Duncan brown slim over it

My Duncan has split off like five heads. I moved him and he jumped off the rock and tried to take his own life Lol.
I caught it quick but the original head now has brown slim over it. Now the outside heads are starting to get some more color. Is this normal? Everything is at the right levels in the tank.

 

Remove that coral and dip it as soon as you can. First put it in a small bowl of tank water and swirl it around to removing any dead or dying tissue/decay. Next dip in an Iodine based solution/diluted if you have that, if not coral RX or Revive. You may have to repeat process.

 

Agreed. Blowing the damaged area of the skeleton off with a turkey baster from time to time may help as well.