Are you purchasing pre-mixed saltwater or are you mixing yourself? Either way you should test salinity, Alk, Cal, and mag of the water you are using for your water change, those parameters should match very closely to the water in your tank. Water changes are to add depleted trace elements and remove waste/contaminants. If you are mixing your own salt water what are you using for your source water, tap, bottled, or RODI? If you keep doing water changes and the parameters do not match your tank water you are only further throwing the balace of your Alk and Cal. Also are you running carbon, if so when was the last time you changed it? When i notice an issue with a coral i do a list of things to see what the issue is and i do all of my list. 1 test parameters alk, cal,mag, and salinity. 2 change carbon and any mechanical filtration. 3 a 10% water change, or more, with with water that has matching parameters to my existing tank water. If my alk or cal parameters were off during this process i adjust the timer on my dosing pumps to slowly bring the parameter that was off back to where ot needs to be over a few days. Usually within a week my coral will mend its self.
