Please help identify what this is

[TEC]

Bought a yellow tang. Was fine for two days then developed a growth on its back end. Been unable to find anything online to identify what this is. Have it in QT which has coppersafe treatment in it. Any ideas as to what it is and how to treat it.

 

[Mr. E Wrasse]

Welcom to r2r! And that is odd... is it growing fast or did it just appear one day?

 

[TEC]

It grew overnight and has remained the same size for about three week.

 

[Jon Schutte]

Any other tangs in the same tank. With it so close to his barb maybe he got in a fight.

 

[TEC]

Nope, he was the only tang in the tank I had two small clowns in with it and they showed no signs of the growth.