Reef Advantage Calcium, 4 kg / 8.8 lbs Raises Calcium And Maintains Magnesium And Strontium In The Reef Aquarium A Non Caustic Optimized Blend Of Ionic Calcium Designed To Restore And Maintain Calcium Levels Found In Natural Seawater Calcium and carbonates are essential to all coral growth, if either become deficient coral growth will cease followed by a rapid decline in health Does Not Have A Caustic Ph. And Will Not Deplete Magnesium, Used As Directed It Will Not Deplete Alkalinity 250 Grams Treats 2000 Us Gallons