Juwel Cirax is a highly porous filter material that utilises its extremely large surface area to provide effective biological filtration. To maintain this water quality, Juwel suggest replacing Cirax every 9 - 12 months. Do not however remove all the Cirax from your filter at the same time, as this will remove the most important element of your filtration system, your beneficial bacteria. Instead, replace the media in stages, ensuring the new media has sufficient time to become colonised.