Types of Aquarium Filters
Choosing the correct aquarium filtration system is as important as choosing the right tank size and the correct balance of fish. A good filter will help you create a functional environment where your animals will thrive. A poor filter can cause illness among fish, require more tank maintenance, and weaken your aquarium ecosystem. There are several types of commonly available tank filters, and each has strengths and weaknesses.
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Corner Box Filters
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This type of aquarium filter fits in one corner of the tank, directly on the tank gravel. Corner box filters use an air pump, which pump air into the bottom of the box, through the filter and out the top. This air draws water with it, allowing the tank to cycle. Corner boxes perform all three major types of filtration: mechanical, chemical and biological, but their low flow rate restricts efficiency. They need regular cleaning to work properly.
Sponge Filters
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Sponge aquarium filters use a U-shaped tube to pull water through a sponge. The sponge has a large surface area, which aids mechanical filtration and harbors bacteria for biological filtration. Sponge filters are inexpensive and simple to maintain by simply washing the sponge in aquarium water once per week. This type of filter is limited in its efficiency and is best for small tanks and breeding tanks, where it will not catch or injure fry (baby fish.)
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Under-gravel Filters
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Under-gravel filters use a slotted plate and uplift tubes to filter water. An air stone or power head draws water through the gravel substrate and into the tubes. The substrate provides mechanical filtration as well as a home for beneficial bacteria. Some models include activated carbon for chemical filtration. An under-gravel filter requires minimal maintenance: Simply clean the gravel regularly. These filters do not provide highly efficient filtration, which limits the number of fish per tank.
Power Filters
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Also referred to as HOB or hang-on-back filters, power filters offer all three types of filtration and easy maintenance. They're self-contained units that include the pump and a filter cartridge. Water in a power filter passes first through a foam material, which also harbors bacteria for biological filtration, then through an activated carbon cartridge. Power filters can clog easily and must be rinsed on a regular basis. They are not suitable for planted aquariums, but are moderately inexpensive.
Canister Filters
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A canister filter is a type of external aquarium filter that is usually placed below the aquarium. They can be purchased as a self-contained unit or as modular filters. They provide high-quality filtration and are capable of performing all three filtration types. Biological filtration is somewhat limited due to oxygen levels inside the filter. These filters are moderately expensive and require regular maintenance.
Wet/Dry Filters
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Wet/dry filters are placed beneath the aquarium,and are made up of two boxes: One is located in the water and the other is outside the aquarium. They're connected by a U-tube that siphons water between the boxes. Wet/dry filters use a sponge for mechanical filtration and special media for chemical and biological filtration. They provide the highest-quality filtration, but also are much more costly.
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