The present invention relates to a combination of a container comprising a connecting portion and of a fluid preparation device, in particular a dialysis machine, which fluid preparation device is suitable for mounting and connecting the connecting portion of the container, wherein the fluid preparation device comprises at least one line which is in fluid communication with the interior of the container at least in the connected position of the container, the container being filled with a first medium, wherein the combination and preferably container comprises a reservoir containing a second medium, wherein the fluid preparation device comprises means for opening the reservoir so that the first and second medium are mixed with each other.
