... 0.4-20mg/L (calculated as CaCO3) Packing: 50 tests/box Fast, Easy-to-Use, Accurate Low hardness of water Test ... least 1 year 2. FeatureConvenient to use:Light weight and small size, suitable for detection on site, and minimize the ... agent, etc; Standardized precise colorimetric cards specialized for colorimetric tubes; Double layers aluminum foil, preventing moisture and light.3. Operation1. Use the ...