If you want to maintain the ideal reef tank parameters, you will need to test and supplement calcium, alkalinity, and magnesium. Corals deplete calcium, alkalinity, and magnesium as they grow. Keep the best reef tank parameters to keep your corals healthy: Ca 420, Alk 9 dKH, Mg 1350 is a good target. As alkalinity drops, the pH in the aquarium also drops, which can damage your fish and coral. Reef tank calcium levels must be maintained or corals will not grow. So, be sure to test and supplement often. Even fish only with live rock (FOWLR) systems should be dosed for the coralline algae. Many hobbyists now use reef dosing pumps to automatically replenish major elements.
Brightwell AquaticsChaeto Algae Refugium Fertilizer - ChaetoGro - Brightwell Aquatics
Brightwell AquaticsBrightwell Aquatics Kalk+2 - Advanced Kalkwasser Supplement
Brightwell AquaticsBrightwell Aquatics Ph+ Liquid pH Increaser Marine