A pH probe<\/a> is an electrochemical sensor that measures the concentration of hydrogen ions (H\u207a) in water. It is a glass probe consisting of a measuring electrode (a pH-sensitive glass membrane) and a reference electrode (usually a silver\/silver chloride wire in a 3M KCl solution). The potential difference between the two is converted into a pH value.<\/p>\n The glass membrane and the reference electrode become contaminated over time by minerals, grease and disinfection by-products. This causes the measurement to drift. In pool water this happens faster due to chlorine, limescale and sunscreen. Without calibration, a deviation of 0.1 to 0.3 pH can already lead to incorrect dosing of chemicals, resulting in cloudy water, reduced chlorine effectiveness and corrosion of equipment. In a swimming pool, the pH should be between 7.2 and 7.6: that is where chlorine works best and the water stays pleasant for skin and eyes. Advice: calibrate at least twice per season (at start-up and halfway through).<\/p>\n Measure \u2192 Compare \u2192 Dose<\/p>\n The pH probe continuously measures the pH in the pool’s pipe circuit. The controller compares the measured value with the set value. If there is a deviation, the dosing pump starts: pH- (acid) if the pH is too high, pH+ (base) if the pH is too low. Modern systems dose proportionally: the greater the deviation, the longer the pump runs. Always check the settings of your pH dosing system to make sure you never overdose. Most devices let you set a limit. Bear in mind that it will take several minutes or longer before the injected pH passes the measuring chamber again. It is better to make several small corrections than 1 large one.\u00a0<\/p>\n If there are deposits of algae, grease or limescale on the pH probe, it responds slowly. First clean with cleaning solution<\/a> for probes. Maximum 15 minutes. Then rinse with clean water. Demineralised water may be used for rinsing, never for storage. Vinegar or household products do not belong on a pH probe. Only calibrate after cleaning, never before.<\/p>\n What you need: pH 7 buffer solution<\/a> (calibration solution), pH 4 buffer solution<\/a> (or pH 10 buffer solution<\/a>, depending on the system), tap water or demineralised water, soft cloth.<\/p>\n Note: buffer solutions change value with temperature. Always consult the temperature table on the label and preferably calibrate at a temperature close to that of the pool water. So do not leave the bottles in the sun at the edge of the pool.<\/p>\n The glass membrane needs a hydrated gel layer to be able to measure H\u207a. Storing it dry breaks down this layer, causing the impedance to rise and the response to deteriorate permanently. 3M KCl<\/a> keeps the gel layer intact, prevents the diaphragm from drying out and is compatible with the reference electrolyte. Never store the probe in distilled water, tap water or a dry environment. Fill the protective cap<\/a> with KCl storage solution 3 mol\/l until the glass bulb and the junction are covered. When you winterise the pool, remove the probe from the measuring chamber and store it this way, protected from frost.<\/p>\n The exact pH value you need to calibrate your pH probe differs from manufacturer to manufacturer. Many systems use pH 7 as the neutral point, supplemented with pH 4, pH 9 or pH 10. Other systems require calibration at 4.01, 6.86 and 9.18; there pH 6.86 is the neutral point. Whether you calibrate at 1, 2 or 3 points is stated in the manual of your system.\u00a0<\/p>\n Below is an overview of the most common systems and the pH value you need.<\/p>\nWhy does a swimming pool pH probe need to be calibrated?<\/h2>\n
How does a pH probe work in an automatic dosing system?<\/h2>\n
Cleaning the pH probe<\/h2>\n
The complete calibration procedure<\/h2>\n
What you need to calibrate a swimming pool pH probe<\/h3>\n
Step-by-step plan: calibrating a swimming pool pH probe in 6 steps<\/h3>\n
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Storing a pH probe: why KCl?<\/h2>\n
Which pH value for calibrating a swimming pool pH probe?<\/h2>\n
Overview: brands, buffer solutions and pH values<\/h2>\n