The present invention relates to a blood treatment apparatus having an extracorporeal circuit, having a dialyzate circuit and having a dialyzer which has a blood-side chamber and a dialyzate-side chamber which is separated from the blood-side chamber by a membrane, characterized in that the blood-side chamber is in fluid communication with the extracorporeal circuit and the dialyzate-side chamber is in fluid communication with the dialyzate circuit, and having a preparation unit for the online preparation of a solution, characterized in that the blood treatment apparatus has first means for carrying out a priming mode and has second means for carrying out an initial treatment mode, wherein the first means are configured such that they control the preparation unit such that a flushing solution having a pH of ≥7.3, and preferably of ≥7.4, is prepared and such that the extracorporeal circuit is filled with this flushing solution, and the second means are configured such that they control the preparation unit such that dialyzate having a pH of ≥7.3, and preferably of ≥7.4, is prepared, and such that the dialyzate circuit is filled with this dialyzate, wherein the blood treatment apparatus has a control or regulation unit which operates the first means before the second means.
