Brook just appearing?

[ylee0710]

I have had a pair of true percs for over a month now(have not added anything to the tank for awhile) and on my female i am seeing what looks like a white film on her dark parts near her dorsal fin. Not a lot but still there. Every now and then she will rub up against a rock and swim away, then go back swipe the rock again and swim away. any ideas of whats up?....thanks