I run "The Bucket".... It has an organic compound that brakes down and emits CO2 in a bucket through a pump and over the plants every 15 min alternating with my fans ONLY durning light hours... This system will run for 6 to 8 months (depending on useage) before a refill.... I don't waste any CO2 on vegging....PPM is around 1200 unless I have to deal with spidermights then I'll shut the fans down and crank it up to 20,000ppm for 1 hour and that will choke all the mites rite out!