Eheim Ehfisynth Wool is a fine loose filter wool that can be used as a mechanical filter. It will over time become biologically active can be used in any type of filter. Great to use as a fine polishing media the Eheim Ehfisynth filter wool mechanically polishes aquarium water before it is introduced back into the aquarium. Eheim Ehfisynth removes fine particles of dust from the aquarium which are frequently the cause of cloudy water. Place Eheim Ehfisynth as the final media in a 10mm layer in your external filter. After treatment with any medication Ehfisynth must be replaced.