Black Japanese Snails are scavengers for the water garden because they scour the bottom and sides looking for decomposing organic debris and algae. The recommended stocking rate is one snail per every 1-2 square feet of pond surface, or one snail for every 10-20 gallons. Many people will say that it sounds like a lot of snails to put in. But consider how small their mouth is and how much territory they have to graze. It takes quite a few snails to make a difference. This rate still allows plenty of room for growth and reproduction. We suggest that you stock your pond with snails at the same time you install the plants allowing the pond to begin establishing its own natural bacteria. Once organic debris begins to be formed, the snails will start to feed on it.
Black Japanese Snails are live-bearing creatures, meaning they are not egg layers. Other snails that lay eggs tend to over-populate a pond very quickly. A live-bearing snail may produce 5-10 snails at a time, not likely to cause a population explosion.