Salifert's Oxygen Test Kit provides you with a quick and accurate reading of one of the most vital (and difficult to test) parameters of your aquarium: oxygen itself. Knowing how much oxygen is mixed into your saltwater aquarium's water is highly important for healthy corals and other marine fish, which require oxygen concentrations at saturation level in order to survive. The low solubility of oxygen in saltwater (approx. 5-7 ppm) can make it difficult to maintain an adequate amount. This makes oxygen tests a valuable and sometimes crucial tool for marine aquarium owners with complicated systems, including users of calcium reactors and CO2 systems, which may deplete or alter the oxygen levels of your aquarium as a side effect. Contains 50 tests, and can be used to test the oxygen levels in both freshwater and saltwater aquariums as well as ponds.