I have an idea…
You know how carbon dioxide is a Lewis acid, so maybe that is the kind of reaction you are experiencing?
If you bubble air through tap water, there will be more CO2 available in the air than dissolved in the water, some will dissolve, and form carbonic acid, thereby lowering the pH.
If you bubble air through water with a lot of carbonic acid already in it, some of it will dissolve in the air bubbles and leave the solution, thereby raising the pH.
It has been close to two decades since my last chemistry class, so I cannot say with any certainty whether this will apply to whatever you have in that solution, but that principle might.
Also, bubbling air through water offers a much smaller total area of surface contact than misting water through air, so the reactions, if in fact occurring, would be much faster and more complete IMHO