Macro Aqua CO2 System Complete Kit w/ Dual Gauge Regulator & 2L Cylinder & Diffuser Includes: Dual Gauge Regulator, 2L Cylinder, Diffuser with Bubble Counter, Air Tube and Cylinder Stand. Aluminum cylinder ships empty. Complete CO2 kit for your planted aquariums. Easy to setup. Fill the cylinder with CO2 and ready to use. Ensures that the most important nutrient is available to plants to maintain vigorous, lush and vibrant growth and condition. High quality diffuser efficiently dissolves CO2 in aquarium water. Holding stand ensures stability upon installation. Large cylinder last much longer than disposable one.