Calcium Reactors for saltwater aquariums are by far the best way to control and ensure proper trace element concentrations. By dissolving dead coral skeletons, calcium reactors will release the trace elements in proper ratios for coral growth in a saltwater aquarium. Calcium reactors do require CO2 injection along with pH monitoring, but on a properly set up system, calcium reactors require very little maintenance, are reliable, and the media is much cheaper than 2-part additives.