Water hygiene in pools & spas

The basic prerequisite for healthy bathing and swimming is modern water treatment. Of course, the treatment result should be checked regularly, especially under the aspect of changing operating conditions, for example the number of bathers, weather conditions, type of disinfection, etc., in order to determine in the best case that the water treatment is optimal. In the case of deviations from the recommended target values for auxiliary hygiene parameters, measures can be taken to exclude a possible health risk from the outset.

What can be understood by the term auxiliary hygiene parameters? Hygiene is generally understood to mean measures to prevent infectious diseases - in this context, water treatment. Auxiliary parameters are parameters that can be used to measure water quality. The following is a brief digression into the significance of the most important detection methods:

Free chlorine

Free chlorine is considered an effective agent for disinfection and oxidation of pool water and spas. How often and how much chlorine must be added depends on how often the pool is used. Other factors include water temperature, sunlight and the addition of fresh water. The free chlorine formed in the water ensures a temporary disinfection effect and is virtually odourless. The recommended measuring range is between 0.3 and 2.0 mg/l depending on whether inorganic or organic chlorine (stabilised chlorine) is used. The measurement of the free chlorine parallel to that of the pH value is usually carried out with the pool tester.

Combined chlorine

The chemical reaction of free chlorine with organic impurities produces chlorine compounds, so-called compined chlorine or chloramines. These chloramines cause skin and eye irritation and cause the unpleasant "chlorine smell". Bound chlorine has hardly any disinfection effect. In order to kill or render micro-organisms harmless and break down combined chlorine, the pool water must be regularly chlorinated. The content of combined chlorine should be minimised (> 0.2 mg/l); ideally it should not be detectable.

Total chlorine

Total chlorine is the sum of free and combined chlorine. First the free chlorine is determined, then the total chlorine. The difference between the two values is the combined chlorine content.

pH value

The pH value indicates whether the pool water is acidic or alkaline and is essential for the disinfecting effect of free chlorine. If the pH value falls below 6.5 (acidic range), eye irritation occurs. Corrosion can also occur on metallic components. At pH values above 7.8 (alkaline range), free chlorine loses more and more of its effectiveness. This can lead to clouding of the water and lime deposits. A pH range between 7.0 and 7.4 is considered ideal.


Alkalinity is the acid binding capacity of the pool water. It is part of the total hardness and is also called temporary, i.e. transitory hardness. High values of alkalinity prevent strong fluctuations of the pH-value. High alkalinity makes it difficult to influence the pH value. At low alkalinity, even small additions of acids or alkalis can cause strong pH-value fluctuations. Alkalinity therefore affects the stability of the pH-value and the pH-value in turn determines the disinfection effect of free chlorine. The alkalinity should be set in a range of 100 - 160 mg/l calcium carbonate (CaCO3); this corresponds to approx. 6 - 9 degrees of German hardness.

Complete water analysis

The electronic pool tester is recommended for the demanding private swimming pool and/or whirlpool user who wants to determine all the auxiliary hygiene parameters listed above. This is a photometric measuring principle using reagent tablets with long-term stability. 

If all values are within the recommended measuring ranges according to the recommendations of the manufacturers of water care products, a maximum of perfect water quality on the one hand and the long-term maintenance of the building structure including all components on the other hand is given.