This system is designed for the removal of iron and manganese from water. These filters oxidize ferrous iron to turn in into an insoluble Ferric particle (rust), and then trap it in the filter media. Sometimes the oxidizer is injected before the back washing filter tank. The oxidizer could be bleach, ozone or the oxygen in air. This is a 3 step process: oxidizer injection, retention time (for particle growth) and finally filtration. Sometimes the oxidation and filtration can take place in one step. With a two tank design, the tanks clean each other with clean water and the media is kept clean longer. The media may require a regenerant and may be fairly heavy, requiring high backwash rates.