run it all the way threw.

I did see a video on you tube by advanced nutrients and they did say that the plant uses the most co2 at the beggining of flowering. I also read the same thing in a urban garden mag. either way both things I read the growers still ran co2 till the end, just lowered it a bit after the first few weeks or so. (you might want to research further, I have only read these things not experienced them)
either way I have never heard co2 would decrease yield