Operating instructions
CF Control 100
1.6 Information about carbonate hardness (CH)
The carbonate hardness (also acid capacity K
s 4.3
) is a factor that was not considered in
the treatment of swimming pool water for a long time – it must not be confused with the
total hardness of water!
Carbonate hardness only forms in connection with hydrogen carbonates. When heating
water, CO2 escapes and lime (calcium carbonate CaCO3, which is of low solubility)
precipitates. As a result, the pH level increases, while the carbonate hardness or acid
capacity, respectively, decreases. This in turn, has an adverse effect on the effectiveness of
the flocculant, which is reduced, while the consumption of the pH reducer and the
aggressiveness of the water increase.
Recommended values for
KS 4.3
to DIN 19643:
Swimming pools min. 0.7 mmol/l approx. 2° CH
Whirlpools min. 0.3 mmol/l approx. 0,8° KH
In filling-water that was treated conventionally for several weeks, the carbonate hardness
permanently goes down and thus the acid capacity decreases. Even hard types of water can
therefore have an insufficient acid capacity (K
S 4.3
) within a short time.
Even an adequate fresh water supply (hard water) according to DIN 19643 will not be
sufficient in the long run to stabilize an ideal acid capacity. Experience has shown that pool
owners try to cut down expenses by using less fresh water, in particular in the private sector.
If the fresh water is too soft, the hardness of the pool water must be increased with
appropriate hardness stabilizers (carbon dioxide, carbonic acid, calcium carbonate, sodium
hydrogen carbonate etc.). Ask for information about our pH stabilizer products.
Why is it very important to comply with the values for carbonate hardness?
Electrodes (combination electrodes) are used for a continuous measurement of
chlorine, redox and pH values. These electrodes consist of a measuring unit, a
reference unit, a special electrolyte filling and a diaphragm. With the help of this
diaphragm, an exchange of molecules takes place between the hydrogen in the pool
water and the electrolyte molecules. The ratio of this is disturbed in case of a lack of
carbonate hardness; i.e. the internal buffer of the reference system is depleted.
Result: The electrode will not work any more and cannot be calibrated any longer!
When the electrode is replaced, the same will happen after a short time.
If an acid capacity of approx. 1.8 mmol/l (carbonate hardness = 5° dH) is maintained, a long
operational safety of the electrodes (combination electrodes) can be assumed.
There are diverse measuring instruments available for measurement of the carbonate
hardness.
Quick test for carbonate hardness, e.g. dinotec Easytest carbonate hardness, order no.
1420-022-00.
Ideal value
1.8 mmol/l = 5° dH
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