Oh man.... People who think they need additional Co2 in a little grow tent like that.
Co2 is for sealed grow spaces. You are just exhausting all the Co2 into your house. There is plenty of Co2 in a house for a little grow.
I did not seal it yet, I am just getting stuff together but it will be sealed and as well it is in a walk in closet that is mostly sealed right now, I just need to do the door once I get the dehumidifier for the closet in so I don't run into water problems but it WILL be sealed.
I am using co2 BECAUSE I have a small grow room. To minimize growth/flower time and maximize yields it helps. Since it is a small space and a small grow room, it doesn't use much co2 at all. I am not saying that my thought pattern is correct or makes sense, maybe it doesn't, would need others opinions.
I have some plastic sheeting that you use as a vapor barrier in houses to seal up the tent. Any big leaks will be taken care of like the bottom vents, and the side windows. I don't care about little leaks from the zipper of the main door or the thread holes. I may silicone the thread holes if I can, and the closet it is in will not leak either, I have sealed everything in there except the door, not sure how good I can seal it but I think I can do a pretty good job. I got thick weather insulation to stick and compress when the door closes, should be quite tight or leak very slowly.
I had this co2 on my fish tank when it was establishing the plants for a year, I stopped using it once it was established because it grew like nuts and it was way too much maintenance trimming plants. Rather than let it just sit there collecting dust, I am using it. I don't mind trying it or the few bucks it costs to fill it.