Oxidation reduction is a process by which a molecule or ion loses or gains electrons. This occurs most readily in water treatment and in pool and spa maintenance where an oxidizer, such as chlorine, is added to the water to destroy contaminants. The higher the ORP value, the greater the sanitizing power of your water. HI98201 is ideal for swimming pools and spas and can provide a valuable indication of water quality. This tester utilizes a platinum electrode and Hanna unique renewable cloth junction, that can be pulled out when clogging occurs, reactivating the referenceand restoring the electrode.