I have noticed something similar to barnacles on my Yellow tang's fins. Everything in tank is fine except for that. Tang seems happy and eats regularly. I am curious about the barnacles. Any clues?
Any chance of getting a pic?
Can you give us more info about your tank? Are your readings okay? Is anything in your tank new? Does the fish seem bothered by the growths (e.g. scratching at rocks)?
The most likely explanation is some sort of parasitic disease (including ich in that group). Are you sure that the rest of the fish is normal? Ich can be very difficult to spot on the body of this light colored fish.
Tank is asleep for the night but I will try to get pic tomorrow. Does not look like ich. I have had that before and this is different. It looks like a barnacle on the tip of his anal fin and I just noticed a smaller one on his dorsal fin. He shows no signs of distress such as rubbing or any other erratic behavior. Everything else in the tank is stable and all of my readings are excellent.