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The Nitrogen Cycle

Tropical Fish Keeping – Aquarium Water Filtration

Proper water filtration is essential to successful tropical fish keeping.

Your aquarium’s water filtration system is responsible for eliminating toxic compounds and particulate matter from your fish tank.

Fish give off waste products in the form of feces, uneaten food, carbon dioxide, etc. and the water in the tank begins to degrade immediately after the introduction of the first fish, plant, live rock, or invert.

Pollution begins in your aquarium the moment you introduce the first fish into your tank.

Without proper filtration in a closed aquarium system, the tank water will degrade to the point that it will become toxic and eventually poison the inhabitants.

Three types of filtration is necessary to maintain the health of any freshwater or saltwater aquarium fish.

  • Mechanical Filtration
  • Biological Filtration
  • Chemical Filtration

It is extremely important that you select the correct type of filtration system for your aquarium.

Your selection will be dependent on several things:

  • The type of fish you are keeping
  • The amount of fish you are keeping in the tank
  • The water volume of your tank
  • The surface area of your tank
  • The amount of time you want to devote to maintenance

It is important that you understand how the three types of water filtration systems will effect your personal situation before you make your purchase.

Although there is no such thing as “over filtration”, some of the systems or combinations of systems could bust your budget.

Mechanical Filtration

Mechanical filtration is the process of removing solid particulates from aquarium water.

It is normally accomplished by forcing water through some type of media that is specifically designed to trap and hold the particles.

Many types of filter media is available to do this effeciently and each has its pros and cons.

  • Filter floss
  • Foam in different porosities
  • Pleated paper micron filters
  • Diatomaceous earth
  • Gravel
  • Sand

Whatever media is used to remove solid particulates from the water must be cleaned on a regular basis in order to work properly and maintain its efficiency.

Eventually, all mechanical filters will clog up with particulate matter over time. When this happens, the water flow will decrease and eventually cease. The dirty tank water will then flow around the clogged media instead of going through it. When this happens it signals that a cleaning is necessary.

Some tropical fish keepers believe that oversizing the mechanical filter will allow you to keep more fish in the system and that less maintenance will be necessary. This is a fallicy.

Although you may not feel the need to clean the mechanical filter as frequently when you oversize it to your tank, the filter loses its efficiency and will be holding a greater amount of decaying detritus that is slowly contaminating the water.

Although your tank may look clean and free of floating particles, the slowly decaying plant and animal matter in the media is breaking down and creating ammonia, nitrites and nitrates which are all toxic to the fish.

The point is that oversizing a mechanical filter to your tank can actually reduce the number of fish you can safely keep in the aquarium.

Biological Filtration

Biological filtration is simply the bacterial breakdown of toxic byproducts in the aquarium into less toxic nutrients. The bacterial breakdown process is commonly called the Nitrogen Cycle.

The Nitrogen Cycle can be explained as follows:

Waste products from fish, plants, and invertebrates and dead organisms or uneaten food, are broken down by bacteria and fungi into ammonia.

Ammonia is extremely toxic to all aquarium fish, but in the biological filter it is broken down by oxygen loving Nitrosomonas bacteria into less toxic nitrites.

Although the nitrites are not as toxic as ammonia, they are still harmful to fish and especially invertebrates in even low concentrations.

Fortunately, another oxygen loving bacteria called Nitrobacter acts like Nitrosomonas in the biological filter and changes the nitrites into harmless nitrates, which are less harmful to fish.

Low to moderate levels of Nitrates will not harm fish or most inverts but they can cause some serious algae problems in your tank. You can reduce this by performing reglar partial water changes or by including chemical filtration to your system.

To some extent, biological filtration occurs in all filters as well as inside your tank. However, for the Nitrogen Cycle to work efficiently two things are required.

A large area for the beneficial bacteria to live and grow on.
Sufficient oxygen in the water to keep the bacteria colony alive.

Obviously not all filters have the same biological filtration capacity. The most efficient biological filtration systems are those that have the greatest amount of biological surface media exposed to the air.

Chemical Filtration

As the name implies, Chemical filtration removes toxic and unwanted chemicals from the tank water as it passes through some sort of chemical media.

Activated charcoal or carbon has been used for years to provide chemical filtration however, there have been a number of new products over the years that are targeted at removing specific chemicals or excess nutrients from the water.   The most popular types of chemical media are activated carbon, ion exchange resins and other adsorbents.   Other forms of chemical filtration are protein foam skimming and ozone oxidation.

Activated carbon will remove many harmful elements from your aquarium including sulfa drugs, antibiotics, dissolved proteins, chlorine, copper, carbohydrates, etc.

For this reason it should be removed when treating your aquarium with antibiotics or other medications and replaced after the treatment is complete to remove any leftover medication or discolorants.

Ion exchange resins are used less frequently than carbon but are becoming more common.

Resins work by attracting specific mocules to them.  Some attract mitrates or ammonia and some target dissolved organics.  Some ion exchange resins strengthen the ability of carbon to chemically filter dissolved particles from the water and help biological activity by removing pollutants before they enter the nitrogen cycle.  These are sold as carbon/ion mixes under several brand names.

When used correctly, Chemical filtration can be one of the most useful tools that tropical fish keeping enthusiasts have for  improving water quality, reducing the amount of water changes needed  and the amount of tank maintenance that has to be performed in order to maintain a healthy aquarium.

This does not mean you will never have to make another water change!


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