Fish is displaying a behavior associated with Flukes which they are susceptible to. Known as flashing, other signs will be rapid breathing, fish acting lethargic or swimming near the water surface, hiding in the corner of tank or behind rocks, loss of appetite, shaking its head, flashing/darting, develop clamped fins, , or scratching against objects. They may also exhibit what looks like yawning from gill irritation develop, cloudy eyes and loss of color .
You can also try a 5 minute freshwater dip in water the same temperature as display tank and return fish to display tank. This not only offers temporary relief but you can then check the bottom of that container for what looks like sesame seeds or fish scales. If you see that - Flukes it is.
Treatment of choice is PraziPro and while reef safe I prefer QT tank for treating but not necessary. If in dislay tank, remove your skimmer cup but leave the skimmer running as prazi-pro will make your skimmer go nuts. It will produce a truly amazing amount of bubbles so still have your skimmer running to keep the oxygen levels high in the water as some medications like praz-pro can lower the amount of oxygen in the water which is something you want to avoid so I recommend running an airstone in addition to treatment.
Also . . . remove any type of carbon that you have running to allow Prazi to run at full strength which will be 8 day interval, change water and treat again for one more 8 day interval.
