Ramshorn snails (Planorbidae) is a kind of aquarium algae eater which feed on most types of Algae, as well as any dieing or decaying waste in the tank. As an algae snails, they will not eat live plants or damage live plants; however they do make very short order of any wilting leaves in a tank.
The aquarium experts found that ramshorn will even remove Cyanobacteria (Blue green algae) from a tank. The effect is not only one of regulating the organics that may contribute to Cyanobacteria, but the snails attack and eat the bio-film which makes up the base of blue green algae.
A few of these algae snails can strip a pretty large plant of all algae or Cyaonobacteria overnight. Red Ramshorn snail are also said to eat Hydra. They are considered to be the best available cure for aquarium hydra on the market. Better to have not personally tried them for this particular issue, but given their other merits and their seemingly unconditional appetite for anything nasty in a tank, no doubts they would be worth a try if you had an issue with hydra.
Aside from food Ramshorn snails have very few requirements. They do breathe air, and need to travel to the top on occasion, but from some resources it is not often that they need to do so. They have a very large pulmonary chamber inside the shell which allows them to store a lot of air. They are a true aquatic snails but do not have gills.
To control snails population in your aquarium you may should keep reading on these below. If there is abundant food and calcium to promote growth, then the Ramshorn snails like most scavengers will reproduce at a rate relative to the available food in a tank. If you have a lot of waste and a lot of Algae, then you will have a lot of snails. However, if you limit waste, feeding your aquarium fish conservatively and do not promote algae growth, then the population of Ramshorn snails and other algae snails will remain smaller.
If the Ramshorn snail population explodes, first you need to clean the tank for the snail control and then you can reduce the population by removing the smaller snails while leaving the largest ones in order to keep control the algae growth in aquariums. Since the larger Ramshorn snails eat more, there will be less available food per snail and less of a tendency to reproduce as long as the tank stays clean.