Aquarium Filters perform three critical functions in helping you to maintain a healthy and viable aquatic environment — mechanical, chemical and biological filtration. Mechanical filtration, using a filter pad, floss or foam sleeve, screens out large particles of debris and other solid waste. Chemical filtration utilizes media, like activated carbon, to remove pollutants that can cause discolouration and unpleasant odors. And lastly, Biological filtration employs helpful bacteria to eliminate toxic ammonia and nitrite. When choosing an Aquarium Filter be sure to select one that performs each of these vital functions.