A system for dialysis is disclosed. The system includes a dialyzer having dialysis fluid inlet and outlet ports, a blood pump connected to the dialyzer for pumping blood from a patient, at least one drip chamber in series with the dialyzer, a source of fresh dialysis fluid in series with the dialysis fluid inlet port, a pump connected with the source of the fresh dialysis fluid, and at least one of a balance chamber or a flow channel between the dialysis fluid outlet port and the dialysis fluid inlet port for balancing a flow of fresh dialysis fluid and spent dialysis fluid to the dialysis fluid inlet port. A number of passes of spent dialysis fluid through the dialyzer is set by a ratio of a flow of spent dialysis fluid within the dialyzer to a flow of fresh dialysis fluid to the dialyzer.
