I don't QT them BUT they can carry parasites soooo you have to decide if it's worth the risk. Many years ago I made a big mistake of adding several Japanese Trapdoor Snails to one of my smaller pond and they were carrying flukes... that was not fun. But overall today most people just add snails straight into their tanks. Heck alot of times you accidently add hitch hiker snails to your tank without even knowing. So you need to decide what your most comfortable doing.