dying hammar

I’ve had my hammer coral for over a week now, 3 days ago it was open and full then it didn’t open 2 days ago. I will include info below. Tank: 52 litres/ 13.5 gallons Flow: low to moderate Ammonia: 0 Nitrate: 2 Nitrite: 0 Ph: 8.2 Mag: 1450 Cal: 480 Kh: 7 My acan coral is doing well inside...