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. Neutralizes the chlorine and chloramines typically found in tap water, making it safe for fish. Helps to reduce the stress on fish as they become familiar with their new environment. Helps restore the natural slime coat to skin and gills, which can be worn away from netting and transporting fish.