Fluval   Chi Filter Pad has two sides that combine to provide thorough and effective mechanical and chemical filtration. Custom-sized, it fits perfectly inside the filter chamber to prevent debris bypass. The polyester side filters out debris and contaminants. The carbon side filters out harmful liquid substances, colorants and odors for a healthy and clean environment. This replacement filter is exclusively designed for Fluval   Chi aquarium filters, 19 Litre (5 U.S. gal.) and 25 Litre (6.6 U.S. gal.) sizes. Includes 3 Filter Pads.