Hagen 12-Pack Fluval U4 Poly/Carbon Cartridge Aquarium Water Filter
Fluval Poly/Carbon Cartridges features two sides for effective chemical filtration, the crucial second stage in the filtration process. The polyester filter pad side filters out fine debris and contaminants. The Carbon side filters out harmful liquid substances, colorants and odors. For freshwater, marine or reptile environments. For U series filter model: U4.