Keep your tank clean and clear with the genuine Penn Plax filter cartridge to fit your Cascade 150 or 200 hang-on power filter models CPF3 and CPF4. Activated carbon is great for freshwater aquarium filtration. It has the ability to remove odors; and water discoloration by trapping the pollutants in the pores of the carbon. The poly-fiber floss barrier screens out particulate matter and debris keeping the water clean; clear; and healthy. No assembly required keeping your hands clean. Easily install into interior compartment of your hang on filter. Suitable for freshwater and saltwater tanks. Perfectly measured to fit into the Cascade 150 or 200 filter tray without any gaps preventing debris and contaminants from passing through back into the water.