Brief info on breeding them.
Stomatella snails are easy to breed and will spawn spontaneously if they are kept in a well established marine tank. All Stomatella snails of the same species will spawn at the same time. They usually spawn during the day when they crawl to a high point in the aquarium. They then release egg and milt directly into the water were fertilization takes place. You can sometime see how the water suddenly becomes cloudy in a tank containing Stomatella snails as a result of their spawning. This is nothing to worry about and will clear up relatively quickly. Some fish and filter feeders will eat the milt and eggs. Stomatella snails only very seldom multiply enough to become a nuisance. Established populations can be taxed hard without a lasting impact on the population if you want to sell some of your excess snails.
I would try to sell some back to your lfs