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The Nitrogen Cycle - The Secret to Starting Your Aquarium Off Right

Establishing the aquarium nitrogen cycle is vital to a successful aquarium. Learn how to get the nitrogen cycle started easily in your new aquarium.


When setting up their first tank, many novice aquarium hobbyists overlook the importance of the nitrogen cycle and the role it plays in having a successful aquarium. Because of this oversight, novice aquarists may experience something called "new tank syndrome." New tank syndrome occurs when an aquarium has not been cycled properly and it can lead to deteriorating water quality and the death of your fish. Symptoms of new tank syndrome may include cloudy or discolored water as a result of an algae bloom; excessive levels of ammonia and/or nitrite; and sick or dead fish. All of these symptoms can be avoided by taking the time to start the nitrogen cycle in your tank before you add any fish.

What is the Nitrogen Cycle?

nitrogen xs_20179989The nitrogen cycle, also referred to as the nitrification process or start-up cycle, is a biological process necessary to maintain the health of your aquarium. During this cycle, beneficial bacteria multiply and grow in your tank, establishing a colony that helps to remove excess ammonia from tank water. This process can take anywhere from two weeks to two months, depending on water chemistry and the size of your tank. If you attempt to rush this process or introduce fish into your tank before it has cycled completely, there could be serious consequences for your fish. At the very least your tank may experience an algae bloom and, at the worst, your fish may become sick and die.

What Happens During the Nitrogen Cycle?

In the most basic terms, the nitrogen cycle simply involves the conversion of toxic ammonia into a less harmful substance called nitrate, facilitated by beneficial bacteria. Like all organisms, your fish produce waste which accumulates along the bottom of your tank. In time this waste, along with uneaten fish food and decomposing plant matter, will break down into either ionized ammonium (NH4) or un-ionized ammonia (NH3) depending on the pH of the water in your tank.

Ammonium is relatively harmless, but ammonia is toxic to fish and even a small amount can poison your tank inhabitants. If the ammonia level in your tank becomes excessive your fish may stop eating and become lethargic, lying at the bottom of your tank or gasping for air at the surface. Other symptoms of ammonia poisoning include red streaks on the fins, body and gills. These external symptoms may be accompanied by internal damage which can lead to hemorrhaging and death.

aquarium xs_6119838The pH level in your tank will determine whether waste products break down into ammonium or ammonia. PH levels under 7 generally result in ammonium production while levels above 7 result in the production of ammonia. Once ammonia has been produced, beneficial bacteria called nitrosomonas will begin to oxidize it, thus safely eliminating it from the tank. The main byproducts of this process are nitrites, substances which are still toxic to fish. Another type of nitrifying bacteria, called nitrobacter, then convert the toxic nitrites into nitrates which are not harmful to your fish in small doses. Nitrate levels can be effectively controlled through routine water changes.

How to Cycle Your Tank

In order to start the nitrogen cycle in your tank you need to build up a colony of beneficial bacteria by providing ammonia on which the bacteria can feed. You can increase the ammonia level in your tank by dropping a small amount of flake food into the tank every twelve hours. A quicker option is to add five drops of pure ammonia per ten gallons of tank water once a day. If you have a second aquarium already set up, using some gravel or filter media from that tank is the quickest and easiest way to jumpstart the nitrogen cycle in your new tank. Since a colony of beneficial bacteria has already been established in your existing tank, transferring some of these bacteria to your new tank will speed up the process. If you choose this option, continue to "feed" the tank daily with a small amount of flake food.

fish xs_12151541While immediately introducing fish into your newly-filled tank is generally not a good idea, there is a way to start the nitrogen cycle using fish. Adding one or two fish to your tank will start the process of waste production, which will then lead to ammonia production and, thus, the start of the nitrogen cycle. Experienced aquarium hobbyists generally do not recommend this option because many species of fish will be unable to tolerate high levels of ammonia. If you choose to try this method, use a hardy fish like the zebra danio. Goldfish are also a good choice since they naturally produce higher levels of ammonia.

aquarium xs_2493614Regardless of what method you choose to start the nitrogen cycle in your tank, it is important for you to monitor the process using an aquarium water test kit. At first you should see the ammonia level in your tank rising as a result of the breakdown of waste products. Eventually, your test kit will begin to detect nitrites and then nitrates as the bacteria in your tank multiply. If you feel the process is taking too long, try increasing the temperature in your tank to 80° Fahrenheit. Once the water in your tank exhibits nitrate readings, perform a 30% water change to complete the process. Add one or two fish at first and give your tank a few weeks to settle and get used to the increased biological load. Over time you can add more fish to your tank but do not rush the process or you may experience an algae bloom.

Tips for Keeping Your Aquarium Clean and Healthy

One of the simplest things you can to do keep your tank clean and healthy is to avoid over-feeding your fish. Rather than feeding your fish a large amount of food at one time, try feeding them small portions several times a day. If you only feed your fish as much as they can consume in three to five minutes, less uneaten fish food will sink to the bottom of your tank and less ammonia will be produced.

Establishing a colony of beneficial bacteria is not only essential in starting the nitrogen process in your tank, it is also important in keeping your tank clean and healthy. Avoid changing more than 50% of the water in your tank at one time and simply change your filter media rather than completely cleaning the filter. Replacing too much water and cleaning your filter completely may decimate the beneficial bacteria in your tank which could hinder the nitrogen cycle and lead to a spike in ammonia levels.


Make Your Tank Safe for Fish Immediately  One and Only from Dr.Tims Aquatics

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Make Your New Tank Safe for Fish Immediately  One and Only from Dr.Tims Aquatics