Calcium is one of the most important elements in a reef aquarium. Reef invertebrates such as corals, crustaceans, mollusks and even some types of encrusting algae need calcium to grow and remain healthy. Over time, calcium levels drop as invertebrates use calcium in aquarium water. This kit allows you to easily and accurately measure calcium levels and maintain a healthy reef aquarium. Measures calcium levels as low as 20mg/L Uses titration method, with easy to see color change for precise measurement. For use in Saltwater Aquariums or Ponds Monitoring calcium levels is essential for keeping a successful reef aquarium. Reef organisms use calcium to build a calcium carbonate skeleton. Over time, as the calcium in the water is utilized, the calcium level will gradually drop. Calcium must be present for corals to grow. Even reef invertebrates such as crustaceans, mollusks and encrusting algae require calcium to grow and remain healthy. Kit contains: two dropper bottles for accurate dispensing of test solutions, easy to read instructions and a color chart, a non-staining glass test tube with snap-tight cap. This is a titration test kit, results depend on how many drops are used until the solution turns blue.