Two Little Fishies Magnesium Concentrate is a solution that contains the element magnesium, an essential pH-stabilizing component of the seawater buffering system. Magnesium is also important for the operation of various cellular enzymes, and is a key component of the pigment chlorophyll and the functioning of photosynthesis in plants. Two Little Fishies Magnesium Concentrate replenishes the magnesium concentration with a seawater ratio of magnesium chloride and magnesium sulfate. It helps maintain optimum water quality for corals, coralline algae, macroalgae, seagrasses, and mangroves. 500 ml