Test strips are often bad, depending on the test and the manufacturer of the strip and its age, etc. The Taylor drop-based tests are far better and for chlorine nothing beats the FAS-DPD test which does not bleach out (you just add more powder if you see a flash of pink), can measure up to 50 ppm, and can measure with an accurate of 0.2 ppm if you use a 25 ml sample size. The complete kit is the
Taylor K-2006, but you can get just the FAS-DPD kit, the
Taylor K-1515-A or the equivalent kit from
tftestkits.net that has more volume of reagents so is more economical.