Please help my Clown.

[MstgKillr]

I will post pictures as soon as I can.

Last night I noticed my female Picasso Clown is missing her tail, most of her left fin, and parts of her side looks scratched and discolored. She is having a hard time swimming and has stopped eating. All of this has happened over night or maybe in the last day or two. I really don't know for sure as I have been focusing on my Naso that stopped eating for a few days. The Naso is fat and back to normal now for whatever reason but it looks like my clown is going to die.

Any opinions of what could have caused her to lose her fins so fast, maybe tail rot or another fish nipping her fins. BTW my water quality is great so that can be ruled out.

I have a 215 gallon SPS tank with the following fish that never show any aggression and get along fine.
Naso Tang
Purple Tang
Sailfin Tang
Foxface
Yellow Watchman Goby
Small 5 Line Mystery Wrasse
Mandarin Goby
Pair of Picasso Clowns
Lawnmower Blenny

Please help I don't know what to do and I really don't want to lose this fish.

 

[fish2009]

I recently found a Sally Lightfoot crab that must have hijacked its way in when I added some new live rock. The interesting thing for me was that I had not added any new rock for several months. Ended up having to catch the crab and move it to another tank

 

[guy145]

hey mstgkillr just wondering you got all those fish did your fish ever have ich did you get rid of it or is it always around?