The Nitrogen Cycle

Before you bring your new fish home, be sure your tank is “cycled.” This means, the nitrogen cycle is fully functioning in your tank. The nitrogen cycle is the process which occurs during biological filtration. I will explain the nitrogen cycle as simply as possible. Please realize that this explanation is very basic, but gets the main ideas across.

You start with waste in the tank. This comes from fish waste, uneaten food, and any decaying plant matter. This waste creates ammonia in the water which is highly toxic to fish.

Because the water in fish tanks is dechlorinated, bacteria will grow in your tank on various surfaces. As water flows over these surfaces full of what we call beneficial bacteria, the bacteria takes in the ammonia and converts it to nitrites.

Nitrites are less toxic to fish, but will still be harmful when present even in low quantities.

Now, a second type of beneficial bacteria comes in a takes up the nitrites and converts them into nitrates.

Nitrates are not toxic to fish until they have built up to around 40-50 ppm (some people advocate for a lower range, some a higher).

Then, the humans have to physically remove the nitrates by performing water changes. In planted tanks, the plants will also use some of the ammonia and nitrates.

Need some more visuals? Check out this video created by Cory from Aquarium Co-op

I HIGHLY suggest you get an aquarium water testing kit, such as the one made by API. Make sure your testing kit includes pH, ammonia, nitrites, and nitrates. I don’t know if this is standard across testing kits, but the API freshwater testing kit comes with information about what the correct parameters are for different types of fish.