The present invention relates to a combination of a container (30) comprising a connecting portion and of a fluid preparation device (50), in particular a dialysis machine, which fluid preparation device (50) is suitable for mounting and connecting the connecting portion (32) of the container (30), wherein the fluid preparation device (50) comprises at least one line (52) which is in fluid communication with the interior of the container (30) at least in the connected position of the container (30), the container (30) being filled with a first medium and wherein the combination and preferably container (30) comprises a reservoir (100) containing a second medium, wherein the fluid preparation device (50) comprises means for opening (56) the reservoir (100) so that the first and second medium are mixed with each other.
