Q-CL501 Portable Colorimeter for Free Chlorine, Chlorine Dioxide ( 5-para) is a professional water test kit which contains all the accessories you need to use for water analysis both in laboratory and field test.It is the first domestic and foreign testing instrument that can simultaneously detect free chlorine, total chlorine, combined chlorine, chlorine dioxide, and chlorite. It based on EPA methods, and each of them has calibrated standard curve respectively,just simply add the reagents you need to test your water and customize your water test kit.