1—75
pH, continued
Standard Calibration Adjust
To perform a standard calibration adjustment using the pH 7.0 buffer, see Standard
Calibration Adjust on page 2—13.
Summary of Method
Proper pH control in drinking water and swimming pools is necessary for many
reasons. Bactericidal activity of chlorine is greatest when the pH is less than 7.4.
Alum-type flocculents, important for clear water, perform best in a pH range of 7.2
to 8.0. Keeping the pH below 8.0 is important to control algae. A sudden rise in pH
may signal an increase in algal growth. If the pH drops below 7.0, corrosion of
pipes and metal fixtures may occur. Eye irritation is minimized when the pH is kept
between 7.2 and 7.6.
Phenol Red is a phthalein indicator which has a transition window of pH 6.8
(yellow) to 8.2 (red). The pH is determined colorimetrically from the change in the
absorbance of the alkaline peak.
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