What is the Nitrogen Cycle? First, the makeup of the atmosphere contains about 78% Nitrogen. This chemical element is vital to humans; however, unlike oxygen, we can not breathe in nitrogen, and it can only enter our bodies by ingestion. The cycle of atmospheric nitrogen gas going into the soil through precipitation example, snow and rain, attracts nitrogen-fixing bacteria into plant roots. Once into the plant's roots, nitrogen fixation can happen. This stage is hydrogen combing with nitrogen to produce ammonia. When Nitrification occurs, ammonia combines with oxygen in the soil, making Nitrites (No2-). Additional Nitrifying bacteria will convert this Nitrite into Nitrates (No3-). The vegetation uses some nitrate for food and energy to grow, called Assimilation. Plants are part of the diet of animals and humans, where nitrogen enters the body. Some denitrifying bacteria are responsible for releasing the nitrogen back into the atmosphere by decomposition, allowing this continuous essential cycle: the Nitrogen cycle.

Just like the importance in nature, this cycle is equally as important in the aquarium and one of the biggest things you should know as a fishkeeper. In the aquarium, nitrogen is vital to a healthy, balanced environment, just like in nature. There needs to be a period to pass in a newly setup aquarium for this autotrophic good beneficial nitrifying bacteria to establish. You can choose to set up your new fish tank and leave it completely alone, add a tiny bit of fish food, or add fish immediately. Adding fish to an aquarium set up moments ago is not necessarily recommended unless you understand the bacteria at work in your aquarium. However, if you choose to start your aquarium after adding water, it is crucial to remember to add a water conditioner. Water conditioners help take the chlorine out of the water to allow the bacteria to form vital to your aquarium health. If you choose to do nothing and leave your aquarium alone, it will take longer. However, the process will occur naturally in due time.

If starting an aquarium cycle with fish food, a minimal amount will suffice. The theory is that the fish food will break down and produce ammonia, allowing for the nitrifying bacteria to colonize. This process works great, but be careful; putting too much fish food in the aquarium with nothing to consume can often produce unwanted effects. Same with adding fish to the tank too soon before the bacteria can correctly build-up can create a bacterial bloom. A bacterial bloom is a build-up of heterotrophic bacteria, usually known as the "bad bacteria," which is what you see in a fish tank that is cloudy and milky white.

At the beginning of cycling your aquarium, autotrophic beneficial Nitrosomonas bacteria will slowly develop (needing 15-24 hours to reproduce), feed on the ammonia, and produce Nitrite (NO2-). As the natural process continues, Nitrobacter bacteria will feed on nitrite resulting in Nitrate (NO3-). At this point, knowing the Nitrogen cycle as a fishkeeper is helpful. You can steadily track where you are in the cycling process by testing the water. If you have fish in your aquarium, having Ammonia, Nitrites, or Nitrates is never good. Still, there is no other way to remove Nitrates besides live aquarium plants and/or performing water changes. Once you see Nitrate levels go up and the nitrite goes down, you know you have a cycled aquarium.

If you ever have high levels of ammonia, nitrites, or nitrates, you should do a water change; however, knowing the Nitrogen cycle helps you understand what is going on in your aquarium. However, knowing when to do regular water changes is fundamental to keeping fish. Naturally, your ammonia and nitrites should be zero. Still, when you have nitrates in your aquarium over 20 ppm or parts per million, you should do a water change or add aquarium plants, test your water and know if you should do your maintenance weekly, biweekly or monthly. Testing your water and knowing your aquarium levels is vital to maintaining a healthy, happy, balanced aquarium.

Breaking this topic down a little farther, you might experience a cloudy tank, experienced fishkeeper or not. No matter how many water changes you do, nothing works, and your beautiful aquarium looks like you poured milk into the water. Microscopically you have autotrophic and heterotrophic bacteria, as mentioned earlier. Autotrophic bacteria are bacteria that are capable of synthesizing their food. These bacteria are collectively known as your "good" nitrifying bacteria. This bacteria is structurally smaller than its counterparts and attaches to everything with surface area in your aquarium. Slow to reproduce 15-24 hours, this bacteria is in charge of converting ammonia to nitrite and then nitrate.

On the other hand, you have heterotrophic bacteria that are the first to establish in your fish tank. This bacteria can not produce the food and energy it needs to sustain itself. This "bad" bacteria acts like the decomposers of your aquarium; this bacteria feeds on organic material like uneaten fish food or waste in your fish tank. Also, heterotrophic bacteria are responsible for creating the biofilm you see as a film on the water surface or a white "moldy" looking film on driftwood or other organic material in your tank. Biofilm is a build-up of proteins from organic matter. Sometimes you are unaware; you lose a fish or have an overload of dead organic matter in your aquarium or add too much fish food and see a milky bloom in your aquarium. There are heterotrophic bacteria in your water column and when active you will see these bacteria at work in your water column, which is the milky coloration you see. This bacteria is quick to reproduce every 15-20 minutes. However, if the food source runs out, the bloom will dissipate.

When starting a new aquarium, helps to use media, plants, or substrate from an old aquarium. Ideally, you should use material from another aquarium because of all the beneficial autotrophic bacteria attached. Once in the new aquarium, this bacteria will begin to colonize the new tank. If you add too much organic matter or fish that produce a lot of waste, the heterotrophic bacteria will reproduce faster, and the likelihood of a cloudy tank rises.

If you have fish in your aquarium, you must change the water because of the excess ammonia, but find out where the extra organic material is. These chemical processes use oxygen, the same oxygen your fish need. You might see your fish at the surface gasping for air; in fact, the oxygen might be low in the aquarium, to you might add an air stone until the cloudy phase passes. If you have a new tank with no fish, you can do a water change, stop adding fish food, turn off the lights, and wait till the bloom subsides and the autotrophic bacteria catch up with heterotrophic bacteria and it runs out of a food source.