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Nitrogen Cycle

Last edited - December 8, 2018

nitrogen cycle diagram

You begin your betta fish keeping adventure by going to your local fish store and buying all the supplies you need for a betta. You spend what seems like an eternity trying to decide what betta food you should get, what decorations would match with each color of betta, and finally which betta to choose. (Dont forget the HEATER!!!). You leave the store excited and quickly go home to prepare the betta's new home. You set everything up, make sure the plants stay put, and then put in the betta. You then sit mesmerized for about an hour or so in front of your aquarium. Everything seems fine, but then in the next few days disaster will strike with the name of New Tank Syndrome.


Is New Tank Syndrome Real?

Although it may seem like a conveniently made up name, New Tank Syndrome is real and is a major cause of death in new tank set-ups not only for bettas, but also for all types of aquariums. New Tank Syndrome occurs when a newly established tank has not completed the nitrogen cycle, which means that it is going to go through a cycle of ammonia, nitrite, and nitrate spikes until all the chemicals become balanced. Putting your betta, or any other fish, through this cycle will stress them out and may possibly kill them.




Nitrogen Cycle: In-depth

Steps of the nitrogen cycle in an established tank

  1. Whenever you feed your betta, ammonium will appear in the form of waste. Ammonium is highly toxic to fish.
  2. The ammonium will then be consumed and converted by Nitrosomas bacteria into nitrites. Relax, they are beneficial bacteria and you wont get sick. Nitrites, although less toxic than ammonium, can still stress your betta out.
  3. Then, the nitrites will be consumed and converted by Nitrospira bacteria into nitrates, which is not very toxic and can only cause harm if there is a high concentration.
  4. In a tank without any live plants, the only way nitrates can be removed is through water changes. However, live plants absorb nitrates and thus are very beneficial in maintaining good water quality for your aquarium. You can read more information about live plants here - Live Plants


In a new tank, however, the nitrogen cycle is not yet established. Because there aren't any beneficial bacteria in a new tank, the chemicals from the fish waste cannot be converted into less harmful chemicals. The tank will go through a few chemical spikes as it tries to achieve a perfect balance. Any fish in the tank at this time will suffer the effects of chemical poisoning. First, ammonium will continue to build up until Nitrosomas bacteria become established. The ammonium levels will then decrease to safe levels. However, because there aren't Nitrospira bacteria yet, the nitrites will also build up until the Nitrospira bacteria colonize the tank. When nitrates appear, the tank has finished cycling and you have nothing more to worry about New Tank Syndrome.

In order to measure the amount of chemicals present in the aquarium, you need to buy a test kit online or from your local fish store that can test for pH, ammonia, nitrites, and nitrates. Although some local fish stores do offer free water tests, it may be more convenient to get a test kit for yourself since you will need to test the water at least every few days to properly monitor the cycling process.



So how do I cycle a tank?

There are two ways - Cycling with fish or without fish, both methods can take 2-4 weeks

  • Fishless cycling (preferred method) - for this you need pure ammonia. Begin by adding as many drops needed to bring ammonium readings to 4-5ppm. When it drops to 1ppm, add more ammonia to bring it back up. When it lowers to 1 in less than a day, test for nitrites. Continue adding ammonia to keep the level stable at 1ppm. When the nitrites reach 0ppm, the tank has finished cycling.
  • Cycling with fish - for this to work you need to purchase a hardy fish such as a zebra danio. Only buy a few, such as 1 or 2, so that the chemical spikes are not drastic. Feed them regularly and measure the amounts of chemical everyday. If you encounter a huge spike, do small water changes until the levels are safe. Once ammonium and nitrite levels read 0ppm and nitrate is present, the tank has finished cycling.


Planted aquarium


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