A method and a device for supply of a dialyser in a dialysis unit with dialysis fluid is disclosed. At least one dialysis fluid concentrate is mixed with water to produce the dialysis fluid. The dialysis fluid concentrate is prepared in a reservoir unit in a given amount. A control and arithmetic unit calculates the dialysis fluid rate (Qd) such that, after a given treatment time (TB) has passed, a given residual amount of dialysis fluid concentrate or no residual amount remains in the reservoir unit. It is preferable to empty the reservoir unit by the end of treatment.