Abstract: The present invention relates to an apparatus for an extracorporeal blood treatment having an extracorporeal blood circuit in which a dialyzer is arranged and having a dialyzate circuit, wherein the blood circuit is in fluid communication with a first chamber and the dialyzate circuit is in fluid communication with a second chamber of the dialyzer, and wherein the two chambers are separated from one another by a semipermeable membrane, with a dialyzate pump for a conveying of the dialysis solution being present in the dialyzate circuit, wherein the apparatus has a control unit that is configured to operate the apparatus in a first phase and in a second phase following the first phase, wherein the dialyzate pump is operated with a smaller flow rate in the first phase than in the second phase and/or wherein the dialyzate pump conveys a dialysis solution in the first phase that is of a higher concentration with respect to at least one component than in the second phase.