I think the belief that pearling indicates O2 saturation of the water is incorrect. Pearling only indicates that at the leaf surface, there are places where more O2 is released than can quickly be dissolved into the water, so a gas bubble forms. O2 doesn't dissolve easily into water compared to how easily CO2 dissolves, so the way water and O2 react is different from how water and CO2 react.

Also, we never ever come anywhere near to saturation of the water with CO2. Water can dissolve in the neighborhood of 1000 ppm of CO2 - seltzer water, for example. Long before our tanks would reach that level even the plants would be suffering.

I'm not a biologist by any stretch of imagination. But, I think excessive CO2 primarily bothers fish because they can't get rid of the CO2 in their blood, just as it does humans. I don't understand how it affects their ability to use O2, otherwise. I think Tom has explained this before, and as I recall I am incorect about the reason high CO2 levels bother fish - but being wrong occasionally never has bothered me too much!