"François Arsenault" wrote

what happens to a plant if one stops using a CO2
injector after using one for some time? Will the plant do especially badly,
suffering from CO2 withdrawal, or will it simply go back to the growth level
it previously had before CO2 was used? In other words, does the extra CO2
induce physiological changes in the plant other than making it healthier for
the time CO2 is added?

I can't speak to physiological changes, but I've never seen any
negative impact aside from slower growth result from less CO2. At
concentrations under 20ppm, CO2 is like a speed control: lower the
bubble rate, plant growth slows down. Increase it, plant growth
accelerates.