A system for kidney replacement therapy and sodium management, comprising: a dialysate flow loop for circulating a dialysate through a dialyzer from a dialyzer input to a dialyzer output where at least one waste species enters the dialysate; a dialysate regeneration unit for removing at least a portion of the at least one waste species and releasing at least one conductive species to the dialysate or absorbing at least one conductive species from the dialysate; a conductivity detector that measures the conductivity or sodium ion concentration of the dialysate; a sodium management system for generating a sodium-modified fluid for controlled addition to the dialysate in the dialysate flow loop, the sodium-modified fluid generated by the sodium management system from input ultrafiltrate resulting in a sodium ion concentration or conductivity that is higher or lower than the fluid in the dialysate flow loop; wherein the sodium management system is positioned on a bypass conduit; the bypass conduit fluidly connected to the dialysate flow loop bypassing at least a portion of the dialysate flow loop, the bypass conduit having an inlet, located downstream of the dialyzer output and upstream of the dialysate regeneration unit for removing ultrafiltrate from the dialysate flow loop, and an outlet, located downstream of the inlet and either upstream or downstream of the dialysate regeneration unit for adding sodium-modified fluid to the dialysate flow loop, wherein the sodium management system stores sodium ions, and selectively releases the stored sodium ions into the sodium-modified fluid through modulation of an electrical field to increase the sodium concentration of the dialysate; wherein the bypass conduit includes an ultrafiltration pump downstream of the inlet and an ultrafiltrate reservoir downstream of the ultrafiltrate pump, a second conduit fluidly connecting the reservoir to the sodium management system by means of a sodium management pump located between the ultrafiltrate reservoir and the sodium management system, and a third conduit fluidly connecting the sodium management system to the dialysate flow path via the outlet; and wherein the sodium management system is controlled based on an output of the conductivity detector. a dialysate flow loop for circulating a dialysate through a dialyzer from a dialyzer input to a dialyzer output where at least one waste species enters the dialysate; a dialysate regeneration unit for removing at least a portion of the at least one waste species and releasing at least one conductive species to the dialysate or absorbing at least one conductive species from the dialysate; a conductivity detector that measures the conductivity or sodium ion concentration of the dialysate; a sodium management system for generating a sodium-modified fluid for controlled addition to the dialysate in the dialysate flow loop, the sodium-modified fluid generated by the sodium management system from input ultrafiltrate resulting in a sodium ion concentration or conductivity that is higher or lower than the fluid in the dialysate flow loop; wherein the sodium management system is positioned on a bypass conduit; the bypass conduit fluidly connected to the dialysate flow loop bypassing at least a portion of the dialysate flow loop, the bypass conduit having an inlet, located downstream of the dialyzer output and upstream of the dialysate regeneration unit for removing ultrafiltrate from the dialysate flow loop, and an outlet, located downstream of the inlet and either upstream or downstream of the dialysate regeneration unit for adding sodium-modified fluid to the dialysate flow loop, wherein the sodium management system stores sodium ions, and selectively releases the stored sodium ions into the sodium-modified fluid through modulation of an electrical field to increase the sodium concentration of the dialysate; wherein the bypass conduit includes an ultrafiltration pump downstream of the inlet and an ultrafiltrate reservoir downstream of the ultrafiltrate pump, a second conduit fluidly connecting the reservoir to the sodium management system by means of a sodium management pump located between the ultrafiltrate reservoir and the sodium management system, and a third conduit fluidly connecting the sodium management system to the dialysate flow path via the outlet; and wherein the sodium management system is controlled based on an output of the conductivity detector.