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 , which contains a fluid; at least one weighing device configured to measure and monitor the weight of the at least one bag ; and at least one fluid pump configured to pump the fluid out of the bag or into the bag ; and characterized by a control unit , which is configured: to effect an interruption of a fluid supply by stopping the fluid pump when an unexpected weight variation of the bag caused by a malfunction and measured by the weighing device 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 if the bag or the weight of the bag 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 or the weight of the bag 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 , which contains a fluid; at least one weighing device configured to measure and monitor the weight of the at least one bag ; and at least one fluid pump configured to pump the fluid out of the bag or into the bag ; and characterized by a control unit , which is configured: to effect an interruption of a fluid supply by stopping the fluid pump when an unexpected weight variation of the bag caused by a malfunction and measured by the weighing device 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 if the bag or the weight of the bag 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 or the weight of the bag 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 when an unexpected weight variation of the bag caused by a malfunction and measured by the weighing device 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 if the bag or the weight of the bag 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 or the weight of the bag does not stabilize within the predetermined time and/or if the weight variation exceeds the predetermined first limit value. <EOS>