I'm assuming this query is coming from the new Alaska State Museum project that I've been a part of, so I'll answer based on what I know about your process.
To start with, is this a new problem? Have the mounts that were patinated previously shown the same sort of color changes? If so, when did you start noticing the change? If not, what has changed? Is it time for a new batch of patina? At the production rate of your project, you may want to renew it regularly as the specific chemicals will get used up or contaminated. Are there other possible sites of contamination such as the rinse water or the abrasives in the blast cabinet?
I'm also wondering if the baking soda advice was something from the manufacturer that was based on their science, or if it was something that somebody just thought might be helpful? I only ask as the patina solution you were using was purchased from Rockler, and is probably a re-labeling of a product from someone else. It would be good to see if you could find out the specific manufacturer and see if you can find your way to their tech support. In other manufacturers instructions, I've never seen anything needed but a thorough water rinse to stop the process.
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