Re: Understanding CO2 fertilization

OK, I understand the carbon cycle, in general.  And I understand that
green plants, during photosynthesis, bring down the CO2 levels in a tank,
and that the CO2 levels come back up during the night, when the green
plants continue to respire but cease to photosynthesize.  My question is
this:  what is the fluctuation in CO2 levels relative to the natural level
of CO2 in well-aerated freshwater?

That is, does the CO2 level get depressed during daylight hours, and
replenished at night, or does the CO2 get super-saturated at night from
fish/plant respiration, and get consumed by the plants in the day?  Or

The point of my question is to understand the effect of CO2 fertilization:
is the goal of fertilization to maintain the daylight CO2 levels up to
their natural state (that is, to avoid depression), or is the point to
keep the water super-saturated with CO2 at all times?  Will heavy
aerations in an external filter keep the CO2 levels from getting
depressed, or is CO2 fertilization the only method that's really

                                       --  Edziu