Japanese Trapdoor Snails (pond snails, (Viviparous Malleatus) are algae eaters, feeding on the hairy algae that often grows in spring and summer. Japanese Trapdoor Snails produce 20-25 young in their lifetime, and do so over a number of years. Typically, you should see one snail per every 10 gallons of water in a small, ornamental pond. One snail per every 20-25 gallons per 1500-8000 gallons. On larger ponds or lakes, the number is even fewer. Overall, pond snails are less expensive than weekly algaecide.Pond snails, if used in the right numbers, is a great defense against bottom sludge and hair algae.
Make sure you are near the pond when you open your bag of snails. They will come bagged with air and oxygen to survive the trip. Gently add a cup or two of water from your pond to acclimate your snails to your pond water. Gently pour the snails into your pond from the bag.The snails will have their trapdoors closed so they will sink to the bottom of the pond. They may sit there for a while until they become acclimated, then they will begin the task of cleaning sludge from the bottom of the pond and begin to eat algae as well. You will rarely see them as they will stay on the bottom or on the stems and leaves of plants beneath the surface of the water.