CO2 is an odorless, invisible, and non-flammable gas. It is also
safe for humans in the maximum concentrations recommended for plant
growth. The average level of CO2 in the atmosphere is about 390 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 agreed to be about 1500 PPM. With CO2 enrichment, under
good conditions, plant growth rates and flowering will increase 20-100%.
CO2 can be used from seedling right through harvest.