HF Scientific 9941 Total Chlorine Micro Check Test Strips, 0-1 and 1-10 ppm Range

Instructions say to use the aperture to get color match; but the fabric pad that contains the reagent covers the aperture. Plus, the color of the pad and the colors on the bottle don't seem to match very well under 2700k light. If you place the aperture over the bottle - they really don't match. Poorly enough that I was unable to determine a match on two strips.The strip has only ONE reagent pad. It is used for both 1ppm and 10ppm testing. The difference is how long you immerse the pad in water. 5 seconds for 10ppm, 10 seconds for 1ppm. Then you wait 30 seconds as the reagent develops, you have 15 seconds to do the color match -- all while the color is changing fairly rapidly. And under 2700k light, nothing matches.Also, the reagent pads change color as you watch them develop, that's expected, but they never stop changing color. You have only a few seconds to "read" a result, and if you miss the time window you wasted a strip. And the difference in color during the 15 second match window is like chasing rainbows.The really lousy part of the 'design' is that if you must match colors with the fabric over the reference colors, then you can't use match strips holding the test strip beside the line of colors - everything is too light. And if you touch the bottle with the strip then the strip wets the bottle and you have only a part of the small aperture one color, with a ring of different color around it, and a third color outside that where there is no aperture.Just tried again under daylight conditions. Same. Can't find a color match - or anything that is closer than somewhere between less than nothing to midway up the chart.Unusable for me. Returning the remaining strips since they appear defective to me. It looks to me like they use very subtle hues to differentiate readings. Anyone with any color vision deficiency should avoid. Even then, the swings in color during the reading period makes them unusable for most.

Product is as advertised, good price range, and delivered quickly.