New Black Velvet Angel

[NexDog]

If the snail is in a tank with fish with visible Ich infection, then no point in tempting fate. Just get some snails from somewhere else.

 

[LukFox]

You could also just leave any non-fish (snails, coral, etc) in a fishless QT for 8-12 weeks. No treatment necessary, as the parasites cannot survive without a host. I go through all the trouble of QTing fish, so I think I'd be pretty upset if something like a snail ruined everything no matter how slim the odds.