Aquarium Nitrogen Cycle

Aquarium Nitrogen Cycle is perhaps the most important knowledge in fish keeping hobby. It is essential for the survival of fish in an aquarium. Without continuous nitrogen cycle in an aquarium, most fish will drop like flies within weeks.

What is an Aquarium Nitrogen Cycle?
The nitrogen cycle for an aquarium is the natural occurring process of the toxic ammonia (NH3) being converted to nitrite (NO2), then the nitrite is converted to the relatively harmless nitrate (NO3).

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

What is ammonia?
Ammonia is a form of nitrogen compound. It is toxic. It will cause burn to the fish’s gills in even the slightest amount, and the continuous exposure to just a tiny trace of ammonia will eventually kill the fish. Moreover, ammonia poisoning is one of the leading causes for fish dying in home aquariums. This is especially true in 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 included. Not only the fish produce ammonia directly through their gills on a constant basis, their poop also creates more ammonia when it breaks down. All the other organic matters in the aquarium such as leftover fish food, decay plants, and in some cases dead fish, will also contribute to the increasing level of ammonia in the water. While this is not a problem at all in a natural environment with nearly unlimited amount of water (ex: rivers, lakes, oceans), ammonia is not going anywhere in a closed system such as in a home aquarium.

How do I get rid of ammonia?
While certainly you can remove ammonia manually from an aquarium by doing water changes, this does not remove all of it and it is not the permanent solution since ammonia is produced on a constant basis in an aquarium as long as there is fish in it. Even if you do 100% water change every day (not recommended because it will shock the fish), 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.

In a well established home aquarium or a “cycled tank”, there will be 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 end result is the harmless nitrate. Both species of beneficial bacteria will continue to grow in number in an aquarium, until 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 should always have 0ppm readings on both ammonia and nitrite.

While both species of beneficial bacteria exist naturally in the water, the number in any newly set up aquarium is always near zero, and 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 into a new fish tank, the ammonia level will start to rise and it will never be 0ppm until the tank is cycled. However, the fish will usually die to ammonia poisoning before the aquarium cycle can be completed, because it usually takes many weeks or even months before there are enough good bacteria to do the job. The solution is simple. You need to have sufficient amount of nitrosomonas and nitrobacter bacteria in a new fish tank before you can safely add fish without them dying within weeks.

The Aquarium 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 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 a number of days, and they believe that will make the fish tank ready for fish. Having an empty tank full of water will achieve nothing even if you let it sit for many years. Since the good 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/or raw fish
3. Cycle with fish (Fish-in Cycle)

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