Well, yeah, If you tank is small then that's fine, but what if your tank is 400 gallons?
No mate please have another re-read of post #12. Excel=CO2. When you add Excel you increase the amount of CO2 regardless of what CO2 is already available. In an unenriched tank the CO2 concentration level is about 8ppm, so adding Excel to this tank improves the amount in the leaf because inside the leaf Excel turns into CO2. So you have the amount of CO2 capture from the water + the amount of CO2 the Excel turns into. That's the best way to think of it.
Cheers,