Calcium Test Kit is helpfull to determine calcium level in Boiler, Cooling, Aquarium Water. Very simple to use can be handle by simple colour determination test 

For Example
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 reef aquariums