I had a clown that had the same thing growing on it's face and sides. They grew larger and larger but eventually went away on it's own. I did a FW dip twice thinking it was a parasite or some fungus. The FW dip did not seem to help. The behavior of the clown never changed and it continued to eat so I did not worry too much. I would just give it some time. Do you have a cleaner shrimp? Maybe they would clean it off?
I first noticed it about a month ago. I let it go for about a week before posting anything. It has gotten progressively worse. Her behavior has been normal, she just looks terrible. I do have a cleaner shrimp, but the only thing I have ever seen him clean is my hand at feeding time lol.