At Onlineaquariumspullen we have a professional CO2 filling station on location. With this filling station we can fill CO2 bottles with a volume of up to 10 kilos. A requirement here is of course that the bottle has a valid inspection date. In addition, we can only fill bottles with a screw thread W 21.8 x 1/14. This is the usual size for almost all aquarium CO2 bottles & systems.