The JBL ProAqua Test MgCa Magnesium/Calcium is an easy to use drop test to measure the magnesium and calcium content of saltwater. As the magnesium content can only be measured by recording the sum of magnesium plus calcium, the two tests have been combined in one pack. The magnesium content can be calculated by subtracting the calcium content from the total value of Mg + Ca.Why test? Invertebrates (stony corals and soft corals, sponges, sea urchins, crustaceans, mussels, snails etc.) and the popular red coralline algae found in marine water require sufficient levels of calcium for healthy growth. The natural calcium level of the sea is 390-440 mg/l. In order for the organism to make the best use of the calcium, the correct ratio of hydrogen carbonate must also be present in the water. For this reason adding calcium compounds without hydrogen carbonate (such as calcium chloride), is pointless. A calcium level of 400-480 mg/l has proved to be ideal for marine aquariums. In addition to c