Aquarium Nitrogen Cycle In Fish Tanks

Aquarium Nitrogen Cycle is perhaps the most crucial knowledge in fish keeping hobby. It is essential for the survival of fish in a captivity environment. Without continuous nitrogen cycle, most fish will drop like flies within weeks.  Learning aquarium nitrogen cycle is the very first step to keep aquarium fish like a professional.

What is an Aquarium Nitrogen Cycle?

The nitrogen cycle in an aquarium is the naturally occurring process of converting the toxic ammonia (NH3) to nitrite (NO2).  Then it turns the even more toxic nitrite to relatively harmless nitrate (NO3).

Ammonia (NH3) —>>> Nitrite (NO2) —>>> Nitrate (NO3)

What is ammonia?

Ammonia is a form of the nitrogen compound. It is toxic. It will cause burn to the fish’s gills in even the slightest amount.  The continuous exposure to just a tiny trace of ammonia will eventually kill the fish. Moreover, ammonia poisoning is one of the leading causes of fish dying in home aquariums.  It is especially true for newly set up aquariums. In a healthy aquarium, the ammonia concentration should be absolutely 0ppm (part per million).

Where is the ammonia from?

Almost all live organisms on the planet earth give off ammonia as a waste. Fish is no exception. The fish produce ammonia directly through the gills on a constant basis.  Their poop also produces more ammonia when it breaks down. All the other organic matters in the aquarium such as uneaten fish food, decay plants, and in some cases dead fish, also contribute to more ammonia in the water.  It is not a problem at all in a natural environment with a nearly unlimited amount of water.  (e.g., rivers, lakes, oceans).  Ammonia is not going anywhere in a closed system such as in a home aquarium.

How to remove ammonia?

Water Change alone never removes all ammonia

You can certainly try to remove ammonia manually from an aquarium by doing water changes.  This method does not remove all of it.  It is not a permanent solution.  Ammonia is produced on a constant basis in an aquarium as long as there is fish in it. Even if you do a 100% water change (not recommended) every day, ammonia will always build up between two water changes. You will never be able to keep it at 0ppm with water changes alone. This is where aquarium nitrogen cycle comes in.

A cycled aquarium takes care of ammonia and nitrite on a constant basis

We call a well-established home aquarium a “cycled tank.”  There is a species of waterborne bacteria called Nitrosomonas feed on ammonia as a food source. They convert ammonia to nitrite as a result. Nitrite is just as if not more toxic than ammonia. A second species of waterborne bacteria called Nitrobacter will come in and feed on nitrite as food. The result is the harmless nitrate. Both species of beneficial bacteria will continue to grow in number in an aquarium.  Until the point, they reach a balanced level where their combined appetite cancels out the production of ammonia and nitrite. As a result, all the well-established aquariums always have 0ppm readings on both ammonia and nitrite, with an increasing nitrate.

It is a good idea to cycle a fish tank before getting any fish

Both species of beneficial bacteria exist naturally in the water.  However, the number of them in any newly set up aquarium is always low.  It is nowhere near sufficient enough to keep ammonia and nitrite both at zero ppm which is required to keep your fish alive. The moment you add fish to a new fish tank, the ammonia level will start to rise.  It will never be 0ppm until you have cycled the tank. Furthermore, the fish will usually die from ammonia poisoning before the aquarium cycle is complete.  Because it often takes many weeks or even months before there are enough good bacteria. The solution is simple. You need to have sufficient amount of Nitrosomonas and Nitrobacter bacteria in a new fish tank before adding fish.

The Aquarium Nitrogen Cycling

The process of “growing” efficient amount of Nitrosomonas and Nitrobacter in a newly set up fish tank is called cycling an aquarium.  Or fish tank cycling. It is the safest way to make sure your new aquarium is ready.  So it can handle the amount of ammonia produced by the fish before you even add the fish.

A lot of fish beginners took the wrong advice of letting the fish tank sit for some days. They believe all this sitting will prepare the fish tank for fish. Having an empty fish tank full of water will achieve nothing even if you let it sit for many years. Since the beneficial bacteria need a source of ammonia to begin their growth, the aquarium nitrogen cycle won’t even start until you add a source of ammonia.

The three most common methods to cycle fish tanks

1. Fishless Cycle with pure ammonia

2. Fishless Cycling with fish food, or raw shrimp and raw fish

3. Cycle with fish (Fish-in Cycle)

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