Day 2: The Critical Role of pH and Alkalinity in Pool Water Balance
Maintaining proper pH and total alkalinity is essential to preserving water quality, ensuring swimmer comfort, and protecting the structural integrity of a gunite/plaster pool. These two parameters work together to stabilize your pool’s chemistry and form the foundation of effective water management.
This article explains the function of pH and total alkalinity, their recommended ranges, and how to adjust them correctly to prevent costly mistakes.
Understanding pH and Alkalinity
pH measures how acidic or basic the water is, on a scale from 0 to 14. For swimming pools, the ideal pH range is 7.4 to 7.6. This range closely matches the natural pH of the human eye and mucous membranes, minimizing irritation while also maximizing chlorine efficiency.
Total alkalinity (TA) refers to the concentration of alkaline substances in the water, which buffer the pH and prevent sudden fluctuations. The recommended range for total alkalinity in plaster pools is 80 to 120 parts per million (ppm).
Together, pH and alkalinity determine how stable and safe your pool water remains. If one or both are out of range, it can cause scaling, corrosion, ineffective sanitation, and surface damage.
Why Proper Balance Matters
Swimmer Comfort
Low pH can cause eye and skin irritation, while high pH often results in cloudy water and discomfort. Maintaining the ideal range helps ensure a pleasant experience for swimmers.
Surface Protection
Low pH and low alkalinity levels can cause etching and deterioration of plaster surfaces by making the water aggressive. Conversely, high pH and alkalinity can lead to calcium scaling, especially on tile lines, fittings, and equipment.
Sanitizer Efficiency
The performance of chlorine is significantly affected by pH. At a pH of 7.2, chlorine is roughly 60% active. At 8.0, its effectiveness drops to about 20%. Keeping pH in range is essential to maximize disinfection without using excessive amounts of chlorine.
How to Correct Imbalances Safely
Lowering pH and/or Alkalinity
- Use muriatic acid or sodium bisulfate.
- If both pH and alkalinity are high, acid will help reduce both.
- If only pH is high and alkalinity is acceptable, use aeration (e.g., water features, spa jets) after adding acid to lower pH while preserving TA.
Raising Alkalinity
- Add sodium bicarbonate (baking soda) to raise alkalinity with minimal effect on pH.
- Apply incrementally, retesting between doses to avoid overshooting the target.
Raising pH Without Raising Alkalinity
- Use soda ash (sodium carbonate) to raise both pH and alkalinity.
- To increase pH only, aerate the water instead of adding chemicals.
Note: Always retest water after chemical additions and avoid adding acid and base products simultaneously. Allow the pool time to circulate between adjustments.
Additional Considerations
Order of Adjustment
When both pH and alkalinity are off, adjust alkalinity first, then pH. This sequence prevents the need for repeated corrections.
Environmental Factors
Rain, evaporation, and fill water can all impact alkalinity and pH. For example, heavy rain can dilute alkalinity and cause pH swings. Regular testing is essential, especially after storms or major water additions.
LSI (Langelier Saturation Index)
pH and alkalinity directly affect your pool’s LSI, which measures whether your water is balanced, corrosive, or scale-forming. Even if pH and TA are within target ranges, your water may still be aggressive if other factors like calcium hardness or temperature are not accounted for.
Summary
Maintaining proper pH and total alkalinity is a non-negotiable part of responsible pool ownership. These two parameters influence water comfort, surface protection, and the effectiveness of chlorine. By testing frequently, making controlled adjustments, and understanding the role of each component, you can keep your pool water balanced and your plaster surface in optimal condition.
Coming up next: Day 3 – Shocking the Pool: When, Why, and How. We’ll explore how to safely and effectively oxidize your pool water using traditional chlorine and non-chlorine methods.