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The Nitrogen Cycle

Nitrogen Cycle

Nitrogen Cycle

The most common mistake that many beginning tropical fish keeping enthusiasts make is to stock a new tank with as many fish as possible without first establishing a healthy, stable, ecosystem in the aquarium. This is done through a natural process called the Nitrogen cycle.

Nitrogen Cycle:

All fish release toxic wastes that in an enclosed environment will eventually contaminate the water in the aquarium. Uneaten food and fish waste in an enclosed system will break down and release toxic ammonia into the tank water.  In a river, lake, or stream, the amount of ammonia created by the fish is negligible but in an aquarium, it can quickly become lethal.

The Nitrogen cycle is a natural two step process that establishes colonies of beneficial nitrifying bacteria (Nitrosomonas) in the aquarium that metabolize toxic compounds and renders them harmless to fish.

The beneficial nitrifying bacteria once established in the aquarium will convert toxic ammonia into Nitrites, which are less harmful to fish.    Although Nitrites are not as harmful to the fish as ammonia, they are still toxic.

After a sufficient number of Nitrites appear in the tank, a different type of bacteria , (Nitrobacter)  will begin to develop that will convert the Nitrites into Nitrates which are generally safe for most species of fish.

Excessive Nitrate buildups can also cause problems in an aquarium but are easily controlled with regular tank water changes.   Floating and submerged plants use Nitrates as fertilizer and are used to control buildups.

The entire Nitrogen cycle process can usually be accomplished within a month, but can take as long as two months to complete.

An aquarium is considered completely cycled when it contains zero traces of ammonia or Nitrites; and a minimal amount of Nitrates.

Speeding Up The Nitrogen Cycle:

Because most tropical fish keeping enthusiasts are impatient and want a beautiful tankful of fish as soon as possible, they naturally want to know if the Nitrogen cycle process can be accelerated. The answer is YES. There are several ways to safely speed up the Nitrogen Cycle process.

The safest way to accelerate the growth of beneficial bacteria and speed up the Nitrogen cycle process in a new aquarium setup is to add water, gravel, and aged filter media from an aged, already established aquarium.

Transferring some gravel and/or up to 100% of water from an established aquarium will significantly reduce the amount of time it takes to cycle a new system.

Adding “seeded” filter media from an established tank will dramatically decrease the amount of time it takes to complete the Nitrogen cycle process from several weeks to only a few days.

When using the “seeding” method, it is important that only HEALTHY established tanks are used for the transfer of beneficial bacteria. There is always the possibility of introducing unwanted microorganisms, parasites, and even disease into a new system when water from a “sick” or previously treated tank is used.

Aquarium starters of live beneficial bacteria are sold in most pet shops as a way to “jump start” and reduce the time it takes to complete the Nitrogen cycle process. Live bacteria help boost the biological filter in new systems, destroy sludge buildup in the gravel bed, and help to keep plants and aquarium glass clean.

The effectiveness of using this method depends entirely on the freshness, quality, and amount of live bacteria in the bottle. Some tropical fish keeping enthusiasts swear by this method, while others prefer the natural cycling method.

API StressZyme, API Quick Start, Fluval Biological Enhancer, and Aqueon Pure Bacteria supplement are a few products that are available.

We have found from many years of experience that allowing the nitrogen cycle to take place naturally results in a more stable aquarium. Using beneficial bacteria to “quick start” the Nitrogen cycle is effective but can lead to an overly imbalanced aquarium.

Fishless cycling:

Instead of introducing live fish into a new aquarium setup and waiting for them to create ammonia in the tank; some tropical fish keeping enthusiasts choose to cycle their new systems using ammonia chloride or ammonium hydroxide.   The idea is to mitigate stress and the potential loss of fish during the cycling process.

Although this method results in a very stable colony of beneficial bacteria, it requires a lot of patience and water testing.

To cycle a new tank without using fish, you will need a source for ammonia, a water testing kit, de-chlorinator, a heater, and a filter that you will be using in the new tank.

First fill the tank with de-chlorinated water and set the water temperature to about 85 degrees F.

Next, slowly add ammonia chloride or ammonium hydroxide a few drops at a time until the the ammonia level test reaches 3ppm to 4ppm. Add only 2 or 3 drops at a time over periods of a half hour or so to allow adequate dilution. Do NOT use ammonia products for home use that may have other chemical additives. The other chemicals are often deadly to fish.

Make daily water tests until the ammonia levels in the tank drop down to around 0.5ppm – 1ppm; then add more ammonia to bring levels back up to 3ppm to 4ppm. Continue doing this daily until the nitrite levels start going up. This should take only a few days.

Continue daily testing for ammonia and nitrites.   After a few weeks the nitrite levels will begin to drop. When the ammonia and nitrite levels both show 0 ppm, the nitrate levels should be going through the roof. When the Nitrate test readings get up to 30 ppm, make a 70 to 80% water change to bring them down. At this point, the beneficial bacteria should already “seeded” into the aquarium filter, aquarium gravel, and decor.

Next, add a final dose of ammonia to bring the test level up to around 4 ppm and wait 24 hours before making another test. The readings should then test 0 for both ammonia and nitrites.

At this point the tank is fully cycled and fish can be slowly added to the system. Be sure to continue testing after new fish are introduced to ensure that no sudden spikes occur.

Cycling with fish:

Most tropical fish keeping enthusiasts use hardy fish like Zebra Danios to cycle their aquariums. This method requires constant water changes and daily testing of ammonia, nitrite, nitrate and pH levels.

First fill the tank with de-chlorinated water and make sure to use both a mechanical and biological filter.    These hold the largest amount of beneficial bacteria.

Start the Nitrification process by adding one or two hardy fish per 10 gallons of water into the aquarium until the Nitrogen cycle is completed. The fish waste, uneaten food, and nu-noticed dead corpses will create the ammonia necessary to begin the Nitrogen cycle.   Additional fish can be gradually added when the tank is fully cycled.

Test the water daily for ammonia. Ideally, the ammonia levels should be maintained under .25 ppm. If you see that the ammonia levels go past .5 ppm, perform a 50% water change with de-chlorinated water.   Chlorinated tap water will kill the beneficial bacteria you are trying to cultivate in the tank.

When the ammonia level in the aquarium go down, start testing for nitrites and conduct water changes when necessary to keep the levels under .25 ppm.

When the ammonia and nitrite readings reach 0, the nitrogen cycle has completed and new fish can be gradually added to the aquarium. Don’t add too many fish at one time or ammonia levels will begin to spike.

After adding any new fish, it’s a good idea to test the water for a few weeks to ensure that there are no sudden ammonia spikes.

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