Brightwell Aquatics - MAGNESION-P. High-purity powdered magnesium blend. Provides magnesium, which helps regulate the balance between calcium and carbonates in aquarium water, and is a component of aragonite, the mineral secreted by reef-building organisms to form skeletal material. Stronger and more economical than liquid magnesium solutions; created for hobbyists maintaining multiple reef aquaria. Formulated by a marine scientist. Powder. 300-g.