Water Hardness - Water Quality Parameter Overview | Hach
When the water hardness test strip is dipped in a water sample, a color develops on the strip and the strip is matched to a chart. The chart shows colors for concentrations of 0, 25, 50, 120, 250, and 425 ppm, or 1, 1.5, 3.7, 15, and 25 gpg. Use the test strips when a general range for hardness is sufficient.