Brand new 20 pound aluminum CO2 tank: Perfect for use with our CO2 regulator to boost carbon dioxide levels in your grow room. Aluminum tanks are zbout 1/2 the weight of standard steel tanks, and do not rust or corrode. A 20 lb. tank should last about a month in 5' x 5' grow room, and can be filled at most any beverage distributor or welding supply store for around $25.00. Due to shipping restrictions, tank is shipped empty / not filled.