I do not have a co2 meter but I can say my plants sure liked it one yielded 248 grams dry.. I have seen reviews that show it does raise the co2 significantly .. I will always have one in my tent.. I place the outtake from on the bag directly behind my fan where the intake is so I know it gets spread around my tent..I read that they need light to work properly. I'm reading reviews from people with co2 meters and theyre saying it doesnt increase co2 at all. I'm really intrested in co2 and what it can do for a grow. How do you know its doing anything without a co2 meter?