Picked up more AQ500 this morning, paid $36 per bag not including tax. So I've gone from being told to expect a $10 per bag price increase in the beginning, to paying $38.50 a bag on my initial order, and now $36.
I think I'll quit trying to apply any sense of logic to Purina's pricing structure, and simply enjoy the feed at a cheaper price.
Thanks Purina! My fish and I appreciate your efforts.