Planted Tank Guru
Join Date: Jan 2010
Location: Contra Costa CA
The largest pond snail I have seen was about 1/2" diameter. Most are smaller, between 1/4" and 1/2". I would not be surprised if they got a bit larger, but not much.
Snails live on the fallen food the fish are not eating, or algae, or other things.
The algae and other things can be minimized, and the fallen food can be reduced to almost nothing. Taking these measures will reduce the reproduction of the snails so you pretty much only find the adults with almost no babies.
Some fish eat snails. If you like these fish, and the tank is well suited to them you might think about getting some.
Most Loaches such as Yoyos, Clowns and Kubotai eat snails. They are social, and grow too large for smaller tanks. Yoyos are more aggressive, and are active predators, too. They can eat fish the size of Neon Tetras. Many Loaches dig, and Yoyos are large enough and willing to dig up plants. Clowns and Kubotai seem not so interested in digging, though they are certainly large enough to do serious damage to a planted tank.
Kuhlie Loaches might help a bit. They have small mouths and cannot eat a snail that has hardened its shell, but baby snails with really thin shells can be eaten. Kuhlies also are social fish, but a quite compatible with most of the small fish we often keep in planted tanks. They dig, but are so small they are more likely helping by opening channels for the water to enter the substrate.
Loaches like Hillstreams are not snail predators.
Many Cichlids will eat snails.
Some other fish can be trained to eat them. Squish a snail against the glass and let the fish eat it. Some fish figure out how to eat snails, once they know there is food.