A renal therapy blood cleaning system includes: a blood filtering device in communication with an extracorporeal circuit； a first pump configured to pump fluid to the blood filtering device； a second pump configured to pump fluid from the blood filtering device； a balance chamber in fluid communication with first and second lines, the first and second lines in fluid communication with the first and second pumps, respectively, the balance chamber configured to exchange like volumes of fresh and spent fluid； a plurality of valves； and a control scheme programmed to operate the plurality of valves to enable spent fluid taken from the balancing chamber through one of the first and second lines to be recirculated to the balance chamber through the other of the first and second lines to compensate for a volume of fresh fluid delivered to the blood filtering device.
