Calcium is one of the most important elements in a reef aquarium. Reef invertebrates such as corals, crustaceans, molluscs and even some types of encrusting algae need calcium to grow and remain healthy. Over time, calcium levels drop as invertebrates use it 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 colour change for precise measurement.