Conductivity control systems

A dialysis system has a module with a dialyzer configured to remove one or more substances from a dialysis solution as it passes through a dialyzer. The module has a fluid line, a sorbent cartridge, and a sodium control system adapted to actively alter a sodium concentration of dialysis solution passing through the fluid line as the dialysis solution exits the sorbent cartridge. The sodium control system has a conductivity sensor that sends a signal indicating the conductivity of the dialysis solution as the dialysis solution exits the sorbent cartridge, the conductivity meter being in communication with the sodium control system, a processor configured to receive the signal from the conductivity sensor, compare the conductivity signal to a threshold value lower than a prescription value, and cause the sodium control system to stop actively altering the sodium concentration if the signal is greater than the threshold value.