Filtration is the method by which you maintain the clarity and purity of aquarium water, thereby increasing your chances of success in keeping aquatic animals. Filtration in natural situations is accomplished through the actions of a variety of plants and animals and microorganisms that utilize the waste products and dead bodies of other creatures. While some of these natural processes can be duplicated to a limited extent in the aquarium, you must, except in very unique circumstances, incorporate artificial processes and mechanical equipment as well.