Industrial Test Systems WaterWorks 480024 Free Chlorine Test Strip, Ultra High Range, 31 Seconds Test Time, 0-750ppm Range (Bottle of 50) Test strips measure the amount of free chlorine in food and beverage processing and other applications 0, 25, 50, 100, 200, 300, 400, 500, and 750 ppm (mg/L) detection levels 31 second test time Resists interference from monochloramines 50 test strips