DPD No.3 is used in the DPD method for the determination of chlorine and for the correct dosing of the water care product. DPD No.3 is used to determine the level of total chlorine. The DPD No.3 tablet is added to the water sample after the free chlorine has already been determined with DPD No. 1. The tablet is crushed with the stirring rod and mixed by swirling. Now the value can be measured. If the value of free chlorine is subtracted from this value, the content of combined chlorine is present. With DPD No. 3, bromine, ozone and monochloramine-dichloramine can also be determined.