I have 3 blue-green chromis in my tank. Normally they are highly active, zipping around in the upper water column in search of food. However one of them is now hanging listlessly in the upper corner of the tank, head up, normal breathing rate. Its dorsal and pelvic fins are ragged, not diseased looking like tailrot and finrot in freshwater fish, more like nibbled off. Tail is fine. I had a similar problem earlier when one of my two 3-stripe damsels was being overly aggressive and nipping the chromis. Caught him and returned him to LFS. Have never seen the remaining 3-stripe do the same behavior, he's rather docile. At that time the chromises actively hid in the rock work. Besides the 3 chromis and 1 3-stripe the other fish inhabitants are: 2 false perculas 1 mandarin 1 bi-colored blenny Have never witnessed any aggressive behavior between them. There is a single peppermint shrimp, completely nocturnal and a detrivore crew of small hermits and snails 40 gal wide breeder, lots of well established live-rock and water parameters good. Any ideas?