The Fluval 3 Plus Carbon Filter Pad with high-quality impregnated active carbon has been specially developed as a fine filter medium for the Fluval 3 Plus Underwater Filter. It is particularly suited to filtering out harmful liquid substances, dyes, medicines and extremely fine suspended particles and contaminants. It improves the clarity, color and smell of the water. The Fluval 3 Plus Carbon Filter Pad does not alter properties of aquarium water.