These carbon infused polyester filter pads are specially designed for use with all current and previous Fluval Chi aquarium systems. They help to remove small particles and debris that can cloud water. For best results, rinse filter pads thoroughly before first usage (we recommend rinsing anything you place in your filter or tank). Place the filter pad (white side up) on top of the foam sponge pad. Rinse your filter pad weekly, using water from your tank. Replace filter pad every 2-4 weeks, but never replace the foam and polyester filter pads at the same time.