A dialysis system comprising: a blood circuit comprising: a fixed flow peristaltic blood pump; tubing for conveying blood between the peristaltic blood pump and a patient, wherein the tubing comprises an arterial line configured to convey blood from a patient to the fixed flow peristaltic blood pump and deliver the blood to a dialyzer and a venous line configured to convey treated blood from the dialyzer to the patient; an arterial pressure sensor (72a, 72b, 360a, 360b) for measuring a pressure of blood flowing through the arterial line; a venous pressure sensor for measuring a pressure of blood flowing through the venous line; and a controller in communication with the arterial and venous pressure sensors and configured to: calculate hydraulic impedances within the arterial line and venous line of the tubing based on: signals received from the arterial and venous pressure sensors, the signals indicative of the pressures of the blood flowing through the arterial and venous lines; and blood flow rate data for blood flow through the blood circuit, the blood flow rate data inferred directly from pump speed of the peristaltic blood pump; compare one of the calculated current hydraulic impedance values to a baseline hydraulic impedance value; and detect a blood flow degradation in the dialysis system based on the comparison. a fixed flow peristaltic blood pump; tubing for conveying blood between the peristaltic blood pump and a patient, wherein the tubing comprises an arterial line configured to convey blood from a patient to the fixed flow peristaltic blood pump and deliver the blood to a dialyzer and a venous line configured to convey treated blood from the dialyzer to the patient; an arterial line configured to convey blood from a patient to the fixed flow peristaltic blood pump and deliver the blood to a dialyzer and a venous line configured to convey treated blood from the dialyzer to the patient; an arterial pressure sensor (72a, 72b, 360a, 360b) for measuring a pressure of blood flowing through the arterial line; a venous pressure sensor for measuring a pressure of blood flowing through the venous line; and a controller in communication with the arterial and venous pressure sensors and configured to: calculate hydraulic impedances within the arterial line and venous line of the tubing based on: signals received from the arterial and venous pressure sensors, the signals indicative of the pressures of the blood flowing through the arterial and venous lines; and blood flow rate data for blood flow through the blood circuit, the blood flow rate data inferred directly from pump speed of the peristaltic blood pump; compare one of the calculated current hydraulic impedance values to a baseline hydraulic impedance value; and detect a blood flow degradation in the dialysis system based on the comparison. calculate hydraulic impedances within the arterial line and venous line of the tubing based on: signals received from the arterial and venous pressure sensors, the signals indicative of the pressures of the blood flowing through the arterial and venous lines; and blood flow rate data for blood flow through the blood circuit, the blood flow rate data inferred directly from pump speed of the peristaltic blood pump; signals received from the arterial and venous pressure sensors, the signals indicative of the pressures of the blood flowing through the arterial and venous lines; and blood flow rate data for blood flow through the blood circuit, the blood flow rate data inferred directly from pump speed of the peristaltic blood pump; compare one of the calculated current hydraulic impedance values to a baseline hydraulic impedance value; and detect a blood flow degradation in the dialysis system based on the comparison.