Fluval Chi Filter Pads are exclusively designed for Fluval Chi aquarium filters (5 and 6.6 gallon sizes). These pads have two sides that combine to provide thorough and effective mechanical and chemical filtration. It is custom-sized, so it fits perfectly inside the filter chamber to prevent debris bypass. The polyester side filters out debris and contaminants while the carbon side filters out harmful liquid substances, colorants, and odors for a healthy and clean aquarium environment.