Some aquarists view snails as invaluable algae eaters and scavengers who help keep tanks clean and in balance; to others they're loathed pests that quickly take over their tanks and are hard to rid themselves of.
Snails often sneak their way into aquariums through hitchhiking on live plants, rocks, driftwood or decorations - or from used gravel bags meant to jumpstart their biological cycle - or by hiding in bags of used gravel intended to start an aquarium's biological cycle. Once inside an aquarium, snails reproduce quickly and can overpopulate tanks when left unchecked - leading some people to consider them nuisance snails; these snails are known as bad or nuisance snails and seen as signs that proper aquarium care hasn't been taken - especially prolific freshwater species such as ramshorn and Malaysian trumpet snails are notoriously hard to eliminate from aquariums!
Nerite snails (Melanodes tuberculata) can also pose problems in aquariums. These nocturnal creatures with pointy elongated shells reminiscent of ram's horns live mostly subterranean lives before emerging at night foraging and foraging for food scavenger. As an added benefit they aerate the gravel while helping scavenge for unwanted debris while at the same time acting as natural air filters for brackish aquariums while hermaphrodites they will spawn their eggs at will, leading to massive population explosions in brackish environments.
Nerite snails have also been known to contribute to water quality issues by excreting large amounts of waste, which can overwhelm biofilters and cloud up an aquarium, as well as clog filters and inlet filters. To minimize these problems, only add them into saltwater tanks specifically designed to accommodate them.