So you need well water free of contaminants, like the rust that causes orange stains and the sulfur that leads to rotten egg odor.
Iron Defender systems utilize oxygen, contained in your water and fresh ambient air drawn into the filter tank during the cleaning cycle to oxidize Iron, Hydrogen Sulfide and Manganese, so they drop out of solution to form particles. Periodically, the Iron Defender system initiates a backwash cycle so the oxidized particles are flushed from the filter.
Iron Defender systems do not need chemicals for oxidation. However, if your water contains bacteria, water treatment chemicals may be required for disinfection.