Cascade Internal FilterThe Penn Plax Cascade Internal Filter by Penn Plax is designed for better filtration and aeration above and below the surface! The spray bar distributes water evenly over the waters surface to aid in aeration for healthier, cleaner aquarium water. Efficient chemical and biological aquarium filtration Removes harmful toxins, odors, discoloration and more Spray bar provides essential aeration for healthier environment The Cascade Internal Filter