Contains one (1) API CARBONATE HARDNESS TEST KIT Aquarium Water Test Kit, including 1 bottle of testing solution, 1 colour card and 1 glass test tube with cap Helps monitor water quality and prevent invisible water problems that can be harmful to fish and plants and cause fish loss Accurately measures carbonate hardness in freshwater and saltwater aquariums KH (Carbonate Hardness) stabilizes aquarium pH. Use weekly for monitoring and when water or fish problems appear