CO2 storage bottle for all CO2 systems. Supplies aquarium plants with their main nutrient carbon dioxide (CO2) and thus prevents algae,TÜV-tested, refillable CO2 reusable bottle. With pressure relief valve for safety,has a stand and stands on its own. Does not require a holder,as CO2 liquefies under pressure, CO2 pressurised gas cylinders must stand vertically in operation.