Biological Filtration

The biological filtration process is difficult to understand for some. Good bacteria called nitrifying bacteria converts ammonia into nitrates and then the nitrites are converted into nitrates. This good bacteria is found naturally in our environment.

Good beneficial bacteria needs three things to grow in your home aquarium.

  • A place to grow
  • Food
  • Oxygen

A Place to Grow

The home that the beneficial bacteria will thrive in your aquarium tank can be in the tank itself or in your filter. The bacteria will grow in your aquarium gravel, plants, and decorations. The place where most will grow and multiply will be in your aquarium filter media.

galaxy rasboro, celestichthys margaritatusSurface area is very important when selecting biological filter media. The larger the surface area of the media, the more beneficial bacteria will be found in your filter. Porous ceramic media or sponges house a large amount of beneficial bacteria. The biological media must have sufficient water movement through it so the media does not clog with waste therefore negating the process of biological filtration.


The beneficial bacteria will eat the fish waste (poop) and left over food in your fish tank. The result is ammonia.

Ammonia can be deadly to your tropical fish. Luckily, your beneficial bacteria feed on ammonia! The ammonia is then converted to Nitrite. Nitrite is yet another potentially deadly pollutant.

Guess what!

The bacteria will now feed on the nitrite and convert this to a less harmful product called nitrate. Nitrate can still be harmful if left in the tank and in large quantity. Nitrate levels can be reduced through regular water changes.


The last requirement that your beneficial bacteria will need to survive is oxygen. The bacteria in your biological filter are aerobic. Aerobic means that oxygen is needed for survival.

Some filters provide for more oxygen in the water and filter than others. We-dry filters do add more oxygen by allowing water to slowly poor over the filter media keeping the media wet enough for bacteria to thrive. 

In order to properly grow your beneficial bacteria colony, be sure to select the best Biological Filter Media available for a healthy tropical fish tank. 

Fish Tips

When cleaning your filters, be sure to wash your filter media out with aquarium water in a bucket. Do not run it under the sink unless you have more than one filter on your tank.

If you have more than one filter on your tank, you can clean your filter media under the sink faucet but you need to wait a few weeks to clean the other filter. This will allow the bacteria to build up enough in the clean filter media before you wash your other filter’s media. You do not want to deplete your beneficial bacteria totally because your water could go through a mini cycle.

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