pH (= acidity)
The pH (= acidity) is the most important parameter to measure in your swimming pool or spa.
The value should be between 7.0 and 7.6; 7.2 is ideal.
- Too high a pH value can result in the development of dangerous bacteria such as Pseudomonas, because the chlorine chlorine in your pool water is much less active. Clear water is not always a guarantee for the absence of dangerous bacteria or viruses. That is why measuring the pH is very important for the health of your children and yourself. In addition, too high a pH value in combination with too little free chlorine will lead to algae growth (green water).
- Too low a pH value can lead to corrosion of all metal parts (stairs, ladders, heat pumps, circulating pumps, lighting etc…) and the development of the irritant chlorine odour (trichloramines), which causes eye, nose and skin irritations.
Attention: The pH value of your water (especially in case of a spa) must always be measured when your water has reached the right temperature (37°C for a spa). After all, the pH value will rise as the temperature of your water increases (the pH rises as carbon dioxide escapes). Adjusting the pH value of your water is useless if the temperature has not yet reached the desired level, since it will change as the water is heated.
Chlorine (= free active chlorine)
The presence of chlorine in your pool or spa is necessary to ensure that the water stays clear and healthy (oxidised and disinfected water).
The chlorine in your pool water that should be measured is the free chlorine (which prompts the oxidation and disinfection).
The following concentrations of free chlorine should be maintained to be 100% certain that your water is sufficiently oxidised and disinfected (clear and free of bacteria and viruses).
- Outdoor swimming pool: 0.5 to 3.0 mg/l
- Indoor (roofed) swimming pool: 0.5 to 1.5 mg/l
- Spa or whirlpool: 1.0 to 3.0 mg/l
The pH should be between 7.0 and 7.6, so that the free chlorine chlorine is active. Too high a pH value (> 7.6) will make your free chlorine inactive (your water could even turn green).
Attention: The use of chlorine tablets and granules that contain cyanuric acid (mono–, di–, or triisocyanurate ions) will cause the concentration of active free chlorine to be much lower than the measurements with a photometer indicate.
The cyanuric acid level must not exceed 70 mg/l, otherwise your free chlorine will not be active enough anymore.
Liquid chlorine chlorine bleach lye is sodium hypochlorite = NaOCl
The concentration used by qualified installers is 13% = 130 g/l=ppt or 130,000 mg/l=ppm
Attention: Never mix liquid chlorine directly with an acid = pH-minus, because it will immediately release chlorine gas (a green cloud) which is extremely harmful to your lungs and may even cause death in case of high concentrations.