Magnesium plays a vital role in reef aquaria: it helps maintain calcium and carbonate (composing the majority of measurable alkalinity) concentrations by limiting unwanted inorganic precipitation with each other. In the absence of adequate magnesium ions, calcium and carbonate ions bond rapidly, depleting their concentrations in the system and creating the false impression that heavier supplementation is required to re-establish the desired concentrations. No matter how much calcium is added, its natural seawater concentration of 412 ppm will never be sustained until the magnesium concentration begins to approach 1,290 ppm. Once the balance between calcium and magnesium has been established, subsequent calcium supplementation yields immediate positive results. Keeping magnesium within a range of 1,290-1,320 ppm will maintain the desired balance, and provides enough of the element to reef-building organisms for the formation of aragonite.
NēoMag is a naturally-occuring mineral of high purity. It is primarily formed abiogenically (via a number of geochemical processes) as opposed to by living organisms (such as corals and other aragonite-secreting organisms). NēoMag is ~13% magnesium by weight, as opposed to ~0.10% Mg by weight (on average) of aragonite. This being the case, NēoMag is a superb source of magnesium in reef aquaria, particularly those with sufficient magnesium demand to require frequent supplementation. It is best-employed in a calcium reactor at a ratio of ~9:1 aragonite:NēoMag by volume. NēoMag may also be used in secondary chambers of calcium reactors to help eliminate free CO2 that has not reacted with the aragonite media, thereby simultaneously reducing the propensity for pH to exist at a depressed level in the aquarium and increasing the rate of media dissolution, and hence magnesium supplementation.