I noticed tonight that one of my acan frags the tissue seems to be receding. My parameters are
Temp 78-79
Sg 1.024
Alk 9
Ammonia 0
Nitrite 0
Nitrate 5ppm
Phosphate .04
Calcium 380-400
Mag 1280-1300
I spot feed them 2-4 times per week and I don't notice any fish or invert harassing them. The frag just next to it is thriving with many new polyps growing. No other corals show any signs of stress

any help is appreciated.
Temp 78-79
Sg 1.024
Alk 9
Ammonia 0
Nitrite 0
Nitrate 5ppm
Phosphate .04
Calcium 380-400
Mag 1280-1300
I spot feed them 2-4 times per week and I don't notice any fish or invert harassing them. The frag just next to it is thriving with many new polyps growing. No other corals show any signs of stress

any help is appreciated.