The Chlorine DPD #1 Instrument Grade TesTabs® Tablets are specifically designed for measuring free chlorine levels in pool and spa water using electronic colorimeters and photometers. The #1 instrument grade indicates the specific formulation of the DPD reagent, providing highly accurate measurements in free chlorine detection. This formulation enhances measurement accuracy and offers consistent performance, making it easy to achieve quick and clear results with compatible devices. Pack contains 50 tablets.