Aquarium filter

What are Aquarium Filters?

Aquarium Filters are devices that remove waste from your fish tank. The waste in your fish tank is generated from fish, decaying organic matter, excess food and plants present in the water. It is important to remove their toxic by-products from your aquarium to provide a clean living environment for your fish. If the waste is not removed the water will become toxic and eventually kill your fish. This is why it is important to install a filter for your aquarium.

Types of Filtration

Several types of aquarium filters are available in the market with each one having its own pros and cons. The filter required by your aquarium set up will depend upon three major factors.

  • Number of fish in the tank
  • Size of the tank
  • Plants in the tank

To decide which type of filter your aquarium needs, first you should understand the different types of filtration that are carried out by the filters.

Like the aquatic environment in the wild, your aquarium will generate three types of waste – solid, biological and chemical. In line with this, there are 3 types of filtration that aquarium filters perform –

Mechanical filtration  

This involves removing free-floating solid wastes like fish poop and excess food from the water. It is just a basic filtration process as it does not remove the chemical and biological matter from the water.

Chemical Filtration

There are many invisible and dissolved compounds in the tank that are not removed by mechanical filters. These are removed by adding additives to the water like activated carbon that helps clean the water of dissolved chemicals. 

Biological Filtration

The presence of high levels of compounds like ammonia and nitrites in the tank can be toxic for the fish. Biological filtration uses beneficial bacteria to break down the ammonia and nitrites to less toxic nitrate compounds. This prevents your fish from feeling stressed by cleaning the water. This is the most important filtration process in home aquariums.

Types of Aquarium Filters

Now that you have an idea about the different types of filtration processes you can select an aquarium filter that will work best for your fish tank. Before selecting the aquarium filter you should understand the requirements of the fish and plant species that you will be keeping inside the tank. The size and type of fish tank – saltwater or freshwater, also need to be considered. Some filters like sponge filters may not be as effective in cleaning large water tanks. So, you should evaluate all these factors before deciding which aquarium filter to buy.

Aquarium filter media

Box Filters

These are the most basic and earliest aquarium filters used for fish tanks. They are also known as corner or internal filters. Box filters, as the name suggests uses a box to house the filter parts. This makes it possible to add different types of filter elements inside the box. Box filters stick to the sides of the tank and are best suited for tanks 20-gallons or less. It works with the principle of air-lift. Air pumps or air stones create bubbles that push the water up into the filter. This makes the water flow to the sides or bottom vents of the filter. The air bubbles also help improve the chemical and biological filtration process.

The advantage of box filters is that they are inexpensive and very easy to use. Even if you are a new aquarium owner then you can easily add this to your aquarium. These aquarium filters will clean your aquarium’s water, but not very fast. They are also known for not being that efficient.

Operation and Maintenance Level – Beginner

Cost – $6 to $25

sponge filter

Sponge Filters

This aquarium filter has three parts – a sponge filter submerged inside the tank, an air pump that sits outside and an air tube that connects both. Some come with just a standalone sponge filter and an air pump will have to be purchased separately. It works by using an air pump to push the water through the tube to the hollow space inside the filter. This generates air bubbles that further help force the water inside the tank and pass through the filter. As the water passes through the sponge walls mechanical filtration occurs, trapping particles from the water in the filter. 

The sponge inside the filter allows beneficial bacteria to grow. Because of the bacteria on the sponge, you should only use water from your aquarium when cleaning the sponge. Using sink water may kill the beneficial bacteria that is growing on the sponge.

Sponge aquarium filters are cheap and one of the easiest filters to use for fish tanks. It does not create a noticeable current which helps small fish move around easily inside the tank. Another advantage is that they can be run by battery-operated air pumps. This will keep the filter running even if there is a power outage.  The disadvantages of sponge filters are that they do not provide chemical filtration and tend to become clogged over time.

Operation and Maintenance Level – Beginner

Cost – $6 to $25 (only for sponge filter unit)

Hang-on-Back Filters

Hang-on-Back aquarium filters or HOB filters, as the name suggests hang on the back of the tanks. These are one of the most commonly used filters for fish tanks. They are attached to the top rim of the tank with the filter box hanging outside and the intake tube is lowered inside the tank. The intake tube siphons the water inside the tank, passing it through the filters and then pouring the water back into the tank. A power motor inside the HOB filter helps drive the flow of water. Most HOB filters come with all the three filter layers – mechanical, chemical and biological. 

The filter media can be customized easily by adding or changing the filter pad. They are also easy to clean and maintain. You can order replacement pads online and replace them within minutes. The downside to HOB filters is that they can be noisy. This can be irritating if you have the fish tank in a room where someone sleeps or works. They also need a constant power source to work, so power outages can be a concern.

Operation and Maintenance Level – Medium

Cost – $10 to $150

hang on back filter
canister filter

Canister Filters

Canister aquarium filters are powerful filters that just like the HOB filters perform all three types of filtration. They are housed in a plastic container that is placed outside the tank. Because they are outside of your aquarium it means that they don’t take up space inside your aquarium. 

The aquarium filter has two openings, one for the tank water to go in and the other for the filtered water to come out. Two tubes, attached to these openings are submerged inside the tank. The canister filters use pressure to force the water through them. This makes them ideal for medium to large fish tanks (up to 40 gallons) and for cleaning a lot of waste. Like the HOB filters, these also have several trays through which the water passes and gets cleaned. It is also possible to add a bio-wheel to the canister filter. This will help enhance the biofiltration of water. 

These aquarium filters are efficient at cleaning the water and do not take much space inside the tank. They are very good for saltwater tanks as they take care of all three types of filtration. The downside to these filters is that they are expensive and cleaning them requires more effort than sponge or box filters. To clean them the entire container will have to be dismantled and then the individual trays will have to be cleaned. 

Operation and Maintenance Level – Medium to Advanced

Cost – $40 to $150 

Under Gravel Filters

The design of these aquarium filters are a little different from the other filters mentioned in the list but they have also been around for a long time. Under Gravel Filters (UGF) consists of a plate filter that is placed below the substrate. The plate filter acts as the mechanical while the substrate acts as a biological filter, promoting the growth of beneficial bacteria. 

A UGF uses an air pump to force the water through the substrate and the plate filter. This takes the free-floating substances, along with the water which then gets filtered while passing through the plate filter. UGF filters are efficient as they provide a large surface area for the filter media. If you want to filter chemicals you can add an activated carbon section to the tubing for most of these.

They are easy to install and can be relatively inexpensive. The downside to these filters is that maintaining them can be rather time intensive. Since they are submerged below the substrate it is not easy to take the filter out when they become clogged. UGF filters are not recommended for fish tanks with living plants as they often become clogged because of the plant roots.

These filters were much more popular +30 years ago. Now you will mostly only find them in smaller aquariums or aquariums for children. The main reason why they’re in smaller aquariums is because there isn’t much space for a sponge filter. The cost of more efficient aquarium filters are quite high when there is only 5 gallons of water to filter.

Operation and Maintenance Level – Medium 

Cost – $8 to $80 

under gravel filter
Fluidized Bed Filters

Fluidized Bed Filters

These are newer aquarium filters that are very efficient at biological filtration. Depending on the one you choose you can get one that hangs inside of your aquarium, or an external upright model. They are available in either a canister or cylinder style. One nice thing about the external filters is that they don’t take up any space within your aquarium. They handle all the filtration and pump the cleaned water back inside. 

They come in a number of different sizes, and DIY filters are also quite popular. You can get them large or small enough to handle most aquariums. These filters work by pushing the water into the filter through a water pump that is attached to the filter. Fluidized Bed Filters use sand or small plastic media to clean the water. These remain suspended inside the filter that helps provide a large surface area for beneficial bacteria to grow. 

They are often used as an extended filter to enhance the biological filtration process of aquariums. They are not good at providing chemical filtration because they do not contain activated carbon or charcoal filters. The level of mechanical filtration capability depends on the filter model you get. Some DIY and commercial models will have a sponge attached that can be removed for cleaning. Most of the Fluidized Bed Filters do not come with air or water pumps and they will need to be purchased separately. This can make them a more expensive filtration option than a sponge, but still cheaper than a canister filter that they can outperform.

Operation and Maintenance Level – Medium 

Cost – $50 to $150 

Depending on your aquarium filter needs, you have several different options at a few different price points. The most popular aquarium filter by far is the sponge filter and for most average size to large size aquariums this will work perfectly, not only to filter particulates from the water, but neutralize harmful chemicals, and also aerate the water.  If you have a smaller aquarium than an under gravel filter might work best if your aquarium is too small for a sponge filter.  Canister and HOB’s will work best for the larger aquariums that don’t want multiple sponge filters taking up space within their aquarium.

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