- Simple and reliable monitoring of the water values in aquariums and ponds. Determines the ideal carbonate hardness in fresh and marine water - Colour change test: fill plastic cuvette with sample water, add reagent drop by drop until colour changes from blue to yellow. Number of drops = level of carbonate hardness - When to use: for setting up a new aquarium: once a week, afterward once a month -Package contents: 1 KH quick test, incl. one reagent and plastic cuvette.