Help with yellow tang

[Akakta]

Ok so I have a 150 gallon tank it's been up and running for about ten years. Taking it over for a friend. It has a wet/dry filter, live rock, hermits, sponges, a little mandarin, tube worms, etc. i only have two fish in it. The little mandarin and just added a yellow tang. The yellow was added two days ago and now has little black spots on it. What are they and is this bad?

 

[Tahoe61]

Black Ich: Please review the link below. There is a lot of mis-information and bad advice so do your research carefully.

Yellow Tang Black Ich Scopas Tang - Reef Central Online Community