Talbot Damsel - white mouth

[Gremlin]

My Talbot has been keeping to himself for a couple of days & not eating. Today, he seems to have 'swollen' white lips. Cant get a great pic, but have 2. [How do I attach pics to message?]

Normally eats pellets & frozen. Now, swims up to the pellets, but then turns away.

150g tank started in Feb. Last addition is a blue tang about 4 weeks ago. Everyone else seems happy/active.

Ideas of what it is? Treatable? Other fish in danger?

Thanks in advance.
David

[CMD2213]

Have any other fish that he may be locking jaws with for dominance?

[Gremlin]

Not that I have seen. Never seen anyone go head-to-head. Pretty peaceful tank.