David....I am observing the same thing, a major drop, then a continued drop, after my first two rounds of OA treatment. Also, I have not had any powdery residue in my copper pipe setup after 60-90 seconds of low propane heat. First you can hear it bubble in the pipe, then you keep heating and it vaporizes. There is some minor residue around the hole where I insert it into the hive. You may want to try copper sometime because it heats so quickly and easily. You can pretty much gauge its temp by appearance after you have done it a few times.