If a bed of manganese greensand is allowed to become completely exhausted, the Mn++ attached by ion exchange to the zeolite may be lost-exchanged-and require being regenerated by ion exchange before oxidizing it to MnO2 for another cycle of oxidation filtration. Therefore, it is important that manganese greensand installations be regenerated promptly on schedule, rather than waiting until the oxidizing function begins to fail. By then, some of the MnO2 will already be gone from the zeolite, and peak efficiency will be lost.