Aquarium Filter - Fish Tank Filter

Updated August 12, 2019
Author: Mike - FishLore Admin
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Your aquarium filter helps increase the quality of the water in your fish tank. Most think of mechanical filtration when it comes to aquarium filters but as you will soon see, there are some other fish filter types that you need to know about.

Mechanical, Biological & Chemical Aquarium Filters

There are three types of aquarium filtration:
  1. Mechanical Filtration
  2. Biological Filtration
  3. Chemical Filtration

Mechanical Aquarium Filters

Mechanical filtration removes the free floating particles from the aquarium water. The siphoning action of a power filter that hangs on the back of an aquarium does a decent job of this type of filtration.

Biological Aquarium Filters

Biological filtration is the most important aquarium filtration type because it deals with the growing of the good bacteria in your aquarium filter. The good bacteria is the bacteria that converts ammonia to nitrite and then converts nitrite into nitrates. This establishment of bacteria is essential to your success with keeping tropical fish. For more information please read about the Nitrogen Cycle.

Ammonia   ->   Nitrite   ->   Nitrate

Chemical Aquarium Filtration

Chemical filtration involves removing the dissolved wastes from the aquarium water. Often times this is accomplished through the use of activated carbon in the aquarium filter. Activated carbon can also help to reduce odors. Many people dislike using carbon in their tanks due to the fact that the carbon is useful for only a short period and then must be replaced. If it doesn't get replaced in a timely manner the very wastes that it removed can be released from the carbon back into the aquarium.

Zeolites can also be used in chemical filtration. Zeolite removes ammonia from your aquarium water and can be a fish life saver if you have high ammonia levels. Many first time fish keepers mistakenly add too many fish to a new aquarium before it has cycled and experience the disappointing loss of their fish. Using zeolite during the cycling process in your aquarium filter can help prevent this from happening but it has the side effect of lengthening the time it takes to complete the aquarium nitrogen cycle.

Types of Aquarium Fish Filters

Corner Filter

The corner filter sits inside the aquarium in one of the corners or even sticks on to the glass. It is very low-tech but a corner aquarium filter can be used successfully for mechanical, chemical and biological filtration. The key is not to change out the entire filter material when performing maintenance. Only change out the carbon and part of the filter material. Corner filters require frequent maintenance and are only used in very small tanks these days if at all.

Undergravel Filter (UGF)

Undergravel filters are commonly found with beginner's aquarium kits and the undergravel filter has been around for a long time. Undergravel aquarium filters can provide good mechanical filtration because it forces the water down through the aquarium gravel where particles are trapped. You can then use an aquarium vaccum to clean the detritus.

Biological filtration occurs in the gravel because of the slow flow of water through it. The water is then pushed up through the uplift tubes in the back of the tank where chemical filtration takes place with the activated carbon in the top of the tubes.

The problem with this type of aquarium filter stems from the fact that it can be difficult to thoroughly vacuum the gravel and harmful gas pockets can form under the gravel plates thereby harming your tropical fish. I personally don't use undergravel filters because of this reason. Many long time fish keepers still use the undergravel filter and swear by it. If you do use an undergravel filter try to regularly vacuum your gravel to prevent the harmful gasses from forming.

Sponge Filter

Sponge Filter Sponge filters can provide a cheap and effective form of biological filtration. Water flows through the airlift tube allowing a colony of beneficial bacteria to grow in the sponge. There is no chemical filtration with this method and the mechanical filtration is very weak. You must do frequent water changes if this is your only form of filtration. Many breeders use the sponge filter in conjunction with a bare bottom tank. After feeding their young fish they will siphon any remaining food to prevent the water quality from detiorating. Frequent water changes are performed because it aids in the rapid growth of the young fish. Fish breeders don't have to worry about mechanical or chemical filtration as much because they are performing frequent water changes.

power filter

The power filter is probably the most popular filter type for a variety of reasons. They are easy to use and clean and they can be an effective means of mechanical, chemical and biological filtration! The drawback to using power filters is that it is very inefficient because of its design. The intake tube for the dirty aquarium water is directly below the lip of the outflowing filtered water. Does this make any sense? Not to me either.

More aquarium kits come with a power filter than any other type of aquarium filter. Try to get a power filter that contains two filter media slots. With two filter slots you can change out one side of the filter and then a few weeks later change out the other side. If you change out the entire set of media cartridges at once you run the risk of having to re-cycle or mini-cycle because you've tossed out much of the beneficial bacteria.

Canister Filter

Canister filters are on the higher end of the price scale but they are pricey for a reason. They work very well. Often there are multiple trays for a canister filter with each tray providing a type of filtration. The first tray could be a sponge that filters (mechanical and biological) the large particles. The second tray could be filled with zeolite that removes ammonia from the water (chemical). The third tray could be activated carbon which would further filter (chemical) the water. Most canister filters push the water from the bottom of the canister to the top but some work just the opposite. Find out which way yours works to get the most out of the canister filter. This is our personal choice of aquarium filter on most of our freshwater fish tanks.

Protein Skimmer

Protein skimmer models come in a few different styles. There are those made for in tank use (Visi Jet PS, Slim Skim Protein Skimmer), protein skimmers that hang on the back of the tank and those designed for use in a sump.

Those desiged for in tank use are usually less desirable because they don't seem to work as well as the other types. Try to get one that hangs on the back of the tank such as the AquaC Remora Protein Skimmer or one for your sump. Also, make sure that you can easily get to and remove the collection cup for daily or weekly cleaning.

This piece of equipment is usually very pricey but it is a critical piece of equipment for saltwater aquarium beginners nonetheless. They are virtually useless in freshwater tanks.

In saltwater tanks, the skimmer will remove dissolved organic material from the water and anyone who has used one can tell you about the smelly brown gunk that gets pulled from the water. In the past, saltwater aquarium keepers would sometimes experience a complete die off of the fish in their tanks. Many believe that it was due to the amount of dissolved organics in the water and by using a protein skimmer they have drastically reduced the chances of this happening. Skimmers completely remove proteins into a collection cup that can be emptied on a regular basis before they break down in the aquarium leading to algae blooms and DOC buildup. Protein skimmers also help increase the dissolved oxygen levels in your saltwater aquarium.

Since this is an expensive piece of equipment you will want to shop around and research the various models out there. It's been our experience that you usually get what you pay for when it comes to skimmers. Get the biggest and best rated skimmer that you can afford.


A powerhead is considered part of the filtration system? Yes, indeed. In freshwater aquariums, power heads are used for water movement as well as in conjunction with an undergravel filter system. If you're running a system where air stones drive the water flow in your undergravel filter, consider using a power head in one of the uplift tubes. The power head should help generate much better flow through the UGF, resulting in a more efficient UGF. Many come with a tube that is connected to the power head that hangs on the outside of the tank with an air flow valve. This allows you to mix air with the water being pushed out of the power head. That can help increase surface agitation and aeration in your tank.

Saltwater hobbyists frequently use multiple power heads situated in a way that allows them to control the flow of the water in the tank or even better, to create turbulent water flows. Saltwater tanks usually require more water movement than freshwater tanks. Constant water movement prevents dead zones in a tank and keeps uneaten food suspended in the water column so that the fish can eat it or the mechanical filtration and/or protein skimmer can get rid of it.


A refugium is an external tank, usually smaller, that is used to house smaller fish and invertebrates for cultivation and/or feeding the fish in the display tank. It can be connected to the main tank and is sometimes apart of or separate from the sump. You can even get a hang on the back of the tank type refugiums or DIY a power filter to use as a refugium. See the DIY refugium setup for more information. A refugium provides isolation for those more delicate specimens that can easily and quickly become food for the larger fish in the display tank.

Aquarium Sump

A sump is also an external tank but one that has water lines connected to the display tank. They can be any size but are often smaller and placed hidden below the main tank in the cabinetry. Sumps can provide many benefits for you. They can help with nutrient export by allowing certain macro algae types (chaetomorpha, for example) to grow uninterrupted from grazing by your herbivores in the display tank. Sumps also increase the total amount of water in the system. For instance, if your aquarium is 55 gallons and your sump is 20 gallons, you essentially have a 75 gallon tank.

This extra tank also gives you the ability to hide ugly equipment (like filters and protein skimmers) that could diminish the look of the display tank. Many saltwater hobbyists add any saltwater supplements to the sump instead of the main tank. Supplements such as Iodine, strontium, kalkwasser (lime water) dosing systems and others are often placed into or connected to the sump. Is a sump absolutely necessary for a saltwater aquarium? No, they are not mandatory but they can definitely help in keeping your system (water parameters) stable and they can help hide equipment under the display in the cabinet.

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