The Lusso Extra Filter is a carbon filter that should be replaced every six months in order to protect your tank from limescale build up. The extra filter is essential to ensure that you remove limescale, magnesium and particles as well as lead, protozoan, cysts and organic compounds. By changing your filter regularly and every six months as advised, you will remove any unwanted tastes such as chlorine and will keep the water fresh from colour. The filter is easy to install and replace.