JBL ProFlora CO2 Cylinder 500 M filled with 500 g CO2 gass. With external valve (W21.8 x 1/14) and cage. Suitable for the JBL CO2 system (m-system) or any other CO2 system with refillable cylinders.JBL ProFlora CO2 Cylinder 500 M+ 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 or a wall mount+ because CO2 liquefies under pressure CO2 pressurised gas cylinders must be in an upright position when in operation+ package contents: refillable cylinder, ready-filled with 500 g CO2, dimensions: 43 x 11 cm, thread W 21.8 x 1/14