The 0-100ppm hydrogen peroxide test strip is used to determine residual H2O2 levels down to 1ppm. Peroxide test strips are a plastic strip with a reactive pad on one end. Dip the pad into the solution for 1 second. After 5 seconds compare the color of the pad to the color scale on the bottle. Test strips measure from 0 to 100 parts per million. Hot tubs are kept between 30 to 100 ppm hydrogen peroxide. We have also been advised by one of our customers that using a 5ppm hydrogen peroxide solution is becoming the preferred method for treating koi ponds.