dead damsel, white stuff around mouth

[bobothefish]

I had a bi color damsel died last night. had it for 4 days. noticed white stuff around mouth looked like dead skin could see teeth as if skin was eaten away. only thing I put in tank was coroline stimulator. I got a 55 gallon with sailfin tang, very colorful wrasse, chromie, yellow tail damsel and a clown. 80 lbs of live rock,80 live sand cuc. I know I brought it from the pet store sick because I noticed it upon arrival. acclamated w/ a drip line ina clean bucket just like the others. Ate fine I think, tank parametes are great 0a, 0n, ph 8.0,nitrate 10. Fish was acting ok in my op.
I just dont want my others to get sick here is a pic.
What is it and how do I treat the tank in case of poosble contanimation?

 

[melosu58]

I really dont know what it could be. It could even be from aggression issues with other fish. When you say white stuff are you talking something slimey or like tufts or like little heads of cauliflower. I`m thinking maybe something fungal but not sure.

 

[match55]

sorry can't help in here, but really sorry for your lost. >O<