Do snails have to be in QT just like fish, I bought 4 tonight to help control some algea in my native tanks, I have the snails in QT for now but not sure if snails can carry infections that can be passed on.
Good thought. I have never put mine in QT and knock on wood, never had any problems. I suppose it wouldn't hurt to do so though. Try googling your question maybe?
It certainly won't hurt to have them in quarantine for a week or two. There are a few parasites that have a stage that need snails, but, as far as I know, they're not common parasites and probably not on tank-bred mystery snails.
They don't actually get fish diseases, but they can carry things like parasites and ick and can pass them onto your fish. It's pretty rare to have this happen. They are sensitive to medications and obviously sensitive to salt, so I don't know how you would ever treat them for anything they may have. I have never heard of anyone in my personal experience having any trouble with adding them to the tank.