Maintaining a swimming pool requires chemical balance for effective sanitization and water stability. Chlorine is the most common sanitizer, dissolving in water to kill pathogens. Total Alkalinity (TA) is a separate measure that determines the water’s resistance to pH change, playing a major role in pool stability. The effect of chlorine on alkalinity is not uniform; it depends entirely on the specific chemical formulation used. Proper water balance protects pool surfaces and equipment while ensuring chlorine works effectively.
Understanding Total Alkalinity
Total Alkalinity is a measurement of the concentration of alkaline substances dissolved in the pool water, primarily bicarbonates and carbonates. This measurement is distinct from pH, which gauges how acidic or basic the water is at any given moment. TA’s main function is to act as a “buffer,” absorbing acid and base additions to stabilize the pH level.
If the Total Alkalinity is too low (below 80 parts per million (ppm)), the water loses its buffering capacity, leading to rapid and extreme shifts in pH, known as “pH bounce.” If the TA is too high (above 120 ppm), the water is over-buffered, making it difficult to adjust the pH. High TA can also contribute to cloudy water and scale formation. The recommended range for Total Alkalinity is 80 to 120 ppm.
The Chemical Impact of Different Chlorine Types
The answer to whether chlorine increases alkalinity is complex, as it varies depending on which of the three main types of chlorine is added to the pool. Each form introduces different byproducts that either raise or lower both the pH and the Total Alkalinity.
Cal Hypo (Calcium Hypochlorite)
Calcium hypochlorite is a non-stabilized form of chlorine that is highly alkaline, meaning it has a high pH when dissolved. When added to water, Cal Hypo increases both the pH and the Total Alkalinity of the pool. This effect is a chemical consequence of the product’s composition, which also adds calcium to the water. Pool owners must frequently monitor the pH when using Cal Hypo and may need to add an acid, like muriatic acid, to counteract the rising alkalinity and pH.
Liquid Chlorine (Sodium Hypochlorite)
Liquid chlorine, or sodium hypochlorite, is also a highly alkaline product with a very high pH level. When initially introduced, it raises the pool’s pH significantly, but its effect on Total Alkalinity is usually negligible or only slightly increasing. The chlorine sanitizing process, however, generates a small amount of acid as a byproduct, which can nearly neutralize the initial pH increase over time. This temporary spike in pH means that pools using liquid chlorine often require regular, small additions of acid to maintain the pH within the ideal range.
Stabilized Chlorine (Dichlor/Trichlor)
Stabilized chlorine products, such as Dichlor and Trichlor, have the opposite effect on water chemistry. Trichlor is highly acidic, with a pH of around 2.7 to 3.3, and its use consistently lowers both the pH and the Total Alkalinity. This is because both Dichlor and Trichlor release cyanuric acid (CYA) as they dissolve, which is acidic and consumes a portion of the water’s existing alkalinity. Dichlor is less acidic than Trichlor, but it still reduces both pH and TA over time, requiring pool owners to add an alkalinity increaser to prevent the water from becoming corrosive.
The Relationship Between Alkalinity and pH
Total Alkalinity and pH are interdependent components of pool chemistry, with TA acting as the primary control mechanism for pH stability. The buffering capacity of TA allows the water to absorb ions released by acids or bases without experiencing drastic changes in pH. This protective mechanism prevents the pH from shifting wildly in response to chemical additions, rain, or swimmer load.
When the TA level is too low, the buffer cannot absorb minor additions, causing the pH to rapidly swing up or down, known as “pH bounce.” This instability makes it difficult to maintain the optimal pH range of 7.4 to 7.6, which is necessary for effective chlorine sanitization. Therefore, pool maintenance protocol dictates that Total Alkalinity must be adjusted first. Once the TA is within the ideal 80 to 120 ppm range, the pH can be fine-tuned.