Nitrogen Cycle for Everyone


If this blog had a second title, it would be “How to Not Kill Your Fish.” Please read on.

You may not hear about it in the pet shop, but establishing the nitrogen cycle in your new aquarium is the single most important step toward successful fish keeping. Why? 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 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 word is itty bitty bugs, which some people call bacteria. Little bugs 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 into plant food. Almost like magic, the good bugs get into your aquarium. All you need to do is feed them and give them a few weeks to grow BEFORE you add fish. The good little microscopic bugs will eat flake food or even small hunks of raw shrimp or fish. They live mostly in the substrate (gravel or sand) and filter elements, so if you have an old filter or gravel from an established aquarium, try to use some in your new aquarium. You may be able to speed things up by adding one of the new products that contain live bacteria. However, the process will still take some time; it is not complete until ammonia and nitrite stay ay zero measured concentration, and nitrate is below 40 ppm.

The main task for the aquarist while all those good bugs are growing 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 do some research on the species of fish you want to keep. They all need different things. You can also add plants and operate the light and filter, but NO FISH YET.

After all that difficult waiting, you can test the water for ammonia, nitrite and nitrate. When measurements stay at the above limits for a couple of days, the nitrogen cycle is working and the aquarium is ready for fish. The colonies of bacteria will grow just enough to handle the toxins, but they can handle only so much, so don’t overwhelm them with too many fish or too much food. 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.

Some tap water conditioners like Prime and Amquel will neutralize toxic nitrogen compounds for about 48 hours while still making it available to feed bacteria growth. One of these tap water conditioners will help protect the fish if you already added them before growing a nitrogen cycle. Some tap water disinfectants and conditioners cam mess up test readings, so sample and test the water just before a partial water change.