I had my tank filled at the growshop, but when i get my paintball tanks refilled, the large cylinders say 100% CO2 on the tanks, if they put in anything else(besides minute impossible to remove amounts of CO, N, O2, etc), that would be fraud. At the grow shop, the= co2 comess from a beverage company, so the tanks are prolly sanitized and have a purer content. Even medical grade CO2 can contain CO, N, He, O2, etc