What disease my yellow tang has?

[Damorx]

I saw it last night , it disappeared this morning and now it's back.
What is the name of the disease and what i can so about it?
Thanks in advance

 

[Damorx]

https://flic.kr/p/UW5YTb
https://flic.kr/p/UezUTu
https://flic.kr/p/UhCYuT

 

[Damorx]

Ok just tead somewhere it might be because the lights are off
The yellow tangs change color at night !?!

 

[jerrypam5855]

Every yellow tang I have had change a little dark after lights out.The color comes back after the lights are on for a while.No problems with your tang.

 

[Damorx]

Just an Update my yellow tang is fine- The black spot was because of the light
It does go back to yellow when i turn on the light

 

[jerrypam5855]

Tang

Tang

That's good. I have one in QT now and it does the same thing.Like I said everyone I have had doe's this.I have had several over the last 40 years