Sodium hypochlorite / 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 to activate the free chlorine. 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 or 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.