Don't blame the fish, the shop should have advised you that they are not reef safe, if they didn't take it back!!
In saying that I have got a beauty have had it for 2 years I also have a Bi colour. They only pick bad if I don't feed enough, I have tried to cut my feeding back to once a day but they start to pick bad. Also I put in a vegi clip if they pick that keeps them happy. There is only two corals I have had to put in the small tank because they think they are a salad bar.
Having said all that I love my Lemon Peel and wouldn't get rid of it!!