Polystyrene sulfonate resin for use with a hemodialysis system having a controlled compliance dialysis circuit

A system for performing kidney replacement, comprising:

• an extracorporeal circuit and a dialysis circuit, the dialysis circuit having a sorbent cartridge for removing at least one waste species from a dialysate, one or more conduits for carrying dialysate between the sorbent cartridge and a dialyzer, and a dialysate pump for conveying dialysate from the sorbent cartridge, to the dialyzer and back to the sorbent cartridge;
• and
• a polystyrene sulfonate resin cartridge and one or more conduits for carrying dialysate from the dialysis circuit through the polystyrene sulfonate resin cartridge, and
• one or more controllers for controlling a flow of the dialysate through the sorbent cartridge and through the polystyrene sulfonate resin cartridge,
• wherein the polystyrene sulfonate resin cartridge contains a polystyrene sulfonate resin substantially saturated with calcium ions and the polystyrene sulfonate resin cartridge removes one or more selected from the group consisting of sodium ions, carbonate ions, sulfate ions and phosphates from the dialysate.