Filters
Filters are used to provide mechanical, chemical, and biological filtration. Filters clean solid wastes from the water, remove chemical and heavy metal from aquarium water and support colonies of nitrifying bacteria to allow them to change ammonia and nitrite in less harmful nitrate.
Powerheads
	These do not provide any mechanical, chemical, and biological filtration themselves. But they do power some other filters. They are electrically powered pumps which are not suitable for small aquariums because they are too powerful.
Internal Box filters
	These are usually box shaped filters that are powered by air pumps. Internal box filters are old fashioned filters, but still useful for small quarantine or hospital aquariums.
External Box Filters
	These are usually box shaped filters that hang on the outside of the aquarium. Many have internal chambers that are designed to hold different types of filter media. Usually powered by electric water pumps, but can also be powered by air pump. These filters are still popular in the USA. Especially the bio-wheel version of these external box filters. The Bio-wheel has a long star shaped foam drum on the top of the filter, which looks like a water wheel when in operation. It has been reported to be a very effective biological filter and also very good at oxygenating the aquarium water.
Internal Canister Filters
	These filters are usually box shaped with water inlets cut into the sides; they are totally submerged in the aquarium water. They have various types of foam filter media in stacked baskets. The canister is powered by a powerhead.
External Canister Filters
	These filters are boxes with two plastic pipes, One pipe siphons water out of the aquarium, the other pumps it back in to the aquarium. They are powered with electric water pumps. These have stacked baskets inside; the baskets can hold various different filter media.
Sponge Filters
	These are air powered sponge filters. Simple sponge filters are made from a hard plastic U-shaped pipe. One side of the pipe has large holes in it, to allow water to flow into the pipe. This side of the pipe is covered by a foam sponge. The other side has air pumped in which forces the water through the sponge and around the pipe towards the water surface. These filters are popular in breeding tanks.
Undergravel Filters
	These filters are powered by air pumps or powerheads. At the bottom of the aquarium, there is a perforated plastic plate with 2-3 in of gravel placed on top. With a vertical plastic pipe connected to the plate under the gravel. The water can be sucked or pumped through the pipe. This type of filter is considered to be dirty and hard to maintain.
Trickle Filters
	These filters can be placed above or below an aquarium. They have stacked filter media inside, which gets water sprayed on it, from a spray bar situated on the top of the stack filter media, the water then trickles down through the filter media. The advantage of this is that the water exiting the filter has high oxygen content.
Protein Skimmer
	This works well in saltwater aquarium but is considered to be useless in fresh water aquariums. It works by collecting waste that sticks to air bubbles, the bubbles rise to the top of the filter where it can be removed from inside a cup situated on the top of the protein skimmer.