The acid capacity - also referred to as KS4.3, alkalinity-M, total alkalinity or hydrogen carbonate acid - describes the concentration of hydrogen carbonate ions (HCO3 -) dissolved in water. It influences the pH value and thus also the effectiveness of disinfectants or water care products. However, the acid capacity can also lead to material damage such as corrosion.

The Alka-M photometer tablet is used in photometers and spectrophotometers. Simply add the tablet to the water sample, crush it with the stirring rod, wait for the colour change and analyse it with the measuring device.