chem_geek: I watched the Taylor video, and I would say that my original swirling (not the aggressive style) was about the same as in the video. One difference between my swirling and the video is that I am not yet able to swirl and drop at the same time (my coordination isn't there yet). I would add one drop, then swirl, then another drop, then swirl, etc. I noticed in the video that the presenter was manually swirling the entire time while adding drops (which is similar in behavior to the Speedstir). When I use the aggressive style swirling, the water keeps moving between swirls while adding the next drop.

Last night, I performed test #10 from PoolDoc's list. This involved using the Speedstir to mix the DPD powder in each of two samples, and using the Speedstir while dropping one sample and manually swirling the other sample (with my original style swirling). The Speedstir took 16 drops and the manual took 20 drops. I also tried chem_geek's suggestion of agitating the water before adding any reagents. I ran the Speedstir on the water sample for about two minutes before adding the DPD powder. I mixed the DPD manually and swirled manually after each drop. This took 20 drops. At least with this test, it appears as if the difference in results is due to the stirring method while adding drops. I'll perform tests #12 and #14 from the PoolDoc's list, but I need to order more reagent.