pH value | 6.5 - 8.4 mg/l (ppm) | reagent for measurements - Phenol Red.
The pH (potentia Hydrogenii) value is a measure of the strength of the acidic and/or base effect of a watery solution. It is particularly important when preparing bathing water because, among other things, it influences the effectiveness of disinfectants and the compatibility of the water with skin, eyes, and materials. A pH value of 5.5 is ideal for the skin. However, the water would then have so much acid that metallic materials would not only corrode but eyes would start to burn because tears have a pH value of between 7.0 and 7.5. therefore, a compromise must be found. In regard to materials compatibility, the pH value shouldn’t fall below 7.0 in any case. At the same time pH values over 7.6 will have dermatological effects and will also influence the effectiveness of the disinfectant, thus negatively influencing the speed at with which bacteria can be killed off. Principally: At pH values above 7.5 = the natural coat of the skin that protects against acids begins to be destroyed (>8.0); in (medium) hard water, calcium precipitation beings (>8.0); the disinfecting effect of chlorine declines with (>7.5) pH values under 7.0 = chloramines form which irritate the mucous membranes and cause irritations to the sense of smell (<7.0); corrosion appearances in metal-content (installed) parts (<6.5); problems with flocculation (<6.2).