The Aquarium Nitrogen Cycle

aquarium nitrogen cycle

Hey Salty Nation, Jeff Hesketh here and I love to share information that helps fellow hobbyist be more successful in their aquarium keeping ventures. When it comes to setting up a new aquarium the first hurdle hobbyist need to jump is the aquarium nitrogen cycle.

The nitrogen cycle is the single most important process that all aquariums must through in order for them to become established and be able to support life. During this process, beneficial bacterial colonies begin to bloom and help keep aquariums in a stable state. The nitrogen cycle is the rate of which toxic compounds are introduced into the aquarium equals the rate at which they are converted into less harmful compounds. In this article we will discuss the nitrogen cycle and how to cycle a fish tank.

For more information on setting up a saltwater aquarium visit our saltwater aquarium setup section.

The Aquarium Nitrogen Cycle Step by Step

The aquarium nitrogen cycle is the rate of which toxic compounds are introduced into the aquarium that equal the rate at which they are converted into less harmful compounds which can be removed through water changes. Lets take a look at the nitrogen cycle, step by step.

Step 1: Ammonia has to be present in the aquarium. Examples include decomposing organic waste, such as fish waste, decaying plants, and uneaten fish food. Respiration and other biological processes also produce ammonia.

Step 2: Oxygen-loving bacteria  convert the ammonia to nitrite. Nitrite is toxic to fish, but less so than ammonia.

Step 3:The Nitrobacteria species of bacteria then convert the nitrite to nitrate. This byproduct of the nitrogen cycle is generally considered harmless to aquarium fish at low levels. Algae and plants then utilize the nitrate to naturally lower nitrate levels.

Step 4: Once the initial “cycling” process is complete, the beneficial bacteria have reached a population large enough to efficiently process existing levels of nitrogen waste products.

Stages of the Nitrogen Cycle

Stage 1: Ammonia is 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.

Stage 2: Soon, bacteria called nitrosomonas will develop and they will oxidize the ammonia in aquariums, essentially eliminating it. The byproduct of ammonia oxidation is Nitrites. So we no longer have ammonia in the tank, but we now have another toxin to deal with – Nitrites. Nitrites are just as toxic to tropical fish as ammonia. If you have a test kit, you should be able to see the nitrite levels rise around the end of the first or second week.

Stage 3: Bacteria called nitrobacteria will develop and they will 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.

The Aquarium Nitrogen Cycle Video with Dr. Tim

Starting The Aquarium 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 can not and will not make it through the cycling process. Often times the fish become stressed and fish disease starts to break out. Certain fish species are hardier than others and seem to tolerate the start-up cycle better than others. Again, using fish to cycle is not a good idea unless you are using Dr. Tim’s products “Fish defense” and “One and Only” which make the aquarium safe to add fish quickly. See the video below.

Visit Dr. Tim’s Website Click here to visit DrTim’s Aquatics, LLC

Better Yet Fishless cycling

There are a few different ways to conduct fishless cycling.

Using 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. I used this method on my second saltwater aquarium with great results.

Use a small piece of raw fish or a raw shrimp 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. Used this method on my first saltwater aquarium and it worked very well for me.

Seeding the aquarium with live rock or gravel from an established aquarium. This will jump start the aquarium nitrogen cycle. 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. The most common drawback to this method is inheriting aquarium pest from the donor aquarium. Its important to know exactly what your are getting.

For more on fishless cycling follow the link.

Starting The Aquarium Nitrogen Cycle without Fish with Dr. Tim

Visit Dr. Tim’s Website Click here to visit DrTim’s Aquatics, LLC


Thats going to do it for our article on aquarium nitrogen cycle if you have any questions feel free to contact me using the contact form in the main menu. For more information on setting up your own saltwater aquarium check out our start here page.

My Newsletter.

I would like to invite you to subscribe to my newsletter, it’s a great way to stay up to date on newly added content to Mad Hatter’s Reef as well as exclusive content that you can not find here on the blog.

I Appreciate You!

I just wanted to wrap things up by saying that I’m here for you. I want you to succeed as you begin with your saltwater aquarium efforts. Feel free to contact me. I will do my best to respond to your emails and answer any questions you my have about getting started with your saltwater aquarium.

Thank you so much for your support and I would love for you to drop me a line on my Facebook Page. I look forward to meeting you.

P.S. If you found this page helpful, please hit the like button below.

Be the first to comment

Leave a Reply

Your email address will not be published.