Secret jardin + co2

will co2 leak out of a secret jardin? if all passive intake air vents are closed and the light is ac. how much co2 would it cost roughly for a 3x3 flowering cycle, also thinking about adding it in veg too (1.4x1.4) also I am trying to think if those co2 bottle for paintball guns would be big enough?

oops shoulda probly posted this in growroom design my bad, but bump to my original question, if a mod can move this to the appropriate area much appreciation!