Pre-filter mat and filter fleece for cleaning. The porous material is evenly permeated by water and retains both coarse and fine dirt particles. After a short acclimatization period, cleaning bacteria settle in the structured special foam, which ensures intensive biological pollutant degradation. The fleeces and mats from Eheim are reusable multiple times. For cleaning, they should only be rinsed and squeezed to avoid completely destroying the bacterial cultures.