Phenol red is used for pH measurement. The tablet produces characteristic colour changes when dissolved in the water sample. The pH value is important for the disinfectant effect of water care products. It can also cause corrosion or precipitation and thus damage materials. Lovibond tablets contain thiosulfate to compensate for the disturbing influence of chlorine on the measurement in bath water analyses. In addition, the carbonate content, temperature and buffer capacity of the water sample can affect the measurement and should therefore also be observed. This tablet is designed for use in photometers.