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The carbonate-bicarbonate buffer system is used in pools and spas to maintain the pH in a consistent range. For increasing alkalinity, sodium bicarbonate, NaHCO3 , (BioGuard Balance Pak 100) is added to the pool to introduce the bicarbonate ion.   

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The alkalinity is increased with the addition of the bicarbonate ion because this ion provides sites to allow association with hydrogen ions, the acid component of water. This buffering capacity actually protects against increases or decreases in pH, as this ion can accept or release hydrogen ions, depending upon the concentrations of each the ions present.


Increases in pH are accomplished by additions of sodium carbonate, Na2CO3, (BioGuard Balance Pak 200), providing the carbonate ion.


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The carbonate ion has three sites available for association with hydrogen ions. As the hydrogen ion concentration decreases with the addition of carbonate, the pH increases. Sodium sesquicarbonate is a 50/50 mixture of sodium carbonate and sodium bicarbonate. This is not a mixture created by mixing equal quantities of the two compounds. Sodium sesquicarbonate is a reaction product which is created in the reactor at the 50/50 relationship. This product will introduce both the carbonate and bicarbonate ions when dissolved in water, producing increases in both pH and alkalinity. Other ions are involved in alkalinity, including phosphates, silicates, borates and hydroxides.


The above information is supplied by Bio-Lab and represents its best interpretation of available technical information at the time of preparation. The sole purpose is to supply factual information to Bio-Lab customers. It is not to be taken out of context nor used as support for any other claim not made herein.