Beginner's Guide to Aquarium Filters and Types of Filtration

A filter, or the “heart” of the tank as we like to call it, is a crucial part of a fully functional and balanced tank. Like with many other things in the aquarium hobby, there is an overwhelming amount of brands, types, and sizes. What kind of filter is best for you and your tank? First, you will need to understand the basics in order to choose the right filter for your aquarium.

Why Does A Tank Need A Filter? 

The filter serves as the lifeblood of the tank, ensuring continuous water flow to prevent stagnation. Stagnant water creates an environment where harmful ammonia can accumulate, posing risks to the well-being of your plants, fish, and shrimp. Without proper water circulation, the oxygen levels in the tank become limited. In the absence of a filter or air stone, small tanks require frequent water changes and careful animal population management.

The movement of water plays a vital role in facilitating gas exchange and nutrient distribution throughout the tank, providing essential elements for the thriving life of your aquarium inhabitants. A well-functioning filter not only promotes cleanliness but also maintains a crystal-clear water column, offering the best possible view of your tank's beauty.

As discussed in our earlier blog on the nitrogen cycle (Here), the filter acts as the primary habitat for beneficial bacteria. Preserving the population of these beneficial bacteria is of utmost importance for the health and prosperity of your planted aquarium and its inhabitants. Therefore, the filter holds immense value as crucial and indispensable equipment for aquascapers.

3 Different Types of Aquarium Filters

When it comes to aquarium filters, there are several types to consider. In this discussion, we will explore three common types: sponge filters, hang-on-back filters, and canister filters, each with its own advantages and disadvantages.

1. Sponge Filters

Sponge filters consist of a spongy material placed inside the tank, with the air pump located outside. The filter's suction, powered by the air pump, draws debris and detritus from the aquarium through the sponge. Sponge filters are the simplest and most straightforward type of filter available.

While some aquarists may be hesitant due to the visible sponge in the tank, they remain popular among experienced hobbyists.

These filters are well-suited for smaller aquariums and breeding tanks, providing gentle water movement without disturbing the fish. However, in larger tanks, sponge filters may not provide adequate water circulation throughout the entire tank.

2. Hang-on-Back Filters

Hang-on-back filters are the most commonly used filters in the hobby. As the name suggests, these filters hang on the edge of the tank, typically at the back. They function by pulling water from the tank through a pump, passing it through different sections of filtering media, and returning it to the tank via a spout.

Hang-on-back filters are known for their ease of cleaning and maintenance, making them suitable for all tank sizes. They are particularly favored by beginners, but experienced aquascapers also appreciate their convenience.

For larger tanks, you can even run two Hang-on-back filters for increased filtration capacity.


3. Canister Filters

Canister filters are renowned for their discreetness and high filtration power. These pump-driven filters are usually placed hidden underneath the tank, within the aquarium stand. The only visible parts are the return and outtake pipes, which can be swapped with glass or steel pipes for a more subtle appearance.

Canister filters are ideal for larger tanks, typically over 30 gallons, that house a significant number of livestock requiring robust filtration to maintain a healthy balance. Although canister filters offer excellent filtration capabilities, they are relatively more expensive and require higher maintenance compared to Hang-on-back filters and sponge filters.

Types of Filtration

To fully understand the components of a filtration system and the significance of having a filter in your tank, let's delve into the different types of filtration:

1. Mechanical Filtration

Mechanical filtration focuses on the removal of solid waste particles like fish waste, uneaten food, and decaying plant matter. This type of filtration employs media that physically traps and captures these particles as water passes through it. By effectively cleaning the tank and promoting water circulation, mechanical filtration aids in maintaining optimal water quality.

2. Biological Filtration

Biological filtration is specifically designed to eliminate biological waste, primarily excess ammonia, in the aquarium. Beneficial bacteria, residing in the filter media, play a crucial role in this process. These bacteria convert harmful ammonia into less toxic substances like nitrite and eventually nitrate through a process called the nitrogen cycle. Proper biological filtration is essential for establishing a balanced tank environment and ensuring the well-being of fish, shrimp, and plants.

3. Chemical Filtration

Chemical filtration targets the removal of dissolved waste substances, such as decaying organic matter or chemicals present in the water. Activated carbon is commonly utilized as a chemical filtration media. Its porous structure effectively adsorbs and traps these dissolved impurities, preventing them from discoloring the water and causing unpleasant odors. It is important to note that while activated carbon is beneficial for chemical filtration, it should be periodically replaced as it becomes saturated with contaminants.

Important Components Inside of a Filter

In addition to the wide variety of filter brands, shapes, and sizes, the components inside a filter can be equally extensive. Let's explore the main parts of a filter, including the filtering material, filter media, and activated carbon.

1. Filter Floss

Filter floss is a densely packed material made of polyester fibers, forming a sheet-like structure. As water passes through this compacted sheet, it effectively captures and removes small particles, providing mechanical filtration in the tank.

2. Filter Sponge

A filter sponge consists of a coarse pad placed before the filter floss. It helps trap larger particles, preventing clogging and enhancing the efficiency of mechanical filtration in the tank.

3. Media Rings / Bio Balls

Filter media, such as ceramic rings like Aquario Neo Media or bio balls like Seachem Matrix, provide a porous surface area for beneficial bacteria to thrive. These beneficial bacteria play a vital role in biological filtration, establishing a balanced nitrogen cycle and promoting water quality in the tank.

4. Activated Carbon

Activated carbon, an optional component, can be added to the filter to remove chemicals and other pollutants from the tank's water column. The pores of activated carbon trap these substances, but over time, the pores become clogged. Hence, regular replacement of activated carbon (around once a month) is necessary to maintain its effectiveness.

Hint: Keep in mind that activated carbon will also filter out fertilizers and medications. Therefore, it is advisable to remove the activated carbon before administering such substances.

Which Filter is Best for Your Tank?

Before purchasing a filter, there are a few important factors to consider.

First, determine who will be viewing the tank and the purpose of the tank. If it's a display tank aimed at showcasing your aquascape, a hang-on-back filter or canister filter would be the ideal choice. These filters are designed to be less visually obtrusive, allowing the focus to remain on the beauty of your aquascape. On the other hand, for a grow-out or breeding tank where aesthetics are less of a concern, a simple sponge filter can work effectively.

Flow rate is another crucial factor to keep in mind. Flow rate is measured in gallons per hour (GPH), indicating the volume of water passing through the filter within one hour. It is generally recommended to have a filter with a flow rate of at least 4-6 times the tank volume.

For example, a 20-gallon tank should have a filter with a flow rate of 80-120 GPH.

This ensures efficient filtration while avoiding excessive water current that may disturb the tank's inhabitants.

For larger aquariums, it may be necessary to use larger filters or multiple smaller filters to ensure adequate water circulation and filtration throughout the tank.

Filter Maintenance

While maintenance may not be the most enjoyable task, it is crucial to regularly maintain your tank and filter for optimal aquarium health.

The frequency of filter cleaning depends on factors such as the tank's population, filter size, and debris accumulation. To ensure a clean and functioning filter, it is recommended to establish a regular and consistent maintenance routine. Remember, even though the waste is filtered out of the water, it remains trapped in the filter system. Don't forget about it!

Mechanical filtering materials, such as filter floss and filter sponge, can be either replaced or rinsed off in a sink to remove accumulated debris and maintain their filtering efficiency.

Chemical filtration media, like activated carbon, should be replaced approximately once a month or every 4-6 weeks. Over time, the pores of activated carbon become saturated with absorbed chemicals, reducing its effectiveness in removing impurities.

When it comes to biological filtration media, it is crucial to handle it with care. Never rinse it off in a sink or replace it abruptly. This is because beneficial bacteria reside within the media, and exposing them to tap water containing chlorine can harm or kill these essential microorganisms. Disrupting the population of beneficial bacteria can lead to an unbalanced nitrogen cycle and potentially harm your aquarium. Instead, rinse the biological media with water from the tank to preserve the beneficial bacteria while removing debris.

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