@Larry3215, my answers were given by what seemed logical. And you are right about the stone. Yes it would be adjusting the pH even without the air pump, but would probably taken longer to do it. Clearly, since I have never grown in anything other than R.O. water, my experiences are not valid in this context. !!!!!!
It just seemed logical that for pH to change in a captured water system, something needs to be added or subtracted from the water. The fact that your experiment works out that way is, to my way of thinking, impossible. It just goes to illustrate that things often defy logic, like a bumble bee flying. According to science. a bumble bee can't possibly fly due to its weight to wing ratio and the total lack of aerodynamics in its shape.
My water is so bad, I have never even consider drinking it, let alone feed it to my plants. I'd never put a bunch of unknown minerals/chemicals at unknown quantities into my plant nutes.
BTW, I hope you and @legalcanada realize that after your explanations, I agreed that they were possible solutions. I just thought my answer was the correct one.
Thanks for the definition, but it was unnecessary. I've been using a pH meter since 2002 when I started growing.
Edit; made additional comment