The Nitrogen Cycle and Why It’s Important

By: Michael Phife


This is part two of how to start a saltwater aquarium. Some of this may seem redundant, but I would like to emphasize the severity of why a nitrogen cycle is vital for aquarium care. Fish CANNOT live in an aquarium without nitrogen. This seems to be a subject that not many beginners in aquatics know about, much less plan for. In regards to this, I will be explaining why the nitrogen cycle is important for life and how to start it in your aquarium.


What Is Nitrogen?

Nitrogen is one of the key elements on the periodic table, and is commonly found in nature. It helps all living things grow, reproduce, and survive. It is found all throughout nature, both on land and sea, and is the key to survival for every living organism. The Earth is approximately 78% nitrogen, which goes through both biological and physiological processes in a natural state. Nitrogen can combine with many elements to create different compounds such as nitrites and nitrates (talked about in the following paragraph), which are key components to all bodies of water. The diagram below will show you a basic demonstration on how nitrogen and the nitrogen cycle occurs underwater:

The nitrogen cycle


How to Start the Nitrogen Cycle

In the ocean (or in this article’s case, an aquarium), the nitrogen cycle is a process that requires three key elements: ammonia (NH3), nitrates (NO3), nitrites (NO2). There are several ways to introduce this into your aquarium when starting up. I will list them below in bullet point form for ease of reading:

  • Live rock and live sand – When buying live rock and live sand, they both already have live bacteria in them which is very beneficial, and almost a must when starting up saltwater aquariums. This will typically start your nitrogen cycle faster, and let the cycling finish at a faster rate.
  • Quick start chemicals – This is not my preferred way of starting up the nitrogen cycle since you are adding chemicals to your water which isn’t natural, but it does add a good source of bacteria and ammonia into the water to help start the cycle quickly.
  • Table shrimp – This method sounds silly at first, but it has been proven to be effective. Essentially you throw in raw, uncooked shrimp that you purchase at any local grocery store into your tank, and it adds natural ammonia to the water. You will typically only let the shrimp sit in the water for a day or two before taking it out.
  • Ghost feeding – This is how I normally start up freshwater tanks, but it can be done with saltwater as well, despite it taking longer. You will put a very small pinch of your flaked fish food into the aquarium and let it get caught on the filter pad. This will start filtering ammonia into the tank to begin the nitrogen cycle.
  • Live fish – This is not a preferred method of starting up the cycle in the slightest, but it is a method nonetheless. In this method, you would add a cheap saltwater fish to your tank such as a damsel or chromis since they are hardy fish, and let them add ammonia and bacteria to the water naturally. *The fish may die in the process!*


How Long Will the Cycle Take?

The nitrogen cycle will typically take anywhere from 2 to 6 weeks for saltwater aquariums. Sometimes it can differ if you have ideal parameters on start-up, along with natural carriers of bacteria to start the nitrogen cycle. You should never try rushing a saltwater tank when cycling. Many people have tried and they will all tell you that it is worth waiting it out, that way you will not come across detrimental effects later on with your aquarium. It is also important to check your water parameters every few days in order to watch gradual changes in your ammonia, nitrates, and nitrites. The parameters should start off being moderately high, and slowly fall back down on your testing throughout the week. Once all the numbers go down to zero then your tank is finished cycling. Your readings should look similar to this image below: