The HI93703-53 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 interfere with measuring the sample. To eliminate Cl2 interference add to the 10 mL unreacted sample, 1 drop of the HI93703-53 Chlorine Remover, for each 2 mg/L of chlorine.These reagents are optional and should only be used when chlorine is present in the sample.