A system comprising: a blood fluid removal device comprising (i) an inlet for receiving blood from a patient, (ii) an outlet for returning blood to the patient, (iii) a medium for removing fluid and contaminants from the blood, the medium being positioned between the inlet and the first outlet, and (iv) a fluid source for carrying a fluid, the fluid selected from dialysate and replacement fluid, wherein if the fluid is dialysate the fluid source carries the fluid to the medium, and wherein if the fluid is replacement fluid the fluid source carries the fluid to the blood after the blood exits the medium; a concentrate source (410, 420, 430) for housing a concentrate solution comprising a concentrated component for the fluid; a concentrate flow control element (415, 425, 435) for controlling the rate at which the concentrate solution enters the fluid source; a first sensor for monitoring a cardiovascular parameter of the patient; and control electronics in operable communication with the sensor and the concentrate flow control element, wherein the control electronics are configured, via the concentrate flow control element, to adjust the rate at which the concentrate solution enters the fluid source based on data obtained from the sensor; and wherein the pH and electrolyte concentration of a replacement fluid is set or adjusted based on data obtained from the sensor. a blood fluid removal device comprising (i) an inlet for receiving blood from a patient, (ii) an outlet for returning blood to the patient, (iii) a medium for removing fluid and contaminants from the blood, the medium being positioned between the inlet and the first outlet, and (iv) a fluid source for carrying a fluid, the fluid selected from dialysate and replacement fluid, wherein if the fluid is dialysate the fluid source carries the fluid to the medium, and wherein if the fluid is replacement fluid the fluid source carries the fluid to the blood after the blood exits the medium; (i) an inlet for receiving blood from a patient, (ii) an outlet for returning blood to the patient, (iii) a medium for removing fluid and contaminants from the blood, the medium being positioned between the inlet and the first outlet, and (iv) a fluid source for carrying a fluid, the fluid selected from dialysate and replacement fluid, wherein if the fluid is dialysate the fluid source carries the fluid to the medium, and wherein if the fluid is replacement fluid the fluid source carries the fluid to the blood after the blood exits the medium; a concentrate source (410, 420, 430) for housing a concentrate solution comprising a concentrated component for the fluid; a concentrate flow control element (415, 425, 435) for controlling the rate at which the concentrate solution enters the fluid source; a first sensor for monitoring a cardiovascular parameter of the patient; and control electronics in operable communication with the sensor and the concentrate flow control element, wherein the control electronics are configured, via the concentrate flow control element, to adjust the rate at which the concentrate solution enters the fluid source based on data obtained from the sensor; and wherein the pH and electrolyte concentration of a replacement fluid is set or adjusted based on data obtained from the sensor.