A few months ago I spotted a few flatworms and freaked out. I was also battling zoo eating nudibranches a the time
Anyway, I have not seen any flatworms or nudis since I got a flame angel a couple of months ago! I almost returned him because he was picking at all my corals! I later discovered that he actually wasn't bothering any of the corals, he was just hunting for food and was eating something else. He still pecks at them but I have not seen any damage to any of my colonies or frags.