Skip to the beginning of the images gallery JBL Proflora m500 (Co2 Cylinder)Refillable storage cylinder with 500g CO2. Key Features: CO2 storage cylinder for all CO2 systems. Supplies aquarium plants with their main nutrient carbon dioxide (CO2) while preventing algae TV tested, refillable 500g CO2 reusable cylinder (thread W 21. 8 x 1 14). With pressure relief valve for safety Does not stand on its own. Requires a stand (JBL PROFLORA CO2 CYLINDER STAND) or a wall mount (JBL PROFLORA CO2 CYLINDER WALLMOUNT) Because CO2