The Nitrate Cycle

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The Nitrogen Cycle

by Rob Strohschein, ReefCavern.com

The Nitrogen Cycle

One of the first lessons a new aquarium hobbyist encounters (after the mechanics of setting up the new fish tank) is the lesson of patients while waiting for the tank to “Cycle”. The Nitrogen cycle can take anywhere from two to ten weeks to complete. It entails introduction of organic material into the system, release of ammonia from the organic material breaking down, Ammonias being converted to Nitrites, Nitrites being converted to Nitrates, and finally Nitrates being removed from the system.

It is imperative that the reef keeping enthusiast understand this process, otherwise they will be met with great frustration and most likely costly expensed due to frequent livestock deaths as fish and invertebrates do not tolerate ammonias, nitrites, or nitrates well. Additionally, water clarity and algae infestation also accompanies poor water quality.

Once you have a basic understanding of the Nitrogen Cycle, tracking and management of it will become much easier. But, because there are so many variables associated with the cycle process testing is required to keep your reef system within safe operating parameters. There are many things you can monitor and regulate within the reef but the three you need to watch within the Nitrogen Cycle are Ammonia, Nitrites and Nitrates. Test kits are widely available and come in various forms. Aquarium Pharmaceutical’s kits are economical and accurate. Each test type can be either purchased separately (Ammonia Test, Nitrite Test, Nitrate Test) or in a bundled kit containing the most common tests.

Below is a short discussion of the Nitrogen Cycle and the value of frequent testing and water changes. Notice in the diagram that the Nitrogen Cycle is not truly a cycle without some intervention. This is the critical factor within the process. The testing mentioned above is used to monitor and manage each step of process.

Nitrogen Cycle

During the initial cycle, test your aquarium water every other day and write down your readings. You will first see ammonia levels rising. Next the nitrite levels will rise as ammonia levels fall off. Finally, the Nitrites will begin to drop and Nitrates will begin to rise. When you no longer detect ammonia or nitrites but you can detect nitrates you can assume that it is safe to add your tropical fish, but go slow.

Nitrogen Cycle Stages
Stage 1
Ammoniais introduced into the aquarium via tropical fish waste and uneaten food. The tropical fish waste and excess food will break down into either ionized ammonium (NH4) or un-ionized ammonia (NH3). Ammonium is not harmful to tropical fish but ammonia is. Whether the material turns into ammonium or ammonia depends on the ph level of the water. If the ph is under 7, you will have ammonium. If the ph is 7 or higher you will have ammonia. Saltwater systems operate safely at a PH of between 7.8 and 8.4.

Stage 2
Soon, bacteria called nitrosomonas will develop and they will oxidize (eat) the ammonia in the tank. The byproduct of ammonia oxidation is Nitrites. Now that the toxic Ammonia is gone we have Nitrites to deal with as they are also very toxic. Using a test kit will show a rise in Nitrites after about 2 weeks into the cycle.

Stage 3
As the tank matures, bacteria called nitrobacter will develop and begin to convert the nitrites into nitrates. Nitrates are not as harmful to tropical fish as ammonia or nitrites, but nitrate is still harmful in large amounts. The quickest way to rid your aquarium of nitrates is to perform partial water changes. Once your tank is established you will need to monitor your tank water for high nitrate levels and perform partial water changes as necessary. There are other methods to control nitrates in aquariums besides water changes. For freshwater fish tanks, live aquarium plants will use up some of the nitrates. In saltwater fish tanks, live rock and deep sand beds can have anaerobic areas where denitrifying bacteria can breakdown nitrates into harmless nitrogen gas that escapes through the water surface of the aquarium. Many hobbyists utilize macro algae in sumps to also break down nitrates from the water.

Getting The Nitrogen Cycle Started
There are two ways to get the aquarium cycle started, either with fish or without fish.

Starting The Nitrogen Cycle With Fish
This is not the preferred way to get the nitrogen cycle started because the fish are being exposed to ammonia and nitrites during this process. Many fish cannot and will not make it through the cycling process. The fish become stressed and fish disease starts to break out or most likely the fish will just die. Certain species are hardier than others and seem to tolerate the start-up cycle better than others. For freshwater tanks, the zebra danio is a very hardy fish that many use to get the nitrogen cycle started. For saltwater tanks, some have reported success using damselfish to get the process started. Again, using fish to cycle is not a good idea and you may be wasting your money on dead fish.

Starting The Nitrogen Cycle Fishless
There are a many different ways to start the process some slower than others. The most common and effective ways are the shimp method or to use media from an existing tank.

Use Fish Food	Drop in a few flakes every 12 hours. As the food decomposes it will release ammonia. You will have to continue to "feed" the tank throughout the process to keep it going.
Use Shrimp or piece of fish	Drop a 2 inch by 1 inch chunk of raw fish or a raw shrimp into the tank. As it decomposes it will release ammonia into the tank.
Use Ammonia	Using a dropper, add 5 drops of ammonia per 10 gallons of aquarium water. If you don\'t get an ammonia reading with your test kit, add some more drops until you start to see an ammonia reading. Keep track of how many drops you\'ve used so you can repeat this process daily. Continue to dose the tank with ammonia until you start to get nitrite readings with your test kit. Once you can detect nitrites you should only add 3 drops of ammonia per 10 gallons of aquarium water, or if you added more drops originally to get an ammonia reading cut the amount of drops used in half. Continue this process daily until you get nitrate readings with your test kit. Do a 30% water change and your tank is ready.
Use material from an established tank	Use gravel and/or filter media from an established and cycled tank. This is the best and fastest way to go. This will seed the tank with all of the necessary bacteria for the nitrogen cycle. "Feed" the tank daily with flake food until you are getting nitrate readings. Depending on how fast you were able to get the gravel and filter media into your tank, you may be getting nitrate readings in only a day or two. There are some drawbacks to this method. Ask your source if they have recently used any copper medications in the tank. If they have and you are planning to have invertebrates in the tank you should probably not use this method. Invertebrates will not tolerate copper. Get a copper test kit to determine if it\'s safe to use.
Use Live Rock	The use of live rock in saltwater tanks has really taken off over the past few years. The reason for this is because it is one of the best forms of biological filtration available for saltwater tanks. The shape the rock is in when you get it will determine how long the nitrogen cycle will take. See step 7 on the saltwater setup page for more information on live rock.
Use a supplement	Use a supplement like Instant Ocean BIO-Spira for Saltwater Tanks. made by Marineland (the freshwater version may have been discontinued). This product claims to contain some patent pending species of nitrifying bacteria that will cycle your tank in 24 hours. It is kind of expensive, but if you already have fish in your tank and they are suffering through the cycle, you may want to check this stuff out. 1 ounce of this product is supposed to treat a 30 gallon freshwater tank. There are both freshwater and saltwater versions of Bio-spira. Once the cycle has started only add one or two fish at a time. Wait a couple of weeks before adding more fish. This will give your tank the time it needs to catch up with the increased bio-load.

· Speeding Up the Cycling Process
There are things you can do to speed along the process of cycling your aquarium.

o Increase the temperature of your aquarium water to 80°F-82°F (27°C-28°C)

o Get some beneficial bacteria colonies. Borrow some gravel from an established and cycled aquarium. If you have another tank with an extra filter you can use it. If you have a really nice friend with an established and cycled aquarium, ask if you can have one of their used filter media. It will be loaded with the good bacteria that we are looking for.

o There are products on the market that claim to introduce the beneficial bacteria. For more information, check out products like Bio-spira. There are many more products entering the market that contain the beneficial bacteria necessary to seed your tank. Between live rock (for saltwater aquariums) and the bottled bacteria being readily available, there really is no excuse to make fish suffer through a cycle.

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