Another tang problem. Help ID this.

[125mph]

So that same purple tang that has some strange markings on him a few weeks ago. We suspected it was lymph but that went away after I turned skimmer back on.. but has appeared clean for the last few days. 2 hours ago I was looking at him and he appeared healthy with no markings.That was two hours ago..

Now he looks like this: what could this be? Looks like his fin is damaged some how..

 

[TheAngelfish]

Aggression from other tankmates maybe?

 

[125mph]

Strange.. he looks almost normal again today.. only slight color change at the tips of the fins...

I dont think its tank mates. Havent seen any harassing.