Water Hardness in Swimming Pools: The Complete Guide
Origins of Water Hardness
Rainwater, by absorbing CO2 from the atmosphere, becomes acidic and capable of dissolving limestone from rocks. In France, where 70% of the territory contains limestone, the water hardness in some departments can reach 40 to 50°f. Conversely, regions like Brittany or the Massif Central, with little limestone, exhibit low hardness.
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Measuring Hardness
The concentration of calcium ions can be measured using:
- A photometer and a CALCHECK pill.
- A graduated test tube and the TH Test pill.
- A drop counting method.
- Test strips or test bands.
It is important not to confuse the pills for the photometer with those for the graduated test tubes, as they are different.
Definition and Measurement Units of Hardness
The measurement of hardness, called Hydrotimetric Title (TH), can be expressed in ppm, °f, °dH (German degree), or °e (English degree). 1°f corresponds to 10 ppm, equivalent to 10 g/m3 of Calcium Carbonate (CaCO3).
Disadvantages of Hard Water
Waters rich in Ca2+ and Mg2+ ions cause many problems, such as limestone deposits on walls, scaling of pipes, and irregularities in the operation of pool equipment. This excessive hardness can also reduce water transparency and cause skin or eye irritation.
Disadvantages of Soft Water
Soft waters, common in granitic or volcanic regions, can be aggressive towards cements and cause corrosion of metal parts. However, they are pleasant for the skin and hair.
Recommended Water Hardness
The recommended hardness varies by region: in France, a TH of 15°f is the minimum for potable water. For pools, a TH between 10°f and 20°f is ideal, while more than 40°f is considered excessive.
Natural Increase of TH
Evaporation concentrates calcium ions, increasing the TH over time. Precipitation can moderate this evolution, but is often irregular and insufficient to completely stabilize the TH.
Impact of Disinfection Products
Disinfectants like calcium hypochlorite increase the TH by adding calcium ions to the water. In very hard waters, the use of this type of product is discouraged.
Correction of Too Low Hardness
A low TH can be corrected by adding calcium chloride, either dehydrated or hydrated, depending on the specific need to increase it.
TH Analysis
Analysis methods include the use of CAL Test pills with a graduated test tube. Test strips or test bands can also provide a quick indication of hardness.
Softening of TH
Softening can be achieved by eliminating calcium ions, preventing the formation of carbonates, or using agents that trap these ions to delay scaling.
