevention is better than cure, as they say. The occurrence of snails as such can sometimes not be prevented, and in some ways, even desirable. Avoid overfeeding your pet fish, for excess food will be consumed by snails. Healthy snails will multiply rapidly, causing an infestation. Overhaul your fish tank and clean everything, even the gravel, rock, and sand. In small numbers, snails are beneficial to the fish tank.