Powder Blue disease/gash? please help!

[jamesjre]

came home from work today and found my powder blue tang with a horrible gash on 1 of its sides, its like the top layer of skin has come off, have had the fish for almost a year with no problems, he is still eating, but not moving very fast at all, or moving very comfortably. am very concerned as to what it is, and if at all it is treatable? all other fish are fine in tank with no marks what so ever on them.
if some one could shed some light on what this is, would be appreciated. thanks

 

[Ostara]

Do you have a heater in the display? It looks like wounds I've seen caused by fish leaning on or brushing up against heaters when they're on.

Regardless of what caused it, I don't think I'd risk the usual "maintain great water quality and see if it heals" approach. I'd get the fish into a quarantine for observation and have antibiotics on hand. Powder blues are sensitive and that is such a large, nasty wound that I would suspect the chances of him getting an infection are fairly high.

 

[jamesjre]

Na I don't have a heater in the display tank. It's in the sump at the bottom, do you think it has caught against the live rock in the tank? Checked water levels, all are ok, he was the first fish out swimming when I put the tank light on this morning, but his hash didn't look any better, I haven't got a QT so I'm pretty buggered there, il keep a close eye on him and hopes he heals