This Total Alkalinity Standard Reagent measures levels of alkalinity. Total alkalinity levels should be maintained between 60-120 ppm, and an incorrect balance can lead to corrosion and damage to pools. 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.