Naso Tang grey spot/white erosion

[bch grl]

Please help a newbie!
Got a Naso Tang 5 days ago, no QT(I know) and put him in our 75 gallon tank with a yellow tang, 3-stripe grouper, and snowflake eelHow havebeen in the tank for more than a year. He developed a grey patch of both sides beneath his pec fins. Next day the patches turned white and it SEEMS as if his fins are scraping off his flesh. However, the grey area has enlarged beyond his fin size. Can anyone help me? Beth, it is OK to post the pics. And I just found this site so I'm searching as fast as I can! Thanks for any help!

 

[elfdoctors]

Nice picture!
My first thought is aggression. Have the yellow tang and your naso been fighting?
How are your readings?
That is a small tank for a fish which can get to 18 inches!
Welcome to the Boards!

 

[bch grl]

Thank you for the comments...didn't realize that it would get that big!
The sad news is it died the day after the post. The good news is that I have learned a great deal from this and other websites and won't make the size mistake again!
It didn't start as aggression, only after white eroded area was there for several days did the other fish start bothering the tang, and then it was the small yellow tang. We isolated the sick tang in part of the tank after the picking started.
The water readings were no nitrites, pH=8.2, temp=78, ammonia was at the lowest reading(I forget the number). We had been working on getting the numbers as good as possible, we had lost a new fish a few months ago and didn't want to make the same mistake!
Thanks for your help and the boards!