I would advise against adding snails to a pond. Snails are an intermediate host for several fish parasites. If you eliminate the snail population in a pond you eliminate the life cycle of such parasites. I personally would never add snails to a pond. If you are that concerned about algae, rake it out, it would be more effective.
please dont add snails, they will most likely show up in your pond all on their own, but make them work for it. have you thought about fresh water shrimp?? There is interesting info on the site about them.
