Can alkalinity or ANC be negative?
Yes. Alkalinity and ANC are just a measure of the deficiency of H+ ions relative to a solution of carbon dioxide in water. A negative alkalinity or ANC simply reflects the presence of some amount of mineral acidity, or an abundance of H+ ions relative to a solution of carbon dioxide in water. Alkalinity and ANC may be positive, zero, or negative. It is instructive to note that concentrations of hydroxide, carbonate, and bicarbonate ions, unlike alkalinity and ANC, cannot be negative. Of the various titration analysis methods available in the Alkalinity Calculator, only the Gran function plot method is able to detect and report negative values of alkalinity or ANC.
