Calcium carbonate


CaCO3, is a White chemical

compound that is the most

common mineral. It occurs in two

crystal forms: calcite and

aragonite. Calcium carbonate is

largely insoluble in water but is

quite soluble in water containing

dissolved carbon dioxide,

combining with it to form the

bicarbonate Ca(HCO 3 ) 2



Hardness of water


Reluctance of water to produce a lather with soap, due to various dissolved salts, mainly those of calcium and magnesium.


Hard water is water that has high mineral content (mainly Calcium and Magnesium ions) (in contrast with soft water). Hard water minerals primarily consist of calcium (Ca2+), and magnesium (Mg2+) metal cations, and sometimes other dissolved compounds such as

bicarbonates and sulfates. Hardness may be temporary (removed from the water by precipitation on surfaces by boiling or heating) or permanent (not affected by boiling or heating). All bicarbonate salts contribute to temporary hardness. All other salts contribute to permanent hardness. Total hardness is the sum of the two.


Salts contributing to permanent hardness:Calcium chloride, Calcium sulphate, Magnesium chloride, Magnesium sulphate.


Salts contributing to temporary hardness: Calcium bicarbonate, Magnesium bicarbonate.In other words: Salts containing CO3




Hardness levels


Very soft: 0-70 ppm, 0-4 dGH

Soft: 70-140 ppm, 4-8 dGH

Slightly hard: 140-210 ppm, 8-12 dGH

Moderately hard: 210-320 ppm, 12-18 dGH

Hard: 320-530 ppm, 18-30 dGH

Very hard >530 ppm, >30 dGH


PPM (Parts Per Million) and defined as CaCO3 per liter.


dGH (degrees General Hardness) same as degrees German (°D) and defined as CaO per liter. 1 gDH = 10 mg/liter as CaO.1 gDH = 17.778 PPM as CaCO3


French degrees (°f)

One degree French is defined as 10 milligrams of calcium carbonate per liter of water, equivalent to 10 PPM.


Conversion French degrees to German degrees.


1 °f= 10 PPM and 1 °D = 17.778 PPM

Therefore 1 °f = 0.56 °D