Just so you have both sides of the story...I would not recommend any "treatment" for snails. Java Moss is a delicate plant that likely will react to any substance like excessive copper or bleach. Most will tell you never to use copper-based medications in a planted aquarium for good reason. Additionally, most snails lay eggs, and these would not be killed unless the copper/bleach was so powerful that it would seriously damage the plant if not kill it as well.
Snails are not a problem, though I understand many have a dislike to them for some reason. But the sort of snails that are likely to arrive with plants are the small species that are very beneficial in your aquarium, your "best friend" in fact, and worth having.