Understanding The Nitrogen Cycle

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Understanding the nitrogen cycle and its importance to a healthy tank is imperative for the serious fish-keeping hobbyist. The nitrogen cycle in your tank occurs constantly - it reflects how efficiently waste is broken down in your fish tank. In this article, we discuss how the nitrogen cycle helps clear tank water of metabolic wastes and why the maturation period matters with new tanks. We will also cover how to kick-start a new tank's cycle, how to check your tank's nitrogen cycle and how to improve your tank's nitrogen cycling in general.


How the Nitrogen Cycle Helps Recycle Metabolic Wastes

In nature, when animals expel their wastes and plants decay, anaerobic bacteria in the environment break down waste to harmless nitrogen that is released into the air through the ground and water. If nature did not have some mechanism for using the "waste" material, eventually, we would run out of good stuff. Luckily, through the participation of bacteria using these waste substances, harmful materials (to animals) like ammonia are converted into something harmless and useable again. Two kinds of bacteria participate in this cycle: Nitrite Bacteria (Nitrosomonas) and Nitrate Bacteria (Nitrobacteria). This process of breaking down animal wastes is called Nitrification.

In Nitrification, we have:

Animal waste (ammonia) is converted by Nitrosomonas → Nitrites is converted by Nitrobacteria to → Nitrates

What Happens When You Keep Fish In Tanks?

Out of fish waste, the chemical we worry about most in a tank is ammonia since it is most toxic of the metabolic byproducts to fish. In the tank, without proper filtration, the ammonia level accumulates in the water, building up to toxic levels eventually killing the fish. Besides the ammonia level, the actual level of debris would also reach a critical mass rendering the water unlivable for inhabitants. Fish live in water and not mud!

The process of clearing aquarium water of ammonia, nitrite and nitrate is a major goal of biological filtration; the other two main aims of tank filtration being mechanical filtration and chemical filtration. Setting up tank equipment to facilitate biological filtration (i.e. nitrification) is paramount to establishing a healthy tank.

Why the Maturation Period Matters to the Nitrogen Cycle

The funny thing about the nitrogen cycle is you have a bit of "What came first, the chicken or the egg" going on. To get the nitrogen cycle established, you must have enough ammonia in the tank to get bacteria levels up high enough to take care of the fish' waste. If bacteria levels are not high enough to meet the output levels of fish introduced in the tank, fish will have a hard time surviving in the water until bacterial levels catches up. Establishing the balance challenges every owner of a new tank, even experienced fish-keepers. When new hobbyists jump the gun and put their fish in before their bacteria levels are high enough, they will unfortunately experience "New Tank Syndrome." New Tank Syndrome is when fish, recently introduced to a new tank, die off due to high levels of ammonia, nitrates and nitrites in the water before sufficient bacteria levels were established. Before you can safely introduce fish to a new tank, the tank must be "Cycled".

To cycle a tank, you need to add a form of ammonia and a "starter" colony of bacteria to the water. The old school way to cycle a tank would be to introduce the hardiest fish you could find. This method is bad because you end up sacrificing the "starter" fish since the biological filter will not get established fast enough to clear the water of ammonia levels for those fish. When nitrite levels remain at zero for a week, the tank is considered matured and ready for live inhabitants. Normally, the nitrogen cycle takes two to six weeks to establish in a new tank. Rarely do new fish hobbyists wait two to six weeks to fill their tanks!

How To Kick-Start Your Nitrogen Cycle In a New Tank

In general, you can cycle a new tank without sacrificing starter fish. You need an ammonia source and a bacteria source. This webpage has a good article on fishless cycling: http://www.aquariumsecrets.com/Fishless.htm in general. To "seed" your tank, you could try any of the following ways:

  • 1) If you can get established tank water you know is free of parasites, etc., to start cycling the tank.

     
  • 2) Introduce live rock to your tank first before your fish; live rock should produce enough waste material to get the bacteria going. If you want more information on using live rock, check out this page: http://wetwebmedia.com/estbiofiltmar.htm

     
  • 3) Another method of cycling a tank is by putting in fish food without fish! Fish food will eventually decay resulting in the much desired ammonia. This page discusses going this route: http://www.wetwebmedia.com/lrstudiesfj.htm

     
  • 4) You can also seed the tank with pure ammonia. Add ammonia directly to the tank and let the bacteria bloom in respond. These websites discuss going this route:


Products on the market can help you mature your tank but they are not necessary. These products include:


How to Check Your Tank's Nitrogen Cycle

When monitoring your tank water, any ammonia in the water is too much. Because you get the ammonia level down does not mean you are out of the woods. Too much nitrite and nitrate in the water is not good for fish, either. To check the tank's water quality as regards to ammonia, nitrite, and nitrate levels, you will need to use a test kit.


Test kit choices include powder tests, liquid tests, and strip tests. All of these tests are "colorimetric" meaning you compare how the sample water compares to a color chart. You can buy electronic monitors for pH and oxygen level but you are stuck testing ammonia, nitrite, and nitrate levels the old fashioned way. When buying these tests, consider you should test your tank water at least once a week (most experts advocate every other day or daily).

- Dry Regent/Powder Tests

With dry regent or powder tests, you take your tank water, pour it into little test tubes, add test powders for each test type, mix powder into the sample water, and then compare the test tube water with a color chart to see what the level is for each chemical monitored.

  • Pros. Cheap.
  • Cons. Powder is messier than liquid tests or strip tests. You'll need to keep track of your test tubes. Watch the expiration dates for the powder; using reagents after their expiration day may result in inaccurate test results.
  • Cost. Aquarium Pharmaceuticals puts out a FasTestT Ammonia, Nitrite, Nitrate, and pH test kits. Cost is $9.49 for the Ammonia kit, $7.49 for Nitrite from Drs. Foster and Smith; each kit includes 20 tests and you can buy refills at a reduced price after you get the initial set up.

- Liquid Tests

  • Pros. Easier to pour than powder tests and faster dissolving. Cheaper than strip tests.
  • Cons. More to mess with than strip tests. More expensive than powder tests.
  • Cost. Red Sea Mini Lab makes liquid tests for ammonia ($12.25 for 45 tests), nitrite ($10 for 80 tests), and nitrate ($12.25 for 60 tests); these are available from MarineandReef.com.

- Strip Tests

  • Pros. Strip tests are easy to administer. You dip the strip into the water and you'll get your results in seconds. You do not have to worry about chemical mixing or keeping your test tubes.
  • Cons. More expensive than other tests.
  • Cost. A pack of 25 strips will set you back $13.99 (Drs. Foster and Smith package of both 5-in1 test kit and ammonia dip test strips). MarineandReef.com sells the Lifegard 6 Way Test Strip (25 for $19.80) includes tests for ammonia, nitrite, and nitrate.

How to Improve Your Tank's Nitrogen Cycle

We want to focus on biological filtration equipment as well as limiting waste ending up in the tank in the first place. Ammonia levels come straight from fish waste, uneaten food, and rotted plant material. To cut down ammonia, concentrate your efforts on reducing the sheer bulk of waste in your tank (feed fish less, keep dead or dying plants out of the water, and improve the mechanical filtration systems). To help the nitrogen cycle in the tank, consider having as many biological filters as you can work into your aquarium's design. For saltwater tanks, protein skimming is a must. Help things out with frequent water changes.

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