Aquarium invertebrates
In fresh waters there are some bivalves called fresh water shells. Even if they differ from the salt water shells, they are relatives with salt water shells. Fresh water shells stay totally or partial stuck into the ground. In order to feed, they filtrate the micro plants from the water. This kind of eating can be useful in an aquarium because it may stop the overflow of algae. Instead, if the feeding is wrong, they can die and that`s a risk of pollution because you can`t observe that immediately. You can rarely see this kind of bivalves in our freshwater aquariums, because tropical bivalves are very rare on the market.
Some Gastropods species are considered embarrassing, the physes for example, while others are considered like having an important use in cleaning the aquarium from the undesirable algae. In this last category we include aquarium snails, ampullaria species, Malay snails and others. In good conditions they proliferate a lot and can be removed by hand or with a trap; if you introduce a boiled salad leaf or a spinach one in the aquarium during night, the next morning the leaf will be covered by the aquarium snails and you`ll be able to remove them from the aquarium. The sudden death of a gastropods population is a sign that the aquarium equilibrium has been broken.
Ampullaria sp.
are a category of aquarium snails that can grow very big, reaching the size of the terrestrial snails. They are very good cleaners because they eat the excess of food rests, but if that food isn`t enough they`ll start eating the aquarium plants. They build a nest with eggs outside the aquarium water, usually on the interior face of the aquarium, and the baby snails will fall into water after they hatch. They have an auxiliary respiration system, which they use to breathe atmospheric air when the quality of the aquarium water is not good enough. When they feel the danger, they hide in their shell and close it with a lid. It`s not hard to control the population of ampullaria aquarium snails because they have big size.
Helisoma nigricans 
is a specie of aquarium snails native from Brazil. They have almost a perfect circular shape and their diameter hardly reaches 1.8 cm. They are red-brown colored and they are very sensitive to temperature. If the temperature decreases below 20° C they die. A similar specie is Planorbis corneus. It lives in Europe and it`s completely harmless, though it won`t survive with a pH higher than 7.
Melanoides tuberculata is the most common aquarium snail. It can be found from Egypt to India and needs a temperature
of at least 20° C. It can`t survive without minerals because it needs them in order to build its shell. It feeds with algae and food rests from aquarium fish; that`s why it is considered a great aquarium cleaner. It is a nocturne aquarium snail, during day time it hides in the ground of the aquarium. We`ll never be able to know how many aquarium snails like this we have, only if we turn off the light and return it on after 2-3 hours. In short time they propagate a lot and they give the impression of a moving ground because their movement. This is a great advantage for aquarium plants because the snails aerate the roots of the plants. Their only disadvantage is that they get into everything (even into the filter). Sometimes you can see lots of Melanoides tuberculata snails at the surface of the aquarium water; that`s a sign of water pollution