Description This test strip provides fast and reliable monitoring of chlorine dioxide levels, including residuals. Detects levels from 0-500ppm in increments of 0, 10, 25, 50, 100, 250, and 500. Using a cup-size sample, immerse the test strip for 2 seconds. Remove the strip with the pad face up. Do not shake off excess water. With pad still facing up, wait 10 seconds and read the strip against the colour chart. Discard test strip after 30 seconds.