yellow tang sick???

[kui loach]

Please help me. My yellow tang has spots or abscence of color
onit on its top and lower fin. Could it be from it bumping into
therock and getting its fins damaged. It is not ick is it? It
iseating fine. I also have a perc and goby along with a
hermitcrab, snails, and many(at least 10 bristle worms of
varioussizes.) Also are that many bristle worms OK? My ph is 8.2,
sp gr1.023,nitrate 12.5, kh 10. I did a water change on 12-22 of
9gallons. Anything that I can do for the yellow tang? Also
Iuse an ecosystem miracle mud filter. On my live rock, there
isalso all this gray junk that resembles vacuum cleaner dust. It
isespecially noted on the rock at the back of the tank What is
thatstuff? When I did the water change I could not get rid
ofit. Thanks

[mutts]

This is what it sounds like:


Thats a pic I stole from live aquaria. Spots like that are normal from what I have seen and read. But if you can post a pic of your tang up on line so we can all see. We might be able to help more then!