A dialysis system (10, 210, 310) comprising: a sorbent cartridge (32, 116, 200a, 200b, 300a, 300b) in fluid communication with at least one of a patient or a dialyzer (20, 108, 212, 312), the sorbent cartridge including a housing having (a) a zirconium phosphate layer (60, 63, 72, 76, 88) followed by at least one of a urease layer (62, 74, 84), a zirconium oxide layer (64, 78, 86, 90), or a carbon layer (66, 80, 92), or (b) a urease layer (62, 74, 84) followed by a zirconium phosphate layer (63, 76, 88); a storage container (26, 104, 114, 224a, 224b, 230, 324, 330) in fluid communication with the sorbent cartridge; a pump (110, 218, 220, 232, 320, 332) in fluid communication with the sorbent cartridge and the storage container; and characterised by a control unit (250, 350) in operable communication with the pump, wherein the control unit is programmed to cause the pump to pump a dialysis fluid to flow (i) in a first direction through the sorbent cartridge, wherein the zirconium phosphate layer is contacted by the dialysis fluid before the at least one of the urease layer, zirconium oxide layer or carbon layer in the housing having a zirconium phosphate layer followed by at least one of a urease layer, a zirconium oxide layer, or a carbon layer, or the urease layer is contacted by the dialysis fluid before the zirconium phosphate layer in the housing having a urease layer followed by a zirconium phosphate layer, and (ii) in a second direction, reverse from the first direction, through the sorbent cartridge wherein the at least one of the urease layer, zirconium oxide layer or carbon layer is contacted by the dialysis fluid before the zirconium phosphate layer in the housing having a zirconium phosphate layer followed by at least one of a urease layer, a zirconium oxide layer, or a carbon layer, or the zirconium phosphate layer is contacted by the dialysis fluid before the urease layer in the housing having a urease layer followed by a zirconium phosphate layer. a sorbent cartridge (32, 116, 200a, 200b, 300a, 300b) in fluid communication with at least one of a patient or a dialyzer (20, 108, 212, 312), the sorbent cartridge including a housing having (a) a zirconium phosphate layer (60, 63, 72, 76, 88) followed by at least one of a urease layer (62, 74, 84), a zirconium oxide layer (64, 78, 86, 90), or a carbon layer (66, 80, 92), or (b) a urease layer (62, 74, 84) followed by a zirconium phosphate layer (63, 76, 88); a storage container (26, 104, 114, 224a, 224b, 230, 324, 330) in fluid communication with the sorbent cartridge; a pump (110, 218, 220, 232, 320, 332) in fluid communication with the sorbent cartridge and the storage container; and characterised by a control unit (250, 350) in operable communication with the pump, wherein the control unit is programmed to cause the pump to pump a dialysis fluid to flow (i) in a first direction through the sorbent cartridge, wherein the zirconium phosphate layer is contacted by the dialysis fluid before the at least one of the urease layer, zirconium oxide layer or carbon layer in the housing having a zirconium phosphate layer followed by at least one of a urease layer, a zirconium oxide layer, or a carbon layer, or the urease layer is contacted by the dialysis fluid before the zirconium phosphate layer in the housing having a urease layer followed by a zirconium phosphate layer, and (ii) in a second direction, reverse from the first direction, through the sorbent cartridge wherein the at least one of the urease layer, zirconium oxide layer or carbon layer is contacted by the dialysis fluid before the zirconium phosphate layer in the housing having a zirconium phosphate layer followed by at least one of a urease layer, a zirconium oxide layer, or a carbon layer, or the zirconium phosphate layer is contacted by the dialysis fluid before the urease layer in the housing having a urease layer followed by a zirconium phosphate layer.