Reef Endurance Bulk Magnesium Chloride 30lbPharmaceutical Grade Magnesium Chloride Aquarium Supplement Reef Endurance Magnesium Chloride is a pharmaceutical based aquarium supplement that mixes crystal clear with no unwanted impurities. In reef aquaria, maintaining a proper magnesium level of 1200 1350ppm helps achieve the essential balance of calcium and alkalinity in the aquarium by preventing excess calcium carbonate precipitation. For best results, use in conjunction with Reef Endurance