I switched our pool over to the BBB method about two weeks ago. I purchased a Basic OTO kit and a Taylor K-2006 kit for testing. I have been very regular about testing and the chroline level has been very consistent (around 11 every night). Over the weekend I picked up a SpeedStir kit. I used the SpeedStir for the first time last night, and the chlorine level indicated was 8.5 (17 drops using 0.5 ppm per drop). I repeated the test without the SpeedStir (by manually swirling) and the level indicated was 11 (22 drops). I tried again and saw the same results. I then used the OTO test and the yellow was darker than the yellow for the 5-10 range (indicating the chlorine was above 10).

The delta between these tests seems too high to be accounted for in the margin of error. Does the SpeedStir somehow skew the measurement of the FAS-DPD test? I found another thread where chem geek indicated that the amount of swirling can lower the result slightly (http://www.poolforum.com/pf2/showthr...?6427-Fas-dpd&), so I'm not sure if the SpeedStir "over-swirls" the test.

Thanks!