Red Sea Fish Pharm ARE22033 Reef Foundation Magnesium Supplement-C for Aquarium, 500ml Reef Foundation C Contains Blended Salts Of Magnesium And Is Part Of Complete Reef Care System Calcium, Magnesium, Strontium And Carbonate Are The Basic Foundation Elements Of Coral Skeletons All of these elements need to be available in balanced proportions for coral health and growth Includes A Convenient Measuring Cup For Easy Dosing Available In 500-Ml Bottle