A dialysate fluid circulation apparatus includes a dialyzer, a first housing and a second housing. The first housing contains material capable of releasing sodium into dialysate fluid flowing through the first housing. The second housing contains material capable of binding sodium ions from dialysate fluid flowing through the second housing. Hydraulic conduit sections are configured to extend between the dialyzer, the first housing, and the second housing to connect the dialyzer with the housings in a primary flow path for dialysate fluid to flow from the dialyzer to the first housing, from the first housing to the second housing, and from the second housing back to the dialyzer.
