Birm is a filter media for the removal of iron and manganese. It Is an aluminium silicate coated with manganese dioxide. Under the proper conditions no chemicals but an air pocket is needed. In that case Birm only needs to be backwashed from time to time with water.

Birm acts as a catalyst to enhance the reaction between dissolved oxygen and the iron compounds, changing the Fe2+ into Fe3+ and form ferric hydroxide that precipitates and may be easily filtered.