6 plants = ? Co2

I have 6 plants in a 5 x 5 (25 sq ft.) space.

Do I need CO2?

Currently I have a fan blowing the air around with the door ajar.

If I need Co2... How much do i need?

I plan on making 2 liter bottles with sugar/water/yeast. Any suggestions to how many i may need?

Thanks.

hellllllllllllllllllllllllllllooooooooooooooooooooooooooooooooooooooo?