Nice writeup Tom. I must admit, I've often wondered about the gas bubble theory also. I get intense pearling after a water change, especially from some Riccia remants (annoying pest) that I am still cleaning up after experimenting with it as a foreground plant. I don't take water straight from the tap. My water is taken from a 30 gallon storage container for natural dechloration (our supply only uses chlorine, and very little of it). Our local water is mostly from rainwater runoff and snowmelt, so it's very low in TDS, so there is not much in the way of nutrients added to the water. I see the same thing that you have described in experiment 1. I get the most intense pearling for about 6 - 8 hours after the change.

Prior to getting pressurized CO2, I used to only have pearling after a water change (I had DIY CO2). Now, with pressurized, and using your misting method (diffuser arranged under the outlet of my canister), I get significant pearling after 2 - 3 hours of lighting, every day, but never as good as after the water change.