Quick update of some things that happened off thread. First,
@Archiweedies had a thought that maybe the chloramine in my water was messing with the effectiveness of the Vulx. So I ran that thought past the Vulx rep, and his response was that I should try chloramine-free water and see how that went.
Fair enough. According to wikipedia, ascorbic acid (Vitamin C) will neutralize chloramine. So I'll head to Trader Joe's and get a cheap bottle (I use the high-end Calcium Ascorbate from Freeda Vitamins).
I found on a beer-brewing website that recommended 1 mg ascorbic acid / Liter of water, or 3.78541 mg/gallon. Crush and weigh and mix in a bucket!
We'll see...