Marineland C-Series Canister Filter Polishing Filter Pads PC 530 2-PackIn order to create and maintain a clean, healthy aquatic environment, three stages of filtration are required: Mechanical, Chemical and Biological. Aquarium water is drawn into the canister and through a succession of stacked media trays for full contact filtration virtually no bypass. The water is then returned to your aquarium, sparkling clean and fish healthy. And when its time to service your C Series canister filter, all you do is push a lever,