An extracorporeal blood treatment apparatus is provided comprising a filtration unit (2) connected to a blood circuit (17) and to a dialysis fluid circuit (32), a preparation device (9) for preparing and regulating the composition of the dialysis fluid a control unit (12) is configured for determining or receiving a proposed value (Condprop) of a conductivity for the dialysis fluid in the dialysis supply line (8) and to determine a set value (Condset) for the conductivity in the dialysis fluid as a function of the proposed value (Condprop) and as a function of at least one of a second parameter (UF volume/W WL/W) indicative of a patient fluid overload and a third parameter (gconc) chosen in the group including: a glucose concentration in the patient and a concentration-related parameter of at least glucose in the patient.
