Nitrogen Cycle Guide

Establishing the Nitrogen Cycle in your new aquarium is the single most important step toward successful fish keeping, although you may not hear about it in the pet shop.

Why is the Nitrogen Cycle so important?

Because most living things produce toxic ammonia when they eat, grow, breathe and drink. People can shower it away or flush it away, but an aquarium fish has to live in a closed environment. What goes in the aquarium stays in and will poison the fish if it’s not removed or converted to something harmless. That’s where the Nitrogen Cycle comes in.

We call it the Nitrogen Cycle because toxins like ammonia (NH3), nitrite (NO2) and nitrate (NO3) are nitrogen compounds, and that’s all the chemistry words we need for now. Another important set of words is “itty bitty bugs”, which some people call bacteria. Little bugs (bacteria) are everywhere, and some of them are very good for your aquarium. In fact, different kinds of bugs eat the toxic ammonia, nitrites and nitrates that get put into the aquarium by the fish, uneaten food, dead plants and the occasional curious cat. When your aquarium has enough good bugs, they will convert all the toxins so that they are no longer harmful to your fish.

How do you start the nitrogen cycle?

The good bugs are already present in your aquarium. All you need to do to start the Nitrogen Cycle is feed them and give them a few weeks to grow BEFORE you add fish. The reason for this is that you need a large enough colony of good bugs in order to fight off the bad toxins that will be introduced when your aquarium inhabitants eat and poop.

To get your first bug (good bacteria) colony growing, you need to feed them ammonia. Your source of ammonia can be one of the following:

1. Fish flake food.
2. Adding small “starter” fish to your tank.
3. Ammonium chloride

How can you speed up the Nitrogen Cycle?

The good bacteria live mostly in the substrate (gravel or sand) and filter elements. If you have an old filter or gravel from an established (and healthy) aquarium, try to use some in your new aquarium. If you don’t have an established aquarium or know someone who does, you can also try one of the “beneficial bacteria” products such as Seachem Stability. By adding a live bacteria colony from an established aquarium or a bottle, you may be able to speed the Nitrogen Cycle in your new aquarium. However, the process will still take some time.

While all those good bugs are growing, the main task for the aquarist is to wait a few weeks. The wait gives you an opportunity to get a test kit to measure at least ammonia and nitrite, and to do some research on the species of fish you want to keep because they all need different things (water temperature, diet, environment, school size, etc.). During this time, you can add plants and operate the light and filter, but NO FISH YET.

How do you know when you can add fish?

After all that difficult waiting, you can test the water for ammonia, nitrite and nitrate. The Nitrogen Cycle is not complete until ammonia and nitrite concentration levels stay at 0 and nitrate stays below 40 ppm.

• Ammonia = 0
• Nitrite = 0
• Nitrate < 40ppm

When measurements stay at the above limits for a couple of days, the nitrogen cycle is working and the aquarium is ready for fish. As you add fish, the colonies of bacteria will grow just enough to handle the toxins. However, they can handle only so much, so don’t overwhelm them by adding too many fish or too much food too soon. Try to start stocking your aquarium slowly so that the bacteria colonies have time to grow as you add more aquarium inhabitants.

If everything works like it should, you’ll have a well balanced aquarium. To maintain that balance, change 25 or 30 percent or so of the water every week, and don’t forget to use a good water conditioner.

Hopefully this has easily explained the importance of cycling your tank before stocking it. Happy fish keeping!