The fallacy of using
sodium bicarbonate
Oddly, one of the most frequently recommended
treatments for high pH—sodium
bicarbonate (also called bicarbonate
of soda or baking soda)—is the least
effective. Sodium bicarbonate reduces
high pH in water because it neutralizes
either acids or bases. (Compounds with
this property are called amphoteric.)
Sodium bicarbonate is, however, a weak
acid and large amounts must be added
to significantly reduce pH, especially in
waters with high total alkalinities (Table
1). For example, if water has a total
alkalinity of 200 mg/L as CaCO3 and
a pH of 10.0, then adding 100 mg/L of
sodium bicarbonate will reduce the pH
to only about 9.9. At this rate, a 2-acre
pond that is 4 feet deep would need
about 270 pounds of chemical per acrefoot,
or a little more than 2,000 pounds.
The same amount of sodium bicarbonate
(100 mg/L) added to water with an
initial alkalinity of 50 ppm as calcium
carbonate will reduce pH to about 9.6.