I need to get your book! I'm still so green (n.p.i.) at all of this, & too busy w/too many other things to do all I want with the aquariums, but after only 3 years in now, keeping fish & wanting to do it right, plus being so admittedly ignorant, I'm glad we have your input available here. So glad! That you yourself continue to research & learn, & then share, is a testimony to your humility as an undeniable & admirable expert. Thank you for everything!!Second thoughts....
If Mysiak, mistergreen, and other observant hobbyists are getting better plant growth with added aeration, I propose--after some reference work--an explanation.
In stagnant water, heavy photosynthesis would deplete CO2. It would also fill area surrounding leaves with unwanted oxygen. (Excess oxygen can reduce photosynthetic efficiency in some plants up to 50%.)
Outdoor air contains 350-450 ppm CO2 and indoor air contains more, about 1,000 ppm before it reaches unhealthy levels for humans. So water in equilibrium with indoor air probably contains more than the standard 0.5 and 0.7 mg/l that I quoted, let's say 1.0 mg/l. Not much CO2 but some. (Mistergreen's 3-4 mg/l is a little more than I would predict but maybe possible for those who live in sealed houses, lots of inhabitants, and gas stoves?)
Plants in stagnant water with zero CO2 (depleted by heavy photosynthesis) would probably benefit from water-air mixing that would constantly bring them 1 mg/l air CO2 and quickly flush out the inhibitory oxygen. The associated water movement would decrease the leaf boundary layer speeding up both these beneficial processes.
Aquatic botanists and my book recommend moderate water movement, but I always thought that water-air mixing (e.g., bubbling and degassing) would be detrimental. However, I realize now that in some situations aeration actually could be beneficial.