How Does a Fish Tank Filter Work?

Estimated read time 3 min read

Your filter is one of the most important parts of your aquarium as it helps catch debris, clears toxins from the water and provides a great place for the beneficial bacteria to grow and prosper.


A Few Of My Favorite Fish Tank Filters That Work Really Well

But How Does A Fish Tank Filter Work?

The short answer: The filters primary purpose is to create the ideal space and conditions for nitrifying bacteria to grow. This nitrifying bacteria helps remove harmful toxins from your water that are a result of decaying organic matter and fish waste. Your filters mechanical media then helps remove any excess food & free-floating particulates from your aquarium keeping the water clean.

Watch this video and learn how a fish tank filter works

Why do we Need Bacteria to Grow in Our Filters?

Beneficial bacteria feed on the waste from your fish and transform it into less toxic substances which helps keep your aquarium water clean and healthy for your fish.

This process is called the nitrogen cycle, and it’s pretty simple:

  1. First, your fish eat food
  2. Then they create waste (poop)
  3. The fish waste decomposes creating ammonia.
  4. Then the beneficial bacteria (nitrifying bacteria) eat up the ammonia and eventually create nitrates.

Please note: Ammonia is super toxic to fish and if you allow it to build up it can burn your fish’s gills and eventually lead to fish death.

Are Nitrates Bad?

Nitrates are bad, but in small concentrations, they are pretty harmless and you can get rid of nitrates easily by doing a water change or by keeping live plants which will use the nitrates as part of the photosynthesis process.

Where Does The Beneficial Bacteria Grow? 

It grows almost everywhere inside your tank. But the biological media inside your filter is where a good majority of it will grow.

The bio media is designed to provide a large surface area for bacteria to grow, while your filter provides a constant supply of well-oxygenated water.

The sponge in your filter is used to keep the water physically clean floating debris so that the water is visually clean

Additionally, the carbon in your filter helps remove coloration, smells and other toxins that may be present at the bacteria simply won’t touch effectively creating a trifecta of aquarium

How do I Get Beneficial Bacteria to Grow in my Filter? 

Very easily, you can use additive products specifically designed to help keep your aquarium bacteria levels up

For New tanks you can use: Seachem Stability to help kick start the nitrifying bacteria growth.

For an established tank: you can use a booster like Seachem Pristine.  

Try to use these products after a filter cleaning or water change to ensure you don’t lose too much bacteria during a cleaning.

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