Easily and accurately measure calcium levels to maintain a healthy saltwater aquarium with API Calcium Ca Saltwater Aquarium Test Kit. Calcium is one of the most important elements in a reef aquarium. Corals, crustaceans, mollusks and some types of encrusting algae need calcium for skeletal growth. The more calcium these organisms use, the lower the levels, making testing an important part of your maintenance routine. This kit uses the titration method to measure calcium levels as low as 20 mg/L. Just fill a test tube with aquarium water, add a few drops of Calcium Test Solution Bottle #1 and shake until the solutions turns from pink to blue. Then compare your results with the color chart and follow the included recommendations if action needs to be taken. Kit comes with glass test tube, liquid test and color chart. For saltwater tanks only.