In most cases with iron content in the water, the water itself will usually contain different types of contaminants, sediments, dirt, etc. When your water filter stops passing water, it's incorrect to believe that only iron content is the cause. The inlet woven filter on the Iron Manganese Filter will be clogged with dirt or sediment.
The Iron Manganese Filter is specialized in filtering out iron manganese content but is minimally equipped to deal with tiny amounts of sediment and dirt. Since iron water will often have large amounts of dirt and sediment, a Sediment Pre-Filter is REQUIRED if the Iron Filter following it, or any filter following the Sediment Filter for that matter, is to properly work as intended without clogging up too early.