A swimming pool’s pH measures its acidity or alkalinity on a scale of 0 to 14. For swimmer comfort and sanitizer effectiveness, the ideal pH range is slightly alkaline, specifically between 7.4 and 7.6. When the pH climbs above this range, it is considered high, causing several problems. High pH reduces chlorine effectiveness, making the pool less sanitary and allowing bacteria to multiply. This imbalance also causes skin and eye irritation, cloudy water, and the formation of scale deposits on pool surfaces and equipment.
Understanding Why Pool pH Rises
The primary reason pool pH tends to drift upward is a natural process called carbon dioxide (CO2) off-gassing. Pool water contains dissolved CO2, which forms carbonic acid and contributes to a lower pH. When the water is agitated or exposed to the atmosphere, this dissolved CO2 escapes into the air, similar to how a carbonated drink goes flat. As CO2 leaves the water, the carbonic acid concentration decreases, causing the pH level to rise.
This off-gassing process is significantly accelerated by aeration features like waterfalls, fountains, and jets. Total Alkalinity (TA) also plays a substantial role, acting as a buffer that resists pH changes. If the TA level is high, it creates a stronger pull toward a naturally high pH equilibrium, often between 8.2 and 8.6. This means the pH rebound happens faster after an acid addition.
Other factors also contribute to a rising pH, including the introduction of high-pH source water, such as municipal or well water. Many common pool chemicals, like chlorine shock (sodium hypochlorite), have a naturally high pH and will cause the pH to increase upon addition. CO2 loss is the main driver, and understanding this is key to effective long-term management.
Applying Household Acids to Adjust pH
Some homeowners explore using common household acids like distilled white vinegar to lower pool pH, seeking a gentler alternative to commercial pool acids. Vinegar, or acetic acid, has a low pH (typically between 2.0 and 3.0) and will technically lower the water’s pH. The chemical reaction introduces hydrogen ions that neutralize the alkaline substances in the water, similar to stronger acids.
Household vinegar is highly diluted, typically only 5% to 8% acetic acid, making it very weak for pool chemistry purposes. To lower the pH by just 0.1 units in a 10,000-gallon pool, one would need to add around one gallon of vinegar. This requirement of 5 to 10 gallons of vinegar for every 10,000 gallons of water makes the method impractical and expensive for large pools.
Using large volumes of vinegar introduces an excessive amount of organic matter (acetate ions) into the pool. This organic load consumes the chlorine sanitizer, potentially leading to cloudy water or promoting bacterial and algae growth. Therefore, while vinegar is a natural acid, it is only feasible for minor, temporary adjustments in very small bodies of water, such as hot tubs.
Water Feature Adjustments and Alkalinity Control
The most effective non-chemical approach to managing a naturally rising pH involves controlling the factors that accelerate CO2 off-gassing. Pool features that spray, splash, or circulate water vigorously, such as waterfalls and aerators, increase the water’s surface area exposure to the atmosphere. Temporarily turning off these aerating water features slows the rate at which CO2 escapes, thereby slowing the pH drift upward.
A more sustainable long-term strategy is precise management of Total Alkalinity (TA), which serves as the pool’s buffering capacity. When TA is high, it holds the pH steady at a higher level, requiring constant acid additions to maintain the ideal range. By intentionally lowering the TA level, the water’s resistance to pH change is reduced, allowing the pH to stabilize more easily at a lower set point.
The ideal TA range is generally 80 to 120 parts per million (ppm). For pools that experience rapid pH rise, maintaining TA toward the lower end, around 80 ppm, is recommended. This lower TA range allows the pool to maintain a more stable pH without constant adjustment, achieving long-term, natural pH stability.