Penn Plax Cascade Hang-on Aquarium Filter with Quad Filtration System Hang on aquarium filter quietly delivers 150 gallons per hour of crystal clear water for your fresh or marine aquariums from 20 to 35 gallons in size. Revolutionary Bio-Falls Quad-Filtration system provides efficient filtration with anaerobic bacteria for additional ammonia and nitrite removal providing maximum oxygenation. Activated carbon cartridge removes harmful chemicals, toxins, odors, discoloration, and other contaminants for your aquarium. Internal sponge optimizes colonization of beneficial anaerobic bacteria and polyfiber floss cartridge traps floating particulate matter. Adjustable flow knob allows you to reduce filtration during feeding times or as needed. Aquarium filter is recommended for both freshwater and saltwater applications.