Understanding Nitrogen Cycle – Saving you from heartaches

If you are one of those people who have your fish dying on you whenever you set up a new tank or after you have done your tank & filter cleaning, you really need to read this. This is about the Nitrogen Cycle and understanding it will lessen your heartaches and frustrations with keeping your goldfish alive.

Nitrogen Cycle is a very important biological process that needs to happen in order for the environment to be safe for your goldfish to live in.  It is a nitrification process by colonies of good bacteria that breaks down toxic chemical compounds to non-toxic.

Nitrogen Cycle Diagram
Nitrogen Cycle

So how does Nitrogen Cycle work?

Well say we are already keeping goldfish in our tank. We feed them, and they eat happily. After eating, they’ll pee and poop.  These fish wastes will produce the first chemical compound, Ammonia in the water. Excess fish food, rotting plants, dead occupants in the tank will decay and produce Ammonia as well. Ammonia is very toxic to fish!

That is when our first hero comes in. The Nitrosomonas bacteria feed on Ammonia and break it down to another chemical compound called Nitrite. Nitrite is also very toxic to fish!

That is when our second hero comes in. The Nitrobacter bacteria breaks Nitrite to another chemical compound called Nitrate, and this is a non-toxic chemical. However high concentration of Nitrate is harmful to fish, so it is recommended to keep it below 50ppm. Nitrate can be removed from the tank via water changes (yes, very required in fish keeping) and it’s also consumed by aquatic plants that you have in the tank.

At the point when we see the emergence of Nitrate and the cessation of Ammonia & Nitrite, we can say that the Nitrogen Cycle is complete or that the tank is fully cycled. This means that the environment is now safe for your goldfish.

But there’s a problem…

In a new tank set up, our bacteria heroes are not big enough to carry out the job. They will need Ammonia (this being their food) to start establishing their colonies and this will take some time (around 2 weeks – 2 months). These bacteria mainly build their colonies in your tank’s substrate and filter media.

So if you already have a fish in the new tank before all these bacteria colonies are in place, that poor fella will need to survive the toxicity of Ammonia & Nitrite as they build up, and with a high likelihood it’s a bye-bye.

Why do my goldfish keep dying?

This situation also applies if you wiped out the bacteria colonies of your established tank by changing 100% of the water and cleaning the substrate/filter with tap water. These actions basically remove a big portion, if not all of those valuable bacteria colonies and your tank will need to go through the whole Nitrogen Cycle again.

Now you know, so what’s next?

As you see, knowing a little bit of chemistry and a little bit of biology do help in understanding what we need to do to keep our goldfish alive.  I have only touched on what Nitrogen Cycle is. Check out this post on how to cycle your fish tank.

Share this:

10 Replies to “Understanding Nitrogen Cycle – Saving you from heartaches

  1. Great post! I didn’t realize that Nitrates and Ammonia work together the way they do and always kill my fish every time I buy fish. I’m really interested in understanding how to avoid this and keep my fish from dying. Will defiantly follow to understand more. This is great info. Thanks!

    1. Thanks so much for dropping by. Yeah.. Ammonia & Nitrite are really toxic for the fish, so that is why fish keepers need to make sure their tanks are properly cycled if they want their fish to live.

  2. What a great information site ! My daughter has been having trouble with her newly purchased gold fish and tank. We’re both new at it . Its not a big tank, 20 gal starter kit. We’ve upgraded the heater to have better control but it needs more. This will be so helpful. Thank you



    1. Hi Dale,
      Thanks for dropping by. I am happy that my post is able to provide you and your daughter with some help. All the best with your new goldfish tank!

  3. Wow, what a complex process. Yes, I have had fish die in a new tank setup. I never realised how complex the whole process was.
    Thank you for this post and informing us on what has to be done to save our pet fish.

    1. Hi Mark,
      Yeah it’s a complex but essential process that needs to happen in your tank in order for it to be safe for your goldfish. Hope it helps in keeping your pet fish alive. 🙂

  4. I didn`t realize bacteria had an important rol on the life of the golden fish in the water tank. I used to have golden fishes but, as you said, they kept dying. I`m going to wait for your next blog for more information on the matter and have a second opportunity with my water tank.

    1. Hi Ruben,
      Sorry to hear about your goldfish. Hopefully this post and the coming ones will give you some ideas on what you need to do to keep them alive.

  5. Great post, Amigo.
    Everything we can do as aquarists to enlighten those that are setting up their first tank is awesome!
    Unlike what people are told in the fish aisle there is much to know lol. Keep up the good work friend

    1. Hi Rob,
      Thanks for the visit. I agree with you that there’s always something new to learn in fish keeping. Though there are some basic foundation that we need to know, a lot is from learning & sharing among fellow hobbyists.

Leave a Reply

Your email address will not be published. Required fields are marked *

This site uses Akismet to reduce spam. Learn how your comment data is processed.