How to balance your pool's pH: step-by-step guide
The pH of pool water is the parameter that most influences the effectiveness of water treatment, the comfort of swimmers and the preservation of all pool materials, including the PVC reinforced liner. Incorrect pH can make chlorine ineffective, irritate eyes and skin, or prematurely deteriorate the lining. However, correcting it is surprisingly simple if you know how.
What is the ideal pH for a pool?
The optimal pH range for pool water is between 7.2 and 7.6. This range is not arbitrary:
— For comfort: The natural pH of the human eye and mucous membranes is approximately 7.4. Water with pH in this range does not irritate the eyes or skin.
— For chlorine effectiveness: Active free chlorine (hypochlorous acid) is much more effective as a disinfectant at low pH. At pH 7.0 chlorine is effective in ~73%; at pH 7.5, in ~48%; at pH 8.0, only in ~22%. High pH means needing much more chlorine to achieve the same disinfection.
— For material protection: Excessively acidic pH (below 7.0) can attack stair metals, discolor PVC liner and corrode filtration system components. Very basic pH (above 7.8) promotes scale buildup and water turbidity.
How to measure pH
There are three main methods:
Colorimetric test with reagent (DPD): The most economical and widely used. A few drops of reagent are added to a water sample and the color is compared to the scale. Accurate if done correctly, but requires buying reagents periodically.
Test strips: Quick and easy to use, although less accurate than the colorimetric method. Useful for quick checks between more detailed measurements.
Digital pH meter: The most accurate method. A mid-range pH meter (€20-80) offers exact readings to the tenth and is the system preferred by professionals. Requires periodic calibration with buffer solutions.
It is recommended to measure pH at least 2-3 times per week in summer and once per week in the rest of the year.
How to raise pH
If the pH is below 7.2, you must raise it. The most common product is sodium bicarbonate (pH+), which also has the benefit of increasing total alkalinity, acting as a buffer that stabilizes pH. Sodium carbonate (soda ash) can also be used, which raises pH more quickly but with more risk of exceeding the limit.
The indicative dose of sodium bicarbonate is 150-200 g per 10 m³ of water to raise pH by 0.2 units. It is always recommended to add in small doses and remeasure after 4-6 hours.
How to lower pH
If the pH is above 7.6, you must lower it. The most commonly used product is diluted hydrochloric acid (also called muriatic acid or pH-), which acts quickly. There is also sodium bisulfate powder, a safer alternative to handle. Muriatic acid is more economical but requires precautions: gloves, goggles and always add it to the water (never the reverse) in small quantities.
The indicative dose of muriatic acid (33%) is 250-400 ml per 50 m³ to lower 0.2 pH units. As with raising, it's better to dose in multiple batches and remeasure between them.
Common mistakes
— Adding chlorine without verifying pH first: If pH is high, chlorine will be practically ineffective and you're wasting money.
— Measuring immediately after adding correctors: Wait at least 4-6 hours with the pump running before measuring again.
— Correcting only pH without checking total alkalinity: Alkalinity (ideal between 80-120 ppm) acts as a pH buffer. Low alkalinity makes pH unstable and will rise or fall drastically with small product additions.
— Adding too much corrector at once: It's always better to dose in small amounts and verify the result.
Impact on reinforced liner
Quality PVC reinforced liners are resistant to a wide pH range. However, prolonged exposure to extreme values (pH below 6.5 or above 8.5) can affect the color and flexibility of the liner over time. Maintaining pH in the optimal range not only protects swimmers and optimizes treatment, but also helps extend the useful life of the lining for many years.
Do you have persistent problems with the pH or water in your pool? Our team of specialists can analyze your pool water and recommend the most appropriate treatment to achieve perfectly balanced water. Contact us.
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