I'm running 2 exhale standard size Co2 bags in a 2 x 4 ft tent. I'm using an Auto Pilot ($100) temp,humidity, Co2 meter inside I run from 550 ppm lights out up to about 1000+ ppm lights on with an exhaust fan running. https://www.amazon.com/Hydrofarm-Autopilot-Desktop-Monitor-Logger/dp/B01FYWU2IS/ref=pd_lpo_sbs_86_t_0/145-3135595-8031458?_encoding=UTF8&psc=1&refRID=MWK6W