About the gas escaping from the plants, i.e. pearling, immediately during the water change, that's probably due to the lower gas concentration in the tap water. This forces the gas to be expelled from inside the plants where the concentration is high. I was able to prevent this from occurring by oxygenating the water with an air stone over night. So aside from the pH drop, oxygen was added to the water. No plants pearled during the water change. I infer that not only is my tap water extremely low in CO2, it is also very low in dissolved O2. Without an O2 meter, I can only infer that this is the case based on these observations.