A medical fluid system includes a medical fluid pump; a container holding a fluid to be pumped by the medical fluid pump, the fluid at a first time having a first conductivity, the fluid at a second time having a second conductivity; and a radio frequency level sensor positioned in operable relation with the container, the radio frequency level sensor (i) configured to provide an output indicative of a level of the fluid in the container based upon sensing an impedance and (ii) connected to tuning circuitry that minimizes a reactance of the impedance such that the output is at least substantially independent of whether the fluid has the first conductivity or the second conductivity. The medical fluid system can determine the level of the fluid by measuring a resistance, the impedance, or a phase shift seen by the sensor.