Interpet Polymer Filter Wool provides effective removal of fine particles to maintain excellent water clarity. This product is fantastic at polishing the water. Can be cleaned and reused, and does not affect water chemistry. Particles of food, decayed organic material and inorganic \'mulm\' cause water quality problems, harbour disease and spoil the appearance of the aquarium. Large particles should be removed by coarse filter media to prevent them blocking the filter. Fine particles which pass through the coarse media will still spoil the water clarity, so water should then be passed through polymer filter wool. How to use: 1. Insert the polymer wool as the final stage of filtration, e.g. at the top of an external cannister filter or box filter 2. Ensure even coverage across the filter vessel to prevent particles bypassing the media. 3. The firmer media is packed, the finer the particles trapped. 4. When the media becomes blocked, remove and clean under a tap. Replace filter wool when it becomes excessively worn or dirty.