Abstract: An ionizer for treating swimming pool water including an enclosure and an electrode housing. The electrode housing is removably secured to a wall of the enclosure and integrally includes a mounting bracket, a hollow cylindrical body, a sensor well, and a projection. The projection sealingly receives a pair of ion-producing electrodes. A vibration sensor is attached to an interior surface of the housing, and is operable to sense when water is flowing through the electrode housing. A method for determining and indicating when the electrodes need replacement is also disclosed.