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 operation of the level sensor configured so as to be (i) indicative of a level of the fluid in the container and (ii) 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 medical fluid by measuring the resistance, impedance or phase shift seen by the sensor.