There may be a bad batch of AquaChek strips. I got two bottles this season, same lot number, and I have checked at least two or three strips from each bottle and none of the strips "darken" across the top band as my strips (different lot number) did from last year. I can let them sit for over an hour and they still don't darken at all although I believe they are accurate in their readings because they match the readings that last year's bottle is still giving me. My new Taylor test kit gives me the same 3200 PPM as the all of the strips do, regardless of which bottle they come from.
Lot number 9026 dated 2010/12, no darkening whatsoever across the top yellow band.