General features of the water of a swimming pool

Active chlorine

This is the chlorine available for disinfection; it depends on the pH. E.g.: at a pH of 7.2 the chlorine is active at 70%. At a pH of 7.8, it is now only available at 30%.

Active oxygen

Disinfecting oxidising agent contained in products such as hydrogen peroxide or mono potassium persulphate. Very active against micro-organisms, it does not, however, produce a long-lasting impact. It should be used in conjunction with another product, known as an activator, which makes the treatment more long-lasting.


They present no danger for man; they are only harmful to the aesthetics of the water. However, they carry organic matter which absorbs disinfecting products. They consume carbon dioxide, which is acidic, and as a reaction the pH increase. They generally hook onto the seals of tiles and once they have fully developed, they are very difficult to eliminate. Their appearance shows the insufficiency of disinfection, but the opposite is not true.


Most often emitted by swimmers. The risk of infection essentially stems from pathogenic Staphylococcus from the ENT area. They are emitted in water wrapped in mucus which protects them from disinfectants. They concentrate in the superficial layer of the water and the skimming of the surface by discharge spouts makes it possible to eliminate them.


Oxidising agent from the family of halogens; like chlorine, it disinfects. Extracted from sea water or saline sources, bromine is less aggressive than chlorine for the skin, eyes and hair. It is less sensitive to pH and will retain its effectiveness up to a pH of 7.8. Recommended especially for heated tanks where the temperature favours the rise in pH.

Buffer effect

Essential to prevent excessive pH variations, the buffer effect is obtained with a properly adjusted total alkali strength.

Combined chlorine

This is the result of the destructive action of the chlorine on the components that it attacks by oxidation. It is also known as chloramine. It is not active on the micro-organisms to be treated. Only with a regular shock treatment is it possible to reduce the combined chlorine and render the chlorine sufficiently active again.

DPD tablets

Testing kit to check whether the chlorine present in the water is an active chlorine or not. DPD No. 1 determine free chlorine, DPD No. 2 mono chloramines; DPD No. 3, di and tri-chloramines and DPD No. 4, total chlorine (active + reserve + chloramines). Only DPD No. 1 tablets are useful for private pools.


Aluminium or iron sulphates make it possible to lump together micro-particles present in the water so that they are retained by the filtration system. It improves the sharpness of the filtration system. Not advised for diatomaceous filters. This takes the form of ACTI FLOC or FLOVIL.

Health and safety inspection record

A compulsory document for the management of a communal swimming pool, this record includes all the routine elements linked to the everyday life of the swimming pool (filtration cycles, water temperature, pH, content of disinfectant etc.).

Inorganic chlorine

This is chlorine without any cyanuric acid or stabilising agent.

Oxidisable substances

This is the content of organic matter. It should be as low as possible and generally under 5 mg/l of O2 and if possible nearing 1 mg/l to prevent the consumption of the disinfection product.

Parasites (fungi and amoeba)

The main risk linked to fungi is interdigital mycosis which is transmitted by floors and wooden benches. The risk related to amoeba is very rare, but the possible transmission of a variety of amoeba should be noted which passes on primitive amoebic meningo-encephalitis which are generally fatal. Warm water favours the growth of amoeba.

pH or potential hydrogen

Enables the degree or acidity or alkalinity to be determined in the water You are usually advised to maintain the pH between 7.2 and 7.4. A pH above 7.8 causes scale to form on the equipment, discomfort to the swimmers as it is aggressive for skin and the development of bacteria and algae which feed on lime and magnesium. An acid pH less than 7 causes corrosion. The pH is measured using an electronic tester, Aquachek Silver 7-way tests, for instance.


Polyhexamethylene biguanide: algaecide which has a flocculant capacity. Its action must be combined with an oxidiser like the hydrogen peroxide. The use of the PHMB in a chlorine pool requires the chlorine to be neutralised in advance (with ACTI Stop). Conversely, a pool treated with PHMB which will turn into chlorine requires the pool to be fully drained.


This abbreviation stands for part per million; it is a measurement standard for a number of different rates. It actually corresponds to mg/l or g per m3.

Scale remover

Enables the elimination of lime deposits which clog up pipes and feed algae.

Shock the water

This is an additional action on the water corresponding to disinfection. Shocking the water prevents the accumulation of contaminating agents, optimises the action of the disinfectant, minimises the rate of chloramines and improves the clarity of the water. With this in mind, shock chlorine or shock bromine must be used making sure to adjust the PH according to the treatment (ideal 7.2 to 7.4 for the chlorine and 7.2 to 7.8 for the bromine).

Sodium chloride

This is the salt that is placed in the water and which will turn into sodium hypochlorite by electrolysis and thus enable the tank to be disinfected. The salt should be as pure as possible so as not to prematurely damage the electrode or mark the liner

Suspended matter

The swimming pool water should contain as little as possible.

The potential hydrogen (pH)

It must be between 6.9 and 8.2, with the ideal figure being 7.4 (average pH of the lacrimal fluid).

The total alkali strength

In swimming pool water, this is the bicarbonate content. It represents the buffering power of the water. Water with a weak total alkali strength will undergo strong pH variations. The ideal value is situated between 10°F and 30°F. Generally, the total alkali strength is slightly higher than the TH.

The total hardness (TH)

The hardness of the water is ideally situated between 10°F and 20°F.

Total chlorine

This is the amassed free chlorine and combined chlorine. The total chlorine and free chlorine may be measured using Aquachek Silver 7-way tests.


In the water, the risk of a virus being transmitted is almost non-existent (they do not reproduce in the water and are generally quickly destroyed by disinfectants). The main risk is linked to the virus of plantar warts (papillomavirus) transmitted by floors accessible to swimmers with bare feet (beaches, dressing rooms and showers).