The water has become too salty??
Salinity creep is a common problem with marine aquariums, even though the tank may have been regularly topped up with fresh water to replace the evaporated water. Salt water collected in-shore is saltier than normal, often as high as 1.025 (optimum is around 1.022). Consequently, every time a water change is made the salinity creeps up. SO, during every water change, check the salinity with a hydrometer and add additional fresh water as needed. NOTE: Allow a good time (like 30min) for the fresh and salt water to mix properly before testing each time.
