Baking soda, or sodium bicarbonate, is often mistakenly believed to be a universal water treatment agent. However, it does not lower alkalinity. Instead, it is used specifically to raise the water’s total alkalinity.
Understanding Total Alkalinity and pH
To understand how baking soda affects water, it is important to first distinguish between Total Alkalinity (TA) and pH. Total Alkalinity is a measure of the water’s capacity to resist changes in pH, essentially acting as a chemical buffer. It is measured in parts per million (ppm) and primarily represents the concentration of dissolved alkaline substances like bicarbonates, carbonates, and hydroxides in the water.
The pH, on the other hand, is a measure of the water’s acidity or basicity on a logarithmic scale from 0 to 14. A pH below 7 is acidic, while a pH above 7 is basic. Total Alkalinity stabilizes the pH, preventing fluctuations due to external factors like rain or chemical additions.
The Chemical Mechanism of Baking Soda
Baking soda’s chemical formula is NaHCO3, or sodium bicarbonate. When dissolved in water, the compound undergoes dissociation, separating into a sodium ion (Na+) and a bicarbonate ion (HCO3-).
The bicarbonate ion is the primary component of the water’s buffering system. By introducing more of these ions into the water, you are directly reinforcing the buffer, which causes the Total Alkalinity to increase. This action makes sodium bicarbonate an ideal chemical for adjusting alkalinity in a controlled manner.
Sodium bicarbonate has a relatively mild basicity, registering a pH of approximately 8.3 when dissolved. This allows users to raise total alkalinity without causing a severe spike in the overall pH level, unlike stronger bases such as sodium carbonate (soda ash). The gentle effect on pH while providing a significant boost to the buffering capacity is why baking soda is the ingredient in many commercial “alkalinity increaser” products. Adding about 1.5 pounds of baking soda per 10,000 gallons of water typically raises the Total Alkalinity by 10 ppm.
Using Acid to Reduce Alkalinity
Since baking soda is used to increase alkalinity, the correct method for lowering alkalinity involves the use of an acidic compound. An acid works by consuming the very bicarbonate ions that make up the water’s buffer system. This chemical reaction effectively reduces the concentration of alkaline material in the water, thereby lowering the Total Alkalinity.
The two most common chemicals used for this purpose are Muriatic Acid and Sodium Bisulfate. Muriatic acid is a liquid form of hydrochloric acid, a highly potent and corrosive chemical. When added to water, the acid reacts with bicarbonate ions, converting them into carbonic acid, which then releases carbon dioxide gas.
Sodium Bisulfate, often sold as “dry acid” or “pH decreaser,” is a granular alternative that achieves the same result. While it is a strong acid, it is considered safer and less corrosive to handle than liquid muriatic acid. Due to the corrosive nature of these products, safety precautions are important. These include wearing protective gloves and goggles, ensuring adequate ventilation, and always adding the acid slowly to water, never the reverse.