I've never seen a clown that had an anemone have ich. I think once they 'slime-up' for residence in a nem, it protects from ich as well. I have, however, seen plenty of clowns with ich. Part of their problem is they're often the first fish, with a new hobbyist, in an unstable tank---and that is a status that can cause stress. That's one reason I advise waiting. There are fish that are less susceptible. And the clowns are definitely happier if they have something nem-like to live in. So I maintain if you want one, wait until your tank can support a nem and then bring in a healthy (qt'd!!!) clown pair, and you'll have a happy experience (until the lil beggar decides to defend!)