Aqueon Replacement Filter Cartridges are dual-sided, featuring dense-floss with over 25% more activated carbon than the leading brands. These patented cartridges were designed to ensure even distribution of activated carbon. To use, simply rinse under cold water and easily install using the "FRONT" orientation tab. Aqueon Replacement Cartridges are available in: X-Small, Small, Medium and Large. Aqueon products offers a wide range of items so that you can build and maintain a healthy aquatic environment. All the essentials from fish tanks, filters, lighting, food, care, and other supplies that your pet fish needs. We make it easy for you to get your first aquarium and to grow in the hobby as you become more of a fish expert with every step you take and every new thing you learn. For those seasoned hobbyists, we are committed to aquarium product innovation so that we continue to offer products that get you excited. With the Aqueon brand, it's all about the fish.