The HI93703-52 are high quality reagents that are pre-measured, allowing for users to achieve fast and accurate colorimetric measurements. These reagents are used to remove the chlorine interference which would also react with DPD causing a pink tint in the sample. By simply adding the reagent to the sample, a reaction will take place to remove the interference. The HI93757-0 reagent for ozone is then added to the sample and the colorimetric analysis then performed. These reagents are optional and should only be used when chlorine is present in the sample.