Biogents suggests 20 pound or larger CO2 bottles which are also used in pubs and restaurants. Such a bottle lasts for three to seven weeks depending on the flow rate used. These can be acquired or rented at drink retailers or bottle depots for a deposit. A door-to-door delivery service may also be possible in some locations. How often you need to change the tank depends on: 1. what size you use and 2. which release rate of CO2 you use. Our CO2 traps give you the option of deciding between two flow rates: standard and high. This allows you to adapt the release of CO2 to the mosquito situationThe flow rate can be adjusted to the local situation. We recommend a consumption of about 1.1 lbs/day. CO2 bottles are available at gas stores and gastronomy suppliers.To most efficiently utilize CO2 with your trap, we recommend releasing the gas only at times of peak mosquito activity and shutting it off when mosquitoes are not flying as much. By releasing gas on a fixed schedule, you can greatly extend the time between refills. This can be accomplished either manually turning on and off the gas at the tank, or automatically using the BG CO2 timer. The timer connects between the gas manifold and the trap and uses a 9V battery-operated timer to can switch on and off your CO2 flow. You can program up to 2 distinct release intervals each day to correspond to dusk and dawn activity patterns.You can find it here: https://www.luxebackyard.com/products/bg-co2-timer-clock-timer-biogents