Complete CO2 Kits take the guesswork out of adding CO2 to your indoor garden. Grow room CO2 can be used to boost the growing potential of indoor gardens. While ambient CO2 levels are generally in the 350-400ppm range, many indoor plants will benefit from increased CO2 concentration. …Grow room CO2 is created from a variety of sources. Commercial growers and hardcore hobbyists prefer to supplement directly with CO2 from 20lb or 50lb containers. HTG Supply carries everything you need to help your plants grow with CO2, shop now across our selection of Complete CO2 Kits.