Aquarium Cycle

How Do Aquarium Filters Work?

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filter PetAquariums How Do Aquarium Filters Work?

You know how air filters clean up the air humans and animals breathe, well that’s also how aquarium filters clean up the water for the benefit of our fish.

So, how do aquarium filters work?

An aquarium filter works buy pumping water through three filter compartments. One compartment filters Chemicals, one compartment is the mechanical part that filters large particles like leftover food. The third compartment is biological, it grows beneficial bacteria which in itself turns ammonia and nitrites into nitrates.

I’ll explain it to you in more detail during the course of this article…

Keep in mind that your filter is one of the most important components of your aquarium. Its functions include catching debris (fish poop included), eliminating toxins, and creating an environment where beneficial bacteria can grow.

Without proper filtration, the tank water will be dirty and contaminated. Such a condition will eventually lead to the death of your fish.

Three Types Of Filtration Systems

There are three main types of aquarium filtration system, they are –

  • Mechanical filtration system
  • Biological filtration system
  • Chemical filtration system

Mechanical Filtration

This is made for the purpose of dealing with bigger aquarium waste, such as fish poop, leftover food, and bits of rotting plants.

The mechanical filtration system has a sponge and filter floss.

To trap the big particles, the floss is first placed in the filter, while the sponge is layered underneath.

Be sure to clean the materials used for mechanical filtration regularly, if you don’t, all the waste particles it picks up will still be in the water and will continue to rot. Also, the filter will become clogged if it is not cleaned regularly.

Cleaning the filter material once in 2 weeks is usually enough to rid it of all the picked up debris.

Clean by squeezing the filter sponge in a bucket of used tank water. Do not use tap water to clean the filter material, this is because you could lose all the beneficial bacteria from the sponge if you do.

Also, do not clean all the sponge at once, do not also replace all the sponge at once (replace half of it first, then the other half a few months later).

You would like to preserve the beneficial bacteria, as they are important to the tank, and cleaning or replacing the whole sponge at once will mean getting rid of most of the bacteria.

As effective as mechanical filtration is, the sponge and floss aren’t the only elements that ensure it does the job, the beneficial bacteria living in the filter also plays a major role too. In fact, without the bacteria colonies, the mechanical filtration system will not be effective.

Biological Filtration

Fish and other aquarium inhabitants produce poisonous ammonia (NH3), which bacteria converts into poisonous nitrite (N02), which other back converts into less poisonous nitrite (N03).

Most of these bacteria live in the aquarium’s filter, but sometimes, they just aren’t enough to tackle all the ammonia being produced in the water.

This is where the biological filtration system comes in.

In the sponge of a biological filter, larger colonies of beneficial bacteria can grow and thrive, which are capable of sustaining a small aquarium ecosystem.

There are different types of biological filters out there, and they all have one thing in common – They need to be left alone without cleaning.

Cleaning would only disturb your biological filter media, which can lead to ammonia spikes, and this is not good for the fish.

Chemical Filtration

This is the least popular type of aquarium filtration, and it is done with activated charcoal.

Activated charcoal used to be a vital part of aquarium filtration systems because it removes invisible pollutants. A process called “adsorption”.

In recent years, the use of activated charcoal has significantly declined. This is because it not only removes invisible pollutants, it also removes many vital trace nutrients that the fish need.

There are other types of chemical filtration systems, such as peat moss (used for lowering pH levels), zeolite (used for eliminating excess ammonia).

Even with filters, your tank will still need regular cleaning. Before you buy a filter for your tank, be sure to first consider the right combination of biological and mechanical media you will need.

Why You Need Bacteria To Grow In Your Filters

Many aquarium owners have wondered why it’s important for bacteria to grow in their filters. Well here’s the answer –

Beneficial bacteria is known for feeding on the waste produced by fish and converting them into less toxic substances. This helps keep the tank water clean and less poisonous to your fish.

This process is what is popularly known as the Nitrogen Cycle.

Here’s a brief breakdown of this cycle –

  • Your fishes eat food
  • Your fishes will poop (manufacture waste)
  • The waste will decompose and create ammonia
  • The beneficial bacteria will consume the ammonia and convert them to nitrates

P.S – Beneficial bacteria is also known as nitrifying bacteria.

Are Nitrates Harmful

Yes, they are, but only when in large concentrations. Other than that, nitrates are important to aquarium plants for the process of photosynthesis.

You can get rid of nitrates by simply changing the water.

Where Does The Beneficial Bacteria Grow?

Beneficial bacteria (nitrifying bacteria) grows everywhere in your aquarium. However, the biological media in your filter is where you will find the most growth.

The filter constantly supplies well-oxygenated water, while its biological media provides enough space for the beneficial bacteria to grow.

The function of the sponge itself is to keep the water clean of any floating debris, while the carbon is there to remove coloration smells. The carbon can also help remove some toxins which the beneficial bacteria might have missed.

How To Get Beneficial Bacteria To Grow In Aquarium Filters

Well, the process is pretty simple and straight forward. The bacteria will naturally latch on to fish waste and other organic materials in the water (like leftover food).

The filter cleans the organic waste up so it is stuck in the sponge, meaning the bacteria will mostly be found there.


I trust this article has answered your question – how do aquarium filters work? I also hope the extra information provided here will be of great help.

Take care!

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Pet Aquariums

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