have you thought of addressing the cause. Snails are great things to have in a tank (yes even pond snails) they are like a feed-o-meter. The only really bad thing about snails is that some of them eat plants. try reducing the amount and the frequency of your feedings. I promise they will reduce in numbers within a month probably less. I feed once a day, but I think you should feed once every other day until the snail pop. gets under control. Seriously don't touch the meds, There is no reason to. Just reduce feeding and that'll take care of it. It won't get rid of all the snails but it will reduce the pop. to something more manageable.