[pogodzib]

There are not many parasites that would affect fish like that without being able to be seen on the fish's scales. Take a close look to see if you can see anything. Internal issues usually take a while to develop so you can probably rule that out. If you can't see anything on the fish, my best guess would be that you had something happen to your water quality. I'd make sure that your water is getting plenty of oxygen by increasing surface agitation and making sure your skimmer is sucking in plenty of air. Also, adding an airstone into the tank for a little while may be beneficial, if you can find a place for it that won't impact your corals directly. The next thing I would do would be a 25% water change and then wait and see how your fish respond.