Aquarium filters are divided into two types: internal and external, each with its advantages and disadvantages .
Internal filters are divided into: sponge filter, internal filter with electric pump (powerhead) and filter substrate.
Sponge tank filters : This fish tank filter is classic and was used many years ago, now used mostly by fish tanks with shrimp farms. It consisted of an air stone connected to an air pump covered in sponge, but also acts as a mechanical filter and biological filter. Obviously, it is very effective in larger aquariums or densely populated fish tanks.
Internal powerhead aquarium filter: It has a case which contains an electric pump at the top and at the bottom a case that contains filtering materials, mostly sponges. It is suitable for mechanical filtration. If you replace the filter material like sponges with substrate siporax or pro, than it can be used as a biological filtration. This type of filter isn’t recommended to be used in fish tanks with 100 liters capacity or larger. By using a lot amount of space, this characteristic will make it to be somehow unaesthetic.
Substrate fish tank filter: This kind of filter uses pipes or boards, under substrate, whereby water is pushed or pulled by a water pump. The advantage is given by substrate, that becomes a biological filter with a massive volume. Disadvantages can include, inability to use a fertile substrate, the difficulty high enough to mount a filter (especially for the DIY one ) and attention that should be chosen substrate (weight / grit).
External aquarium filters are divided into: HOB filters (hang-on), canister filters and sump tank filters.
HOB filter or waterfall type filter: it looks like a box, that is supported above the one of the aquarium glass walls. It contains a pump that pulls water from the aquarium after it passes through the filter materials and eventually back into the fish tank. The advantage is that no longer occupy place in the aquarium and can be hidden by the wall behind the pool. Be careful though, those who have questionable quality it is possible to make a small noise ( box cover can vibrate because of the engine) .
External canister type filter: It is one of the most practical for our aquariums usual filters. It looks like a can or a box in which the filter material and the cover contains the motor (pump). In this model, the filter canister is located under the aquarium, water drops after that is drawn by the pump through the filter and is pushed back into the aquarium.The advantages are: do not take much space in the tank can be hidden in the cupboard under the aquarium, higher volume for the filter material, easy maintenance and less frequent than in an internal filter. The disadvantage is given by the higher price. Please note: the aquarium filter should be placed below, not near the aquarium and not above the aquarium.
Sump fish tank filter: It is basically another aquarium tank located under the display, and divided into several rooms where the filter material is. The major advantage is that it has a very high volume for filter material, can hide other equipment. It is suitable for large aquariums and marine aquariums densely populated.
Filtration has an essential role in maintaining a healthy environment, free from toxic substances. Filtration is necessary for fish tanks with warm water (freshwater or seawater) and cold water.