CO2 is an odorless, invisible, and non-flammable gas. The average level of CO2 in the atmosphere is about 300 PPM (parts per million). If the level decreases down below 200 PPM in an enclosed growing area, plant growth slows to a halt. Through the years of testing and research, the optimum enrichment level of CO2 for plant growth has been established at 1500 PPM. With CO2 enrichment, under good co..