Plants Photosynthesis Process

I was interested by the question on "Rate of O2 generation vs CO2 consumption on plants". Did some search on the internet, unfortunately unable to find the answer but I found more interesting info on photosynthesis. The O2 production in photosynthesis does not require CO2, well at least not directly.

This is different than what we learn in high school. We learn the simplified form.
6 CO2(g) + 12 H2O(l) + photons → C6H12O6(aq) + 6 O2(g) + 6 H2O(l)

Photosynthesis occur in 2 stages, light dependent reaction (Light reactions) and light independent reaction (Calvin-Benson Cycle/Dark reaction). Infact O2 is procuded during light reactions without CO2 as its ingredient.

Light dependent reaction in green plants:
2 H2O + 2 NADP+ + 2 ADP + 2 Pi + light → 2 NADPH + 2 H+ + 2 ATP + O2

Then I question myself, why in my tank plants need CO2 injection before you can see O2 bubble being produced? From the equation above, what I need is light and water to produce O2.

It is more complex than that. The light reaction in plants require NADP+, ADP and Pi. NADP+, ADP and Pi are produced during the Calvin-Benson Cycle. Calvin-Benson Cycle consumes NADPH from lightreaction, ATP and CO2. Without CO2, no Calvin Cycle. Without the Calvin cycle, There will be no NADP+ and plant won't be able to keep the light reaction going. Now you can see the relation.

Light independent reaction (Dark reaction/Carbon fixation/Carbon reduction):
3 CO2 + 9 ATP + 6 NADPH + 6 H+ → C3H6O3-phosphate + 9 ADP + 8 Pi + 6 NADP+ + 3 H2O

Full article can be read from Wiki