Blood treatment device for use in blood treatment therapies, comprising: an extracorporeal blood circuit, a dialyzer and a dialysis fluid circuit, wherein the extracorporeal blood circuit and the dialysis fluid circuit are separated from each other via a membrane provided in the dialyzer, via which blood can be filtered; at least one bag (34, 40, 48), which contains a fluid; at least one weighing device (62, 64, 66) configured to measure and monitor the weight of the at least one bag (34, 40, 48); and at least one fluid pump (36, 46, 56) configured to pump the fluid out of the bag (34, 40, 48) or into the bag (34, 40, 48); and characterized by a control unit, which is configured: to effect an interruption of a fluid supply by stopping the fluid pump (36, 46, 56) when an unexpected weight variation of the bag (34, 40, 48) caused by a malfunction and measured by the weighing device (62, 64, 66) occurs; to temporarily maintain the interruption of the fluid supply, at least until the malfunction disappears; to automatically restart or re-initiate the fluid supply by the fluid pump (36, 46, 56) if the bag (34, 40, 48) or the weight of the bag (34, 40, 48) stabilizes within a predetermined time and the weight variation does not exceed a first predetermined limit value; and to generate an alarm only if the bag (34, 40, 48) or the weight of the bag (34, 40, 48) does not stabilize within the predetermined time and/or if the weight variation exceeds the predetermined first limit value. an extracorporeal blood circuit, a dialyzer and a dialysis fluid circuit, wherein the extracorporeal blood circuit and the dialysis fluid circuit are separated from each other via a membrane provided in the dialyzer, via which blood can be filtered; at least one bag (34, 40, 48), which contains a fluid; at least one weighing device (62, 64, 66) configured to measure and monitor the weight of the at least one bag (34, 40, 48); and at least one fluid pump (36, 46, 56) configured to pump the fluid out of the bag (34, 40, 48) or into the bag (34, 40, 48); and characterized by a control unit, which is configured: to effect an interruption of a fluid supply by stopping the fluid pump (36, 46, 56) when an unexpected weight variation of the bag (34, 40, 48) caused by a malfunction and measured by the weighing device (62, 64, 66) occurs; to temporarily maintain the interruption of the fluid supply, at least until the malfunction disappears; to automatically restart or re-initiate the fluid supply by the fluid pump (36, 46, 56) if the bag (34, 40, 48) or the weight of the bag (34, 40, 48) stabilizes within a predetermined time and the weight variation does not exceed a first predetermined limit value; and to generate an alarm only if the bag (34, 40, 48) or the weight of the bag (34, 40, 48) does not stabilize within the predetermined time and/or if the weight variation exceeds the predetermined first limit value. to effect an interruption of a fluid supply by stopping the fluid pump (36, 46, 56) when an unexpected weight variation of the bag (34, 40, 48) caused by a malfunction and measured by the weighing device (62, 64, 66) occurs; to temporarily maintain the interruption of the fluid supply, at least until the malfunction disappears; to automatically restart or re-initiate the fluid supply by the fluid pump (36, 46, 56) if the bag (34, 40, 48) or the weight of the bag (34, 40, 48) stabilizes within a predetermined time and the weight variation does not exceed a first predetermined limit value; and to generate an alarm only if the bag (34, 40, 48) or the weight of the bag (34, 40, 48) does not stabilize within the predetermined time and/or if the weight variation exceeds the predetermined first limit value.