Pond snails are one of our better choices for out-door aquarium cleaners such as in ponds.
They are ideal for shallow and smaller tanks, since they need to come to the surface of the tank to breath, but will not usually climb out of the tank.
They can survive temperatures as low as 15C up to 30C but thrive between 20 and 26 Degrees, and getting at least 5 will soon net you a collony of them to keep your tank fresh.
If you keep your tank in-doors or heated, we preffer Rams Horns due to them being quite a bit larger, but these do fine as well.
Thanks!