Efficient filtration is a key component for a clean, healthy, thriving aquarium. Typical stocking densities (in relation to water volume) of fish, plants, corals and invertebrates far exceed levels one would ever find in nature. The biological waste products emitted by aquarium inhabitants must be effectively removed and metabolized before they become toxic. Aquarium filters are available in various configurations and should provide mechanical, biological and chemical filtration, as well as oxygenation.