Aquarium Filters

What are Aquarium Filters?

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

Types of Filtration

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

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

To decide which type of filter your aquarium needs, you’ll need to understand the different types of filtration that the filters can do.

Like the aquatic environment in the wild, your fish tank 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 waste 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 remove dissolved chemicals from the water. 

Biological Filtration

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

Types of Aquarium Filters

Before selecting the aquarium filter you’ll need to understand the needs of your fish and plants that you’ll have inside your 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. All of these factors should be evaluated before deciding which aquarium filter to buy.

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, use a box to house the filter parts. Using a box makes it possible to add different types of filter elements inside the box. Box filters are mounted to the side 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 water up into the filter. The air pumps make 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 you should have no problems adding 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 Filters

This aquarium filter has three parts – a sponge filter submerged inside your aquarium, 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. 

The sponge filter works by using an air pump to push water through a tube to the hollow space inside the filter. The air exiting the tube creates air bubbles that creates negative pressure inside of the filter that creates suction to pull water through the sponge filter. Mechanical filtration happens as water passes through the sponge walls, 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 tap 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 aquariums. They don’t create a noticeable current, making it easier for small fish to move around inside your aquarium. Another advantage is that they can be run on battery-operated air pumps. Battery power 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 your aquarium. These are one of the most commonly used filters for larger 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 water from 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 by adding or changing the filter pad. HOB filters are also easy to clean and maintain. Replacement pads can be ordered online and replaced 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

Canister Filters

Canister aquarium filters are powerful filters that are able to do all three types of filtration just like the HOB filters. They are housed in a plastic container that is kept outside the tank. Because they are outside of your aquarium it means that they don’t take up space inside your aquarium, and can even be hidden. 

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 water through them. This makes them ideal for medium to large fish tanks (more than 40 gallons) and for cleaning a lot of waste. Like the HOB filters, these also have several trays that the water passes through to get cleaned. It is also possible to add a bio-wheel to the canister filter. The bio-wheel will help enhance the biofiltration in your filter. 

These aquarium filters are efficient at cleaning a lot of water and don’t take up any space inside the tank. They are very good for saltwater tanks because 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 need 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 a mechanical filter 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. The filter takes the free-floating substances, along with the water which then gets filtered while passing through the plate filter. UGF filters are efficient because they have 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. Because they are submerged below the substrate it’s not easy to take the filter out when they become clogged. UGF filters are not recommended for fish tanks with living plants because 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 

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 create 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. Fluidized bed filters are not good at providing chemical filtration because they don’t 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 don’t come with air or water pumps and they will need to be purchased separately. Because they need more pieces they can be 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