A swimming pool’s water chemistry is defined by its pH level, which measures how acidic or alkaline the water is on a scale of 0 to 14. The ideal pH range is slightly alkaline, typically maintained between 7.4 and 7.6, as this range closely matches that of the human eye and skin. When the pH level rises above 7.8, the water is considered “high pH” or overly alkaline. This compromises both swimmer comfort and the pool’s operational safety, making it necessary to correct the imbalance quickly.
Health Risks of High Pool pH
The most immediate concern for swimmers in high pH water is the physical discomfort it causes. Water with an elevated pH, especially above 7.8, strips the skin and hair of their natural protective oils. This leads to dryness and irritation, leaving the skin feeling itchy or tight after swimming, sometimes resulting in a rash or sensitivity.
The eyes are particularly sensitive to alkaline water. High pH levels are a primary cause of the redness, burning, and dryness often associated with pool swimming. The water’s pH is far from the natural pH of human tears, causing a reaction as the body attempts to neutralize the alkaline substance. Prolonged exposure increases the likelihood of these discomforts.
High pH can also indirectly contribute to respiratory irritation, especially in enclosed spaces like indoor pools. When the pH is too high, chlorine is less effective, leading to a buildup of volatile compounds called chloramines. These chloramines are responsible for the strong, unpleasant “chlorine smell” and can irritate the lungs, throat, and nasal passages, sometimes exacerbating conditions like asthma. Reduced sanitation due to high pH also presents a safety concern from potential pathogen growth.
How High pH Affects Water Quality and Equipment
High pH fundamentally compromises a pool’s ability to remain clean and safe due to chlorine inactivation. Chlorine’s sanitizing power comes primarily from hypochlorous acid (HOCl), the active, fast-acting form of the disinfectant. As the water’s pH rises, more HOCl is converted into the less effective hypochlorite ion (OCl⁻). This drastically reduces the chlorine’s ability to kill bacteria and algae.
For instance, at a pH of 7.5, chlorine is about 50% effective, but at a pH of 8.0, its effectiveness drops significantly to only about 20%. This reduction means that harmful microorganisms can survive and multiply, creating a major water safety issue. The high alkalinity also causes minerals, particularly calcium, to precipitate out of the water, leading to cloudy pool water.
This mineral precipitation results in scaling, which appears as rough, white or gray deposits on pool surfaces and equipment. Scale formation not only makes the pool look unappealing but also clogs filters, reducing their efficiency and straining the pump. Over time, this buildup decreases the lifespan of heaters, pipes, and other mechanical components, leading to increased maintenance costs and reduced circulation.
Steps for Correcting Elevated pH
Correcting an elevated pH level begins with accurate water chemistry testing, using a reliable test kit or strips. Once a high pH reading above 7.8 is confirmed, the corrective action involves adding an acid-based chemical, often called a pH decreaser. The two most common chemicals used are muriatic acid (a strong liquid acid) and sodium bisulfate (a granular or “dry acid”).
Pool operators must handle these chemicals with caution, wearing protective gear such as gloves and goggles, as both are corrosive. The acid should be added slowly according to the manufacturer’s instructions. This often involves diluting it in water before pouring it into the pool, typically near the deep end. Proper circulation is needed to ensure the chemical disperses evenly.
It is important to adjust the pH level gradually, rather than attempting a large correction all at once, as overshooting the target can lead to new problems. After the initial dose, the pool water should circulate for several hours before retesting the pH level. This process of testing, adding a small amount of acid, and retesting should be repeated until the pH falls back into the desired 7.4 to 7.6 range.