Water Hardness

Calcium () and Magnesium () are the two most common ions that are found in hard water, while iron (Fe2+), Manganese (Mn2) and Aluminium (Al3+) can also contribute to hardness.

Hardness is defined as the sum of the calcium (Ca2+) and magnesium (Mg2+) concentrations, both expressed as calcium carbonate in milligrams per litre (mg/l).   Iron (Fe2+), manganese (Mn2+) and Aluminium (Al3+) can also contribute to water hardness.

The water hardness has a significant effect on the performance of compounds. Soft water will cause foam; hard water will increase the compound usage and can cause spots on component parts during drying.

Units of Measure

Water hardness measures the concentration of Ca2+ and Mg2+ ions and is recorded as: –

  • Grains per gallon (gpg)
  • Parts Per Million (ppm) = Milligrams per litre (mg/l)
  • Degrees Hardness – German (ºdH)

1 gpg + 17.1.mg/l = 17.1 ppm = 1.7ºdH

Water Hardness is measured on a linear scale. One (1) gallon of soft water (0 grains per gallon) mixed with one (1) gallon of very hard water (20 grains per gallon) makes two (2) gallons of medium hard water (10 grains per gallon).

Water Hardness

Water Hardness Table (sb) cropped

Water hardness adjustments

When we (Rὅsler) recommend compound and water settings please note that these are usually based on trials we have run in test facilities. Should you experience issues such as excessive or too little foam then you should talk to us so we can help adjust your settings to compensate for any variation in your water hardness.

For further assistance complete the online form at www.rosler.com



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