Keep your aquatic life healthy and thriving by testing your aquarium water's calcium levels regularly with this easy-to-use API CALCIUM TEST KIT for aquariums. Testing water parameters weekly helps prevent invisible water problems that can be harmful to fish. 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. The API CALCIUM TEST KIT measures calcium levels as low as 20mg/L. It contains two calcium test bottles, capped glass test tube, instructions & color card. For use in reef aquariums.