Beth is right, use a quarantine, I can't stress that enough... If you want a parasite prevention in the tank...a just in case, you missed something kind of thing...get a couple of skunk cleaner shrimp, they like to feed on parasites on the fish.
They will set up a little cleaning station, and the fish will actually go there to be "cleaned up". They will not, and can not replace a quarantine, because new fish are super stressed, and the parasite would multiply in such numbers it can kill off an entire tank of fish....it would just be too much for a couple of cleaner shrimp to handle. They only pick off what they want to eat, and once they are fed, they stop...a tank full of sick parasite loaded fish would be doomed.