Unknown disease

[zrostratum]

I have a 8" Z.rostratum Tang in a peaceful understocked 125g community tank. Eats like a pig (Varied diet i.e.Red seaweed, mysis, angel diet,etc.Have had it in a healthy tank for 4 months. All parameters OK. Fat and no HLLE. The "disease" looks like EXACTLY like a green bubble algae patch about 1.5" by 1/2" on one side in front of scalpel. It literally happened overnight, and has been there 2 days. Very strange.I have had marine fish for 40 years and I am stumped. First I thought it was a wound, but it has no blood or missing/ripped skin/fungus. Looks very clean almost as if it was glued on like a fake mustache. I tried to take a pic of it but since the fish is black and the patch is dark green, you really can't see very much. The bubbles are raised maybe 1/10th of an inch off the fish. The fish doesn't seem to be bothered by this at all yet. At this stage,I don't want to stress the fish out to catch it and use a topical (antibiotic?) Tang's skin is abrasive and thick so maybe it is just some flotsam from the tank?:uhoh3:
Any serious help would be appreciated. Thanks

 

[Deinonych]

Can you post a picture?

 

[snorvich]

I have never seen this issue. Is there an anemone in the tank?

 

[zrostratum]

I'll try to post a pic. No anemones just mushrooms and a few hammer frags. Lg montipora and a med.galaxy coral. Thanks:headwally:

 

[zrostratum]

I guess I'm not sure how to post a pic on the forum.I have pics in my album:sad1:

 

[zrostratum]

This is the best pic I could get area in question is dark green in person

 

[zrostratum]

Fell off in 3 days.Everyone healthy.Most likely chunk of algae from back of tank. Not lymph, but my girlfriend got an image of a Z.scopas with a similar patch in the same area under lymph images on Bing.Thanks:love2::thumbsup: