[How to use] This product is a qualitative reagent for all hardness (American hardness) of pure water. Add 1 drop of this product per 0.3 fl oz (10 ml) of pure water to measure. Shake well and immediately check the color of the item. Color Complimentary Requirements: Approximately 0.6 oz (2 mg/L) of water and under: Blue; Approximately 0.6 oz (2 mg) / L and above: Red. Please use it as an estimate for replacing ionic replacement resins in pure water manufacturing equipment. Storage Instructions: Close the cap and store at room temperature away from sunlight and humidity.