API MARINE MAGNESIUM raises and restores magnesium levels in your reef aquarium, and should be used whenever magnesium deficiency is present in your water. The magnesium level of a reef aquarium should be between 1,250 1,450 ppm. Use API MARINE MAGNESIUM when water tests show a magnesium level below 1,250 ppm mg/L in your reef aquarium. Dose according to directions on product label. Treats up to 948 US gallons of salt water. With API Aquarium products, its easy to keep a beautiful saltwater, freshwater or reef aquarium. For over 50 years, API has been creating innovative, research-driven solutions that make it easier to care for your fish and aquarium. API Aquarium Treatment Supplies are designed to work in conjunction with each other to provide best results to control algae, promote healthy bacterial growth and help control and cure fish diseases and conditions such as ich and fin rot.