Which Filter for your Fish Tank (Aquarium)


“Which filter should I get for my aquarium?”

The most common question in fish keeping is: “which filter should I get?” Below are some filters and explanations of the most common used filters on the market today. This should help aid you in which filter to choose.


To start off, lets discuss the three types of filtration that there are and that are needed in a fish tank (aquarium).

1) Mechancial

Mechanical filtration involves the removal of waste particles and debris by passing water continuously through a powered machine. Because waste is constantly being produced in your tank by fish everyday, a mechanical filter is a must.

2) Chemical

Ammonia, metals, and odors are all bad substances that should be removed from a fish tank to provide a healthy and stable aquarium. A chemical filter is what you need to do the job. Most chemical filters use carbon as their main material to pass the water through. Carbon collects most of these substances when water flows through and helps aid in keeping bad dissolved particles out of your tank.

3) Biological

Every fish in your tank will produce waste which needs to be somehow filtered out. Without proper filtration for the waste, a lethal bacteria will grow and harm your fish tank. Now, although mechanical filters filter out most of the waste, there are still some waste particles that cannot be filtered out completely.  Biological filters do the job!  In biological filtration, two types of beneficial bacteria known as “nitrofiers” grow in the tank and convert harmful wastes into something less harmful which results into nitrate (nitrogen).


Now that you have an understanding of the types of filtration… let’s get into some filters

Under-gravel Filters

Under-gravel filters are filters you are going to want to go with when you are dealing with fish tanks that are 10-30 gallons big or fish tanks with a small fish count. Under-gravel filters are placed underneath a layer of aquarium substrate to help aid in biological filtration. Under-gravel filters are very-well liked because they are fairly inexpensive and rely on either an air pump or powerhead to function. Under-gravel filters are primarily biological filters, so you will still need to add mechanical and chemical filtration to the aquarium as well. The only downfall about under-gravel filtration is that you are only limited to certain substrates. Some under-gravel filters get clogged very easily using soil or sand as substrate. So the main substrate you will be using will be “gravel”.

Undergravel filter
Under-gravel filter, photo by swisscath

Hang on Back (HOB) Power Filters

Hang on Back (HOB) Power filters are filters you are going to want to go with when you are dealing with fish tanks that are 10-40 gallons big. HOB Power filters are probably the most widely used aquarium filters due to their recent improvements in biological filtration, as well as their ease of use. Before recent times, biological filtration was very poor and was not really present in power filters. However, with the newer models, biological filter pads or bio-wheels are featured to aid in providing extra pollution removal.

Hang on Back (HOB) Power filter, photo by IVANDIAZ31

Canister Filters

Canister Filters are filters that you are going to want to go with when you are dealing with fish tanks that are 50 + gallons. Canister filters provide excellent mechanical, chemical, and biological filtration for larger aquariums. Compared to power filters, canister filters require slightly more effort to set up and maintain. But unlike hang on tank filters, canister filters can usually go several months without maintenance of any kind. Canister filters are virtually silent and use very little electricity. The magnetic impeller motors are extremely reliable and can last for well over a decade. This type of filter may be somewhat costly, but is well worth it in the long-run.

Canister Filter, photo by parezc

Wet/Dry Filters

Wet/dry filters are filters that you are going to want to go with when you are dealing with salt-water tanks of any size or even freshwater tanks that are in need of high biological filtration. These types of filters provide the best in biological filtration, better than any other filter out there. These filters are called wet/dry filters because the biological filter media is exposed to both aquarium water (wet) and a significant amount of air (dry). Water is pulled into the filter and poured over non submerged filter media such as bio balls, which creates maximum air contact for nitrifying bacteria to thrive. These filters are placed under the tank or close to the tank and requires special plumbing as well as a separate pump. Having a  pump too strong can cause overflow to occur, so make sure to get a pump that your wet/dry filter can handle.

Wet/Dry Filter
Wet/Dry Filter, photo by Doriath



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