Orange shoulder and questions

[jomatty]

My orange shoulder tang has a black mark on its right front side. Does anyone know what this is. And how much cause for concern it is. I can set up a hospital tank and have sponges in the sump for filtration but do not know how I would get the fish out of the tank without completely dismantling the tank. The fish is eating nori very well and also lysis when I feed the other fish. How worried should I be and is there anything I can do? The only new addition to the tank is a rose bubble tip But I can't imagine it could sting a tang enough to make a visible mark but perhaps I am wrong. Any information is very much appreciated

 

[jedidad]

the picture is too small to really tell but i know when i added a rbta to my tank for my clown they developed small black spots from the sting from it until they got used to it. they looked like the spots from ich but black instead of white. the rbta could be the culprit. if it is otherwise acting normal and healthy i would just keep an eye on it.

 

[jomatty]

Thank you very much. I've spent an hour trying to get a better picture and he is just not cooperating. If I can get a better one I will post it thanks

 

[jomatty]

Is this picture any better?
I am having trouble sizing it (computer dummy)

 

[jomatty]

Can anyone tell what that is behind it's gills on the lower half of its body?