There is no single filter that fits every aquarium need. Typically, hang-on-back filters work well for beginning aquarists because they provide all three types of filtration – mechanical, biological and chemical – and most models use drop-in cartridges, making them very user friendly. Internal filters go inside the aquarium, allowing users to place the aquarium where space is limited. Canister filters can be loaded with virtually any filter media, making them the most versatile type of filter. They take a little more time and effort to service but do not require cleaning as often as other types of filters. Tanks with messy fish should have good mechanical filtration, while heavily populated aquariums should have extra biological media. To ensure optimal performance, choose a filter rated one size larger than your aquarium.