The Penn Plax Cascade 80 GPH Filter Cartridges with Activated Carbon will improve the quality of your aquarium water and keep your fish healthy. This 3 Pack of Filter Cartridge Replacements is designed to fit the Cascade 80 GPH hang-on power filter and will last 6 to 12 weeks under normal conditions. Activated carbon is great for freshwater aquarium filtration. It has the ability to not only visually clear the water; but trap pollutants in the pores of the carbon so they do not enter the water. This filter cartridge will remove ammonia; nitrites; odors and other harmful toxins from your aquarium to keep it healthy. It has a poly-fiber floss barrier which screens out particulate matter and debris for an extra layer of protection. Within 24 hours you will see a drastic difference in the water quality. Each filter cartridge is perfectly measured to fit into the Cascade 80 Hang on Filter tray without any gaps preventing debris and contaminants from entering back into the water. This filter cartridge is suitable for both freshwater and marine environments. When used together; the Cascade 80 GPH Filter Model CPF1 and Cascade 80 filter cartridges provide maximum protection against water pollutants from harming your fish. This is for one package with three replacement cartridges. Special Packs of Three Replacement Cartridges are available for the following Cascade Hang-On Power Filters: •Cascade 20 uses Replacement Model number CPF6C3 (3 cartridges) •Cascade 80 uses Replacement Model number CPF1C3 (3 cartridges) •Cascade 100 uses Replacement Model number CPF2C3 (3 cartridges) •Cascade 150 uses Replacement Model number CPF34C3 (3 cartridges) •Cascade 200 uses Replacement Model number CPF34C3 (3 cartridges) •Cascade 300 uses Replacement Model number CPF5C3 (3 cartridges)