A special mixture of indicator dyes assumes a characteristic colour for every pH value within the range of the kit. The favourable ratio between sample volume and amount of indicator minimises the indicator error (acid-base-error). This allows reliable pH measurements in weakly buffered solutions as well. High contents of neutral salts and colloids as well as organic solvent concentrations above 10 % can cause wrong results.

The pH value indicates whether a water reacts acidic, alkaline or neutral. It is determined by the concentration of hydrogen ions. All biological processes in water are tied to specific pH ranges. For municipal and industrial applications, too, the control of specific pH limits is important since e. g. the efficiency of sewage plants or the corrosive action of tap water on the pipes depend in the pH value. Contrary to pH indicator papers VISOCOLOR® pH test kits can also be used to determine accurate pH values in unbuffered sample solutions.