Aquarium Filter: The Complete Guide to Aquarium Filtration

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An aquarium filtration system is an important component of a healthy fish tank. An efficient aquarium filter will help maintain good water quality in both freshwater and saltwater aquariums. They can help tremendously in maintaining water parameters in between regular water changes.

Without a filtration system, you would probably be required to do a lot more water changes, and only be able to stock a very limited number of fish in your aquarium. An aquarium filter is essential for almost every tank setup with live fish. There are many types of filtration systems, and each serves a different purpose.

Aquarium Filter Guide
Biological filtration is an important component of aquarium filters

How does an Aquarium Filter Work?

While most people who own fish know how important filtration is, the actual mechanics of how aquarium filters work may be unclear.

An aquarium filter works by pushing water through various types of filtration media. The main types of filtration media used are mechanical filters, biological filters, and chemical filters. Each filtration media has their own specific purpose. Mechanical filters physically traps large particles in the water by pushing water through floss or filter materials. Next, biological filters create a suitable environment for beneficial bacteria to thrive in. In other words, they are helping complete the nitrogen cycle in the aquarium. Lastly, chemical filtration is achieved by submerging select materials in the aquarium water for their desired effect. For example, activated compound is often used to extract dissolved waste in the water.

Each filtration type is described in detail below.

Aquarium Filtration Media

Mechanical Filtration

A mechanical filtration in an aquarium is achieved by passing water through a material, such as foam or polyester floss, which effectively blocks the passage of solid materials. These solid particles includes uneaten food, fish waste, and decaying plant material. Instead of allowing these particles to continuously float around the tank, they will be collected in the filtration system. However, mechanical filters are not designed to break down the waste and process it. The role of mechanical filtration is to simple collects the particles. This is why regular cleaning is required. Without regular maintenance, the filter may become clogged. If the particles start decaying or start dissolving back within the water, it will ultimately end up polluting the water it is filtering. In addition to cleaning, it is recommended to change the filter media occasionally as well.

Biological Filtration

A biological filtration in an aquarium is achieved by passing water over a medium rich in beneficial bacteria. The beneficial bacteria converts ammonia and nitrites into less dangerous nitrates. This is a part of the nitrogen cycle. Biological filtration enhances this process by increasing the surface area for these beneficial bacteria to grow on. Materials such as ceramic rings and bio balls are commonly used.

Biological filtration is considered the most important type of filtration in an aquarium. Compared to fish living in their natural habitat, fish in an aquarium is often living in a compact space, with a higher density of fish per gallon of water. Live fish constantly produce waste in the form of ammonia and nitrites. If the concentration of ammonia and nitrites is too high, it can damage the internal organs of the fish. If the fish are exposed to high concentration of these compounds over an extended period, they can die. Biological filtration systems help process these harmful compounds into nitrates, which are less harmful to the fish. Once converted to nitrates, it can be utilized by plants as fertilizers as well.

Biological filtration allows the aquarists to employ nature’s nitrogen cycle and break down ammonia into relatively less toxic nitrogen compounds.

Aquarium of the Pacific

One vital component of biological filtration is oxygen. Since the beneficial bacteria are aerobic, biological filtration can only be achieved if the water surrounding the filter medium is rich in oxygen. It is important to make sure that the filter media Is agitated with good water flow. If the filter media becomes clogged with debris over time, it can create an anaerobic environment. This will result in less beneficial bacteria, making the biological filter less efficient. At this point, the filter should be gently rinsed with old tank water. Washing the filter with tap water should be avoided since the chlorine could kill off the beneficial bacteria living on the filter.

Chemical Filtration

A chemical filtration in an aquarium is achieved by passing water through a medium, such as activated carbon or zeolite, which extracts dissolved waste and compounds in the water. Since mechanical filters are hardly effective against waste that has dissolved into the water, chemical filtration can be useful. Activated carbon can help remove chlorine and chloramine, dissolved proteins, tannins from bogwood, and bad odor. Zeolite effectively removes ammonia from the water.

It is important to keep in mind that chemical filtration requires regular maintenance as the filter medium can become ineffective over time. In addition, after the filter medium absorbs the harmful chemicals, it can start to release it back into the water over time. Therefore, the medium should be replaced regularly.

If the aquarium is being treated with a medication, the chemical filtration medium should be removed. If the filter medium will absorb the medication, which can cause the medication to be less effective.

Unlike mechanical and biological filtration, chemical filtration is considered optional by many fishkeepers. In fact, many plants can extract dissolved chemical waste, working in the capacity of a chemical filter. However, a chemical filter can be useful in the case of the spike in ammonia or other chemical. It can work as a buffer until the next water change or the root cause of the issue is dealt with.

Aquarium Filtration Explained by Fish Laboratory

Types of Aquarium Filters

The most common types of aquarium filters are sponge filter, power filter, and canister filter. The vast majority of aquariums today are equipped with either one of these filtration systems. Sponge filters are often used by smaller aquariums. They are a great method of biological filtration. Power filters are often used by small to medium sized aquariums. They are effective and easy to maintain. Both sponge filters and power filters are commonly used as filters for nano aquariums. Lastly, canister filters are equipped on many of the medium to larger sized aquariums. This is because they usually have a larger capacity than other types of aquarium filters.

There are other types of aquarium filters that are less common in the aquarium hobby today. For example, undergravel filters have were popular at some point in the hobby. However, with so many great alternatives, they have become less popular today.

Aquarium Sponge Filter

Sponge filters are the most simple and usually the most affordable type of aquarium filter. It consists of an air pump, airline tubing, and the sponge filter itself. As the air is pumped, and the air bubbles naturally rises to the surface, water is forced through the sponge material. Sponge filters can be installed in almost any tank, but they are most suitable for smaller tanks up to 20 gallons. However, there are larger units designed for larger tanks. In addition, multiple units can be installed in a tank in order to handle the bio load of the entire tank as well. Since fish are less likely to sucked into a sponge filter, they are a popular choice for fry tanks as well.

Aquarium Sponge Filter

As the water passes through the sponge material, small particles are captured by the sponge, which enables some mechanical filtration. With this simple design, sponge filters may not be able to capture larger particles in the water. However, sponge filters are primarily used as a means of biological filtration rather than mechanical filtration. The sponge is a great medium to house beneficial bacteria.

Due to its simple design, sponge filters are easy to install and maintain. Once it is connected to an airline tube and an air pump, the sponge filter can be installed almost anywhere in the tank. Simply drop the sponge filter in a corner or stick it to the glass wall if it comes with a suction cup. For maintenance, gently squeeze and rinse the sponge in old tank water. The sponge should be replaced as needed.

Aquarium Sponge Filter: Pros and Cons #shorts

Aquarium Power Filter

Power filters, also known as hang-on-back filters, are a type of aquarium filter that draw water from the tank and filters it through a filter chamber. The lift tube, filter chamber, and pump are all combined in one system. Simply hang the power filter on the edge of the tank, insert a filter cartridge in the filter chamber, and plug in the power. As the water passes through the filter cartridge and debris in the water will be collected, the water will be mechanically filtered. Most filter cartridges has a pouch that allows you to insert material for chemical filtration as needed, such as activated carbon. This will allow you to remove toxic impurities and odors from the water. Lastly, as the water is passes through the filter chamber, the filter medium is constantly oxygenated, allowing beneficial bacteria to grow on it. This will aid in the biological filtration. While power filters come in a relatively compact size, the function that it can perform is extensive. Therefore, they have become one of the most popular type of filters for medium to size aquariums ranging from 10-70 gallons. While less common, there are power filters with gentle output that can be installed in small betta tanks under 5 gallons as well.

Aquarium Power Filter

Power filters are not only easy to install, but they are also easy to maintain as well. When the filter becomes clogged, simply rinse it out in old tap water. Occasionally, the filter cartridge will need to be replaced. This is a simple task as well, since the manufacturers of the power filters sell replacement filter cartridges. Simply pull out the old filter cartridge, and slip in the new one. There is no need to disassemble the entire filter.

Internal power filters are designed to be installed inside the aquarium. These power filters work in the same manner as a hang-on-back filters, which are considered external power filters. However, one the difference is that internal power filters are installed inside the tank and there is no lift tube. The intake pulls the water directly into the filter chamber. Once the water passes through the filter, it water is pushed out of the output, just like a hang-on-back filter. Both internal power filters and hang-on-back filters work great. Since there is very little difference in functionality, it is a matter of preference for the most part. Some people prefer to maximize the tank capacity with a hang-on-back external power filter. Others prefer to contain the components with an internal power filter. Once functional difference between the two filters is that some internal power filters allows you to install the filter at a lower part of the tank. Instead of hanging the internal filter on the edge of the tank with a hook, you can install the filter on the glass wall with a suction cup. This can be a useful function if you wish to keep the water level in your aquarium shallow. You may wish to keep the water level low for some fish and other pets such as turtles, frogs, and crabs.

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Aquarium Canister Filter

A canister filters is a type of external aquarium filter that is designed to be placed below an aquarium, connected by tubes. A water intake is installed in the aquarium, and the water is pulled into the canister, which holds the filtration media. Once the water reaches the canister, it passes through a series of chambers, which includes mechanical, biological, and chemical filtration media. After the water passes through the filtration media, it goes back up to the aquarium through a tube, and it is returned into the aquarium through an output. Usually a pump is installed at the top of the sealed canister that allows water to flow through the filter media. Canister filters are designed for larger aquariums, ranging from approximately 50-200 gallons.

Aquarium Canister Filter

Canister filters have many advantages and some disadvantages to consider.

One advantage of the canister filter is that it can hold a lot of filtration media. You can fill the canister filter with different types of media. For mechanical filtration, you can add filter floss and sponge material. For biological filtration, ceramic rings and lava rocks can be added inside the filter. If you wish to have chemical filtration, the media of choice such as activated charcoal can be added to the filter. Since the filter chamber of a canister filter is usually much larger than a power filter, this allows more rooms for customization.

A second advantage of a canister filter is that it provide good water flow. First, the higher power of the larger system will create a stronger water flow. Next, the intake and the output can be positioned separately. For maximum flow and efficiency, the intake and output can be placed on opposite ends of the tank. This will prevent it from filtering only the water near the filter over and over again, leaving the water on the other side of the tank unfiltered.

A third advantage of a canister filter is that they are not very noticeable. Since they are designed to be installed below an aquarium, they can easily be hidden from view. The only visible component of the canister filter will be the intake and output on the corners of the aquarium. They are usually much quieter than other types of filtration systems.

The fourth advantage of canister filter is that some canister filters come equipped with UV sterilizers, or UV filters. The UV sterilizer have the ability to purify the aquarium water of some waterborne algae, bacteria, and parasites. They are useful if you have green water due to algae or white water due to bacteria bloom. Parasites such as ich and flukes can be destroyed by UV light.

However, UV sterilizers will not be able to affect algae that are attached on the surface, since it will not pass through the filtration system. Keep in mind that UV sterilization is different from mechanical, biological, or chemical filtration.

One disadvantage of a canister filter is that they can be time consuming to maintain. First, the hoses must be disconnected and removed from the bottom of the tank. Next, the filtration media must be removed and rinsed, then placed back together. 

Another disadvantage of a canister filter is the potential for leakage. Since the filtration system is placed outside of the aquarium, and it is connected by tubes, water could leak out. The connection points between the tubes and the canister filter is usually where the leak occurs. The best way to prevent leaks is to ensure all components are installed and sealed properly, and parts are replaced when needed. If the canister filter is placed on top of a plastic tray, it can help detect a leakage in its early stages.

Keep in mind that canister filters are one of the more expensive types of filters. For example, compared to power filters of the same capacity, canister filters can be more than triple the cost.

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Aquarium Undergravel Filter

Undergravel filter is a type of aquarium filter that is designed allow water to flow through the aquarium gravel. When the water flows through the gravel, it delivers the necessary oxygen to allow beneficial bacteria to grow on the aquarium gravel, enhancing its biological filtration capabilities.

In order to install an undergravel filter, lay the undergravel grid on the very bottom of the tank. This grid will provide an open chamber below the aquarium gravel. Next, connect the undergravel grid to an uplift tube. When the water flows up the tube, this will force the water to flow through the aquarium gravel, into the open chamber. Lastly, in order to create the water to flow up the tube, use a powerhead or an airstone.

While undergravel filters can be useful, they can be disadvantageous in a few aspects.

Since the undergravel filter must be installed below the gravel, it must be installed in the very beginning when you setup your tank. Otherwise, you will be required to completely overhaul your aquarium. Installation can also be difficult, if the undergravel filter does not fit your aquarium properly.

Debris can collect in the undergravel grid. While some of the debris can be siphoned out during water changes, this can be a difficult task. Even then, a good portion of the debris will always build up under the gravel. Unfortunately, if the undergravel grid becomes too clogged, the filter will become inefficient. In addition, if you wish to completely remove all of the debris, the aquarium gravel will need to be removed as well.

There is very limited potential for mechanical and chemical filtration. A well-functioning undergravel filter will be able to house lots of beneficial bacteria, and this is important for biological filtration. However, there are limited options for mechanical and chemical filtration. Some undergravel filters will come equipped with space to add filter media in the uplift tube. However, these options are very limited.

While undergravel filters were popular at some point in the aquarium hobby, they are becoming less common today.


Which aquarium filter is the best?

The best aquarium filters available on the market is the Fluval canister filters. They are quite, capable, and versatile.

If you own a large aquarium, the Fluval FX series is recommended. The Fluval FX4 is able to handle up to a 250 gallon aquarium. The Fluval FX6 is able to handle up to a 400 gallon aquarium. Both are known for its strength and durability. One of the best feature of these models is the drain on the base of the unit. This allow you to perform water changes directly through the filter for efficiency.

For aquariums under 100 gallons, the Fluval 07 series is a great option. These models are quiet and efficient, so they are suitable for many home aquariums. It comes with a wide selection of filter media as well.

Keep in mind that canister filters are usually more expensive than other types of filtration systems. As a top of the line product, Fluval products will cost you much more than the average aquarium filter. If you are looking for a budget friendly option, we recommend a good power filter.

One of the best aquarium power filter we know is the Marineland Emperor Pro filter. These filters are capable and reliable. While power filters are sometimes a bit noisy, these models are designed for a quiet operation. In addition, these filters come with a bio-wheel that spin as the water flows through. This will allow additional surface area for the beneficial bacteria to grow and aid in biological filtration.

How often should I clean my aquarium filter?

Aquarium filters should be cleaned every month, or as needed. If you have fish producing lots of waste, you may need to clean it more often. On the other hand, if there is only a few small fish in the tank, there may be no need to clean it. The important thing is to check the filter regularly to make sure that it is functioning properly. If the filter media becomes too clogged, it will become inefficient. Debris will be captured by the filter floss and other mechanical filtration media first, but once it’s clogged, it will hinder its biological and chemical filtration capabilities.  Simply rinse the filter in old tank water. Avoid rinsing in tap water since the chlorine can kill the beneficial bacteria on the filter.

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When should I change my aquarium filter?

Aquarium filters should be changed every month, or as needed. If there is lots of debris caught in the filters, simply rinse it in old tank water in a separate bucket to remove the large particles. If the filter is clogged, give it a light squeeze. If the filter is still clogged after it is cleaned, it is time to change the filter media. The mechanical filtration, such as the filter floss, can be changed relatively frequently. However, the biological filtration should not be changed if unless it is absolutely necessary. Some biological filtration media, such as the bio balls, are designed to never require replacement. If the biological filtration media is replaced, it should not be replaced at the same time the mechanical filtration media is replaced. Change the filter media gradually, in order to allow some time for the bacteria to grow on the new media. This will cause less stress on tank.

How much time should the aquarium filter run?

An aquarium filter should be running 24 hours a day, even at night. The filtration system in an aquarium is not only responsible for keeping the water clear. In fact, they are responsible for creating the necessary water flow as well, which helps deliver oxygen throughout the tank. The oxygen is important for the fish and the beneficial bacteria in the tank. If the filter is turned off, and the aerated water is no longer delivered to the filters and gravel layer of the aquarium, beneficial bacteria will start to suffer. Even if the filter is turned off for only a few hours, beneficial bacteria can start to die off. Without the beneficial bacteria, ammonia levels in your aquarium can spike up, ultimately harming the fish.

Why is my aquarium filter so loud?

There are multiple reasons why your aquarium filter could be loud.

If there is a dirt or a clog in your aquarium filter, it could be making a grinding noise. If a clog is suspected, turn off the filter and remove the debris that is stuck.

If too much water flow is causing a splashing noise, the flow rate may need to be adjusted. The flow direction or angle may need to be adjusted as well. If the output is above the water level, it may create a waterfall effect. This will create a splashing noise. Making sure that the output is under the water level may solve your issues. You may be able to dampen the noise with a baffle as well.

If the impeller is getting stuck, try using a non-toxic lubricant, such as Vaseline. Use just a little lubricant to coat the shaft of the impeller.

Air pumps can be noisy, if it is vibrating against a hard surface. Consider placing the pump on a surface that will absorb the vibrations, such as a rubber mat.

Most filtration systems operate with a certain level of noise. However, there are some products that are manufactured to produce less noise than others.

Air pumps are known to operate with a humming noise, as it vibrates. Especially when the flow rate is maximized, the noise can increase significantly. Luckily, there are air pumps that operate very quietly.

The quietest air pump we know is the Eheim Air100. This air pump is designed for a very quiet operation.

Power filters also operate with a certain level of noise. However, MarineLand manufactures relatively quiet power filters.

The quietest power filter we know is the MarineLand Emperor PRO filter. This model is exceptionally quiet since the motor is submerged and it is equipped with a motor dampener specifically to reduce noise.

Most canister filters operate at a lower level of noise than other types of filters. The Fluval 07 series canister filters are exceptionally quiet.

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