Detect higher levels of peroxide where used as a disinfectant. Peroxide Test Strip, 400ppm The Peroxide test strip is calibrated at 0, 100, 200, and 400ppm, and gives results in just seconds. This test strip can be used to test pools and hot tubs where peroxides, rather than chlorine, are used to sanitize. Recommended peroxide levels vary, therefore, the test strip can be used to test the concentrations users prefer. Instructions: 1. Remove one test strip from the vial. Do not touch the test pad with your fingers. 2. Dip the test strip into the solution being tested for 1 second. 3. Remove and shake off any excess liquid. 4. Compare the test pad to the color chart after 30 seconds. NOTE: If this test strip is used in very high concentrations of Peroxide (above 2000ppm or 0.2%), the test strip will not turn purple. Instead, it will turn an off-white with a hint of green.