A blood treatment apparatus comprising: - a dialysis filter or a receptacle for a dialysis filter; - a dialysis fluid supply line having a first connector for supplying dialysis fluid to the dialysis filter; - a dialysate discharge line having a second connector for discharging dialysate from the dialysis filter; - a blood leak sensor configured and arranged to detect blood in or on the dialysis filter, in the dialysis fluid supply line and/or in the dialysate discharge line, and configured to emit a blood leak signal if blood is detected; - a short-circuit line for connecting the dialysis fluid supply line and, or with, the dialysate discharge line in fluid communication, the short-circuit line comprising hereto a third connector and a fourth connector intended to be respectively connected with one of the first and second connectors (3, 7); - a controller configured to receive the blood leak signal and characterized in that the controller is further configured to emit a signal which, in cooperation with the blood treatment apparatus, performs one, or at least one step from the group consisting of: - issuing a warning to the user that a cleaning of the third and/or fourth connector/s (15, 17) is necessary; - initiating a required or predetermined cleaning of the third and/or fourth connector/s (15, 17); - preventing the usability of the blood treatment apparatus, until the user has performed at least one required activity, and - mechanically preventing the connection of the third and/or fourth connector/s (15, 17) with the first and/or second connector/s (3, 7); when a blood leak signal has been emitted and/or received. - a dialysis filter or a receptacle for a dialysis filter; - a dialysis fluid supply line having a first connector for supplying dialysis fluid to the dialysis filter; - a dialysate discharge line having a second connector for discharging dialysate from the dialysis filter; - a blood leak sensor configured and arranged to detect blood in or on the dialysis filter, in the dialysis fluid supply line and/or in the dialysate discharge line, and configured to emit a blood leak signal if blood is detected; - a short-circuit line for connecting the dialysis fluid supply line and, or with, the dialysate discharge line in fluid communication, the short-circuit line comprising hereto a third connector and a fourth connector intended to be respectively connected with one of the first and second connectors (3, 7); - a controller configured to receive the blood leak signal and characterized in that the controller is further configured to emit a signal which, in cooperation with the blood treatment apparatus, performs one, or at least one step from the group consisting of: - issuing a warning to the user that a cleaning of the third and/or fourth connector/s (15, 17) is necessary; - initiating a required or predetermined cleaning of the third and/or fourth connector/s (15, 17); - preventing the usability of the blood treatment apparatus, until the user has performed at least one required activity, and - mechanically preventing the connection of the third and/or fourth connector/s (15, 17) with the first and/or second connector/s (3, 7); when a blood leak signal has been emitted and/or received. - issuing a warning to the user that a cleaning of the third and/or fourth connector/s (15, 17) is necessary; - initiating a required or predetermined cleaning of the third and/or fourth connector/s (15, 17); - preventing the usability of the blood treatment apparatus, until the user has performed at least one required activity, and - mechanically preventing the connection of the third and/or fourth connector/s (15, 17) with the first and/or second connector/s (3, 7);