Snails are not that big a deal. Take a breather... Stock 50-100 3"+ RES and if they are your normal pond snails, between them, YP and CC their numbers will drop fast. Snails could have come into your pond in one of many ways. They are far more likely to hitchhike on a bird than say eggs of a fish and live. If you bucket stocked or even from a hatchery, they could have come in that way as well. Snails sometimes just find their way. I wouldn't stress out over them. I like having snails in my pond. I introduced a few different species to increase the food chain.
