i bought this tang last sat. he still hasn't eaten and he is not swimming much. he kind of chills in one spot kind of twiching ever once in a while. his color now kind of looks bad like darker grey splotches one his body and his back fin has a missing piece off the bottom. any one know what could be the problem. i have tried to feed formula 2 flakes, frozen brine shripm (LFS
fed this), and formula 1 frozen.