Total Alkalinity (TA) measures the concentration of alkaline substances, primarily bicarbonates, in pool water. TA provides resistance against sudden changes to the pH level when acids or bases are introduced. When pool owners ask if it is safe to swim with low alkalinity, the immediate answer is that it is not typically an acute health hazard. However, maintaining TA is important to water chemistry, and ignoring low levels will quickly lead to conditions that make swimming uncomfortable and damage pool infrastructure. Therefore, while a brief dip might not be dangerous, swimming is highly discouraged until the water chemistry is balanced.
Swimming Safety and Comfort
Low TA causes the pH to become unstable and often drop, which results in highly acidic water, the primary source of swimmer discomfort. The natural pH of the human eye is around 7.4, and swimming in water significantly below this level can lead to redness, burning, and irritation. Skin may also experience dryness or itching because the acidic environment strips away natural oils, disrupting the skin’s moisture barrier.
When the water’s pH drops too low, the pool’s primary sanitizer, chlorine, becomes less stable and can dissipate quickly. While low alkalinity itself is not a direct threat, the resulting poor water balance compromises the water’s sanitation efficiency. Pathogens are not killed effectively, increasing the potential for recreational water illnesses, making the pool unsafe for prolonged use.
How Low Alkalinity Affects Pool Stability
When TA is low, the buffering capacity is lost, leading to what is commonly called “pH bounce.” Inputs like rainwater, swimmer waste, or chemical additions cause the pH to fluctuate rapidly and dramatically, making consistent water management nearly impossible.
An unstable pH level directly impairs the effectiveness of chlorine, the most common pool sanitizer. Chlorine exists in the water in two main forms: hypochlorous acid (HOCl) and hypochlorite ion (OCl-). The concentration of the more potent form, hypochlorous acid, is highest when the pH is maintained between 7.2 and 7.6. When low TA causes the pH to drop outside this optimal range, the chlorine is either rendered inefficient or consumed too quickly.
Low alkalinity results in a sustained low pH, which makes the pool water corrosive. This acidic water attacks metal components within the pool system. Items like heater elements, pump seals, and metal ladders can experience accelerated degradation, leading to costly premature replacements.
The corrosive nature of low-alkalinity water also affects pool surfaces. Plaster, grout, and concrete surfaces can experience etching, where the acidic water dissolves the calcium compounds from the surface. This etching creates rough, abrasive textures and can also lead to staining as dissolved metals precipitate onto the newly exposed, porous surfaces.
Correcting Low Alkalinity Levels
The first step in addressing low alkalinity is accurately measuring the current level using a reliable liquid test kit or test strip. The accepted range for Total Alkalinity in swimming pools is typically between 80 and 120 parts per million (ppm). A level below 80 ppm indicates a need for immediate correction to restore the water’s buffering capacity.
The standard chemical used to increase TA is sodium bicarbonate, often marketed simply as “alkalinity increaser.” This chemical is preferred because it raises the alkalinity with only a minor, gradual effect on the pH level, making the overall water chemistry adjustment easier to manage.
The calculated amount of sodium bicarbonate should be dissolved in a bucket of water before being added slowly to the pool, typically near a return jet to ensure rapid circulation. After the chemical has been distributed and the water has circulated for several hours, the water should be retested. This retesting confirms the TA is within the target 80 to 120 ppm range, successfully stabilizing the water’s buffering capacity.