Co2 is only useful to plants when there is light at night the plants use oxygen just like the fish do I open the bottle with the "brew" in it at night when not introducing the CO@ into the tank the fermentation will continue 24/7 but the gas will just fo into the atmosphere and not the tank when you disconnect.
I agree that for a large tank you would probably need multiple bottles of "brew" set up you may want to invest in a CO2 tank and regulator
to get the most of the CO@ be sure to intorduce the CO2 into the suction of your filter it will dissolve better becaus of the increased contact time. GOOD LUCK