Aquarium Biofiltration



Biofiltration is simply maintaining the nitrogen cycle in an aquarium.  What then is the Nitrogen Cycle?

As with all living creatures, fish give off waste products (pee and poo). These waste products break down into ammonia (NH3), which is highly toxic to most fishes. In nature, the volume of water per fish is extremely high, and waste products become diluted to low concentrations. In aquariums, however, and more so in a mini aquarium, it can take as little as a few hours for ammonia concentrations to reach toxic levels.

How much ammonia is too much? The quick answer is, if a test kit is able to measure it, you’ve got too much meaning it’s in a high enough concentrations to stress fish.  A sequence of partial water changes to dilute ammonia to safer concentrations should immediately be carried out.

Simply put, the nitrogen cycle is the biological process that converts ammonia into other, relatively harmless nitrogen compounds. Fortunately, several species of bacteria do this conversion for us. Some species convert ammonia (NH3) to nitrite (N02-), while others convert nitrite to nitrate (NO3-). Thus, cycling the tank refers to the process of establishing bacterial colonies in the filter bed that convert ammonia to nitrite and then to nitrate.

The desired species of nitrifying bacteria are present everywhere e.g., in the air. Therefore, once you have an ammonia source in your tank, it’s only a matter of time before the desired bacteria establish a colony in your filter bed.

The most common way to do this is to place one or two hardy and inexpensive fish in your aquarium.  Any more may lead to their death before the filter can catch up.  The fish waste contains the ammonia on which the bacteria live. Do not overfeed them! Common goldfish often do nicely.

During the cycling process, ammonia levels will go up and then suddenly drop as the nitrite-forming bacteria take hold. Because nitrate-forming bacteria don’t even begin to appear until nitrite is present in significant quantities, nitrite levels shoots up as the built-up ammonia is converted, continuing to rise as the continually-produced ammonia is converted to nitrite. Once the nitrate-forming bacteria take hold, nitrite levels fall, nitrate levels rise, and the tank is fully cycled and in equilibrium.  Ammonia and nitrite levels should then be zero.

A simple test kit would be able to determine when the cycle has completed. This cycling process normally takes about 2-4 weeks.

One common mistake is adding too many fish before the tank has fully cycled increasing ammonia production, stress on all fish and the likelihood of fish deaths. This is often known as the New Tank Syndrome.

In an established tank, ammonia should be undetectable using standard test kits. The presence of detectable levels indicates that your bio filter is either not working adequately e.g., too small for fish load or your tank has not yet cycled.

Although you can use products like Ammo-Lock to treat ammonia, such products do not remove the ammonia, it simply neutralizes it.  Biological filtration is still needed to convert the neutralized ammonia to nitrite and nitrate.

The nitrogen cycle can also be speeded up in a number of ways. One is by way of taking some of the bacteria out of an established tank, then placing them in the new tank.  Most filters have some sort of foam block or glass wool insert on which nitrifying bacteria attach. Taking some or all of such an insert and placing it in the new tank’s filter gets things going more quickly.  If the established tank has gravel, there will be nitrifying bacteria on it too.

Although you can also get products with colonies of nitrifying bacteria at pet shops do note that bacteria, hardy as they may be cannot live indefinitely without oxygen and food. Thus, even freshness is no guarantee as they can be adversely effected by poor handling and storage conditions.

You can also get filter material or gravel from an established tank from your pet shop although you must be careful as these are also likely to contain unwanted pathogens and parasites as they regularly top up their supply of fish which may come from different sources.

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