The 2000 Series Comparator is designed for the kind of comprehensive, routine testing performed by service technicians, commercial public pool operators, and health department inspectors. It tests for low range bromine and chlorine, DPD and pH 7.0-8.0. Easy to follow instructions allow for hassle free testing. Taylor formulates its reagents to remain effective for at least one year, with only very few exceptions (molybdenum indicator in liquid form is one; after four months old it should be tested against a standard periodically). As a general precaution, replace all reagents more than one year old, or at the beginning of a new testing season.