An electrolytic cell (1) comprises an electrode in a chamber including an electrolyte (10) and an electrical power supply (9) arranged to supply electrical energy to the electrode. A current sensor (18) detects electrical current in the cell. A reservoir of a metal salt solution (17) is provided. A controller (19) is arranged to supply metal salt solution from the reservoir to the chamber of the cell in dependence on the current detected at the sensor. This permits the conductivity of the electrolyte to be brought up to required levels quickly, independently of dynamic cell conditions. Previously, metal salt was added gradually to the electrolyte. This was time-consuming and produced inconsistent results.
