Help!!

[Gmoney001]

Hi everyone, new to this site and still a relative novice to the hobby.
Recently introduced this clown to already established tank and this happens!
Anyone have any ideas as to how to help him?
Picture is from two days ago, and brown growth seems to have settle but now appears as tho there is a giant hole in the bottom on his jaw....

 

[Newsmyrna80]

Try an antibiotic in a hospital tank.