Maintaining balanced water chemistry requires attention to two primary parameters: pH and Total Alkalinity (TA). These factors work in tandem, and imbalance often requires adding an acid to restore equilibrium. This article addresses whether the dry acid, sodium bisulfate, is effective for reducing Total Alkalinity and explains its chemical action.
Understanding Total Alkalinity
Total Alkalinity (TA) measures the concentration of alkaline substances in the water, primarily carbonate and bicarbonate ions. This concentration acts as a buffer, providing the water’s resistance to drastic changes in pH level. For most recreational water settings, the ideal TA range is maintained between 80 and 120 parts per million (ppm).
If the TA level falls below this range, the buffering capacity is lost, leading to rapid and unpredictable pH fluctuations known as “pH bounce.” When TA rises too high, typically above 120 ppm, the water becomes “over-buffered,” making it difficult to adjust the pH down (often called “pH lock”). High TA levels can also contribute to cloudy water and the formation of scale deposits on equipment.
Sodium Bisulfate and the Lowering Mechanism
Sodium bisulfate lowers alkalinity because it is a powdered acid specifically designed for this purpose. Sodium bisulfate (\(\text{NaHSO}_4\)) is an acidic salt that serves as a granular alternative to liquid acids like muriatic acid. When dissolved in water, sodium bisulfate dissociates and releases hydrogen ions (\(\text{H}^+\)) into the solution.
This release of hydrogen ions is the core of the lowering mechanism. These ions chemically neutralize the existing bicarbonate and carbonate ions that constitute Total Alkalinity. The \(\text{H}^+\) ions react with these species, converting them into carbonic acid (\(\text{H}_2\text{CO}_3\)). By consuming these buffering agents, the chemical reduces the water’s capacity to resist pH changes, thereby lowering the measured TA level.
The reduction of TA is always followed by a corresponding drop in pH, which is expected when adding any acid to water. The mechanism prioritizes consuming the alkaline buffers first. This is why sodium bisulfate is often used to correct high TA before fine-tuning the pH. This process efficiently brings over-buffered water back into the ideal range.
Practical Application and Dosage
To effectively use sodium bisulfate, pool owners must calculate the precise dosage required based on the pool’s volume and the desired parts-per-million change. A common guideline for granular sodium bisulfate is: (Volume in gallons \(\div\) 47,058) \(\times\) desired ppm change = pounds of product. It is recommended to use less than the calculated amount for the first application to avoid overcorrection.
The dry acid should first be dissolved in a bucket of water before being added to the pool. This prevents the concentrated chemical from settling and potentially damaging the pool surface. The diluted solution should then be poured slowly into the deep end while the circulation pump is running to ensure even distribution. Allowing the water to circulate for at least four to six hours is necessary for the chemical reaction to complete and the water to mix thoroughly.
Safety is paramount when handling this chemical, so users should wear appropriate personal protective equipment, including gloves and eye protection. After the initial circulation period, the water must be retested to verify the new TA level before considering further adjustments. Making small, incremental changes and retesting is the most reliable method for safely lowering TA and achieving the ideal water balance.