The Nitrogen Cycle

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What is the Nitrogen Cycle?

The Nitrogen Cycle, commonly called "the cycle” or "the aquarium cycle,” is a balanced, naturally occurring process of converting organic waste into safer chemical compounds that can be reused within the ecosystem.

Beneficial bacteria converts Nitrogen compounds (ammonia, ammonium and nitrite) into nitrate, which is safer in higher concentrations.

Why is it important?

A healthy aquarium will be able to convert waste such as; fish feces, decaying plants, and deceased fauna, into nitrates (NO^3-) through the use of beneficial nitrifying bacteria. Without a healthy bacteria colony to convert this waste, it builds up in the form of ammonia, which is toxic to fish and plants even in very low concentrations.

In the natural world, bacteria thrives in waterways where theres an abundance of food and safe water levels to live in. However this is not the case for aquariums, where the water source is often sanitised to kill all bacteria.

Even though tap water is sanitised, some bacteria still survives. The bacteria can be re-established with time and a source of food

What is "Cycling" a tank?

"Cycling" a tank is the process of establishing the bacteria colony to convert ammonia > nitrite > nitrate.

It is important you cycle a tank before you add fish to it. Adding fish would produce waste and ammonia that can build up and injure or kill the fish. Similarly, adding too many fish, bigger fish, or over feeding can cause issues for newly established cycles.

The process of cycling a tank is outlined in the next few sections:

Nitrogen Cycle Breakdown

an Aquarium Nitrogen Cycle consists of 3 factors:

• Ammonia (NH^3) is toxic to fish, generally causing ammonia burns or sickness at levels below 1 ppm.

• Nitrite (NO^2-) is very toxic to fish. It causes oxygen to not bind within cells, which quickly kills fish at any significant level.

• Nitrate (NO^3-) is slightly toxic to fish and generally safe to have in the tank up to 20 ppm, depending on the sensitivity of the inhabitants

(note: this generalization applies to freshwater only)

When talking about "beneficial bacteria", we are discussing the bacteria that eat these nitrogen compounds. Nitrosomonas eat and break down ammonia, while a second bacteria type, Nitrobacter, feeds on nitrites and produces nitrates.

Ammonia is converted into Nitrites, which is then converted intro Nitrates. Nitrates are either consumed by plants, or removed via water changes.

depiction of the nitrogen cycle

depiction of the nitrogen cycle created by @suitcat

These bacteria are naturally present in all bioactive water columns, but they need food to consume, surface area to live on (e.g. the filter, substrate), and oxygen. With those three things, the bacteria will grow, and the nitrogen cycle will complete itself.

Step by step: How to cycle your aquarium

Equipment Needed:

• Water Dechlorinator/Conditioner
• Freshwater Test Kit (Ammonia, nitrite, nitrate, ph)
• Ammonia Source
• Aquarium Filter

Setting up the tank

1. Set up a filter that has some sort of surface area for the bacteria to live on. There are various types of media available; however, the most commonly recommended media are: ceramic rings, filter floss, filter pads, and filter mesh.

   Important: Most filters can be damaged by running it dry, make sure you fill the tank with water before switching it on

2. Fill the tank with Dechlorinated water. Follow the instructions on your dechlorinator bottle for dosage amount.

   Adding more dechlorinator then needed can injure and kill fish. Only dose according to the instructions

3. Add an ammonia source to the tank. This can be something that produces ammonia, like fish food, or simply use straight ammonia in small doses. Follow the dosing instructions on the label.

   avoid exceeding more then 2ppm Ammonia in the tank during cycling

4. Test the ammonia levels. If cycling with bottled or aquarium ammonia, you'll be able to test for ammonia within two hours of dosing. If using fish food, it will take 2-3 days for it to begin to decay.

   Breaking down food with a water and a syringe helps it decay into ammonia quicker

When do I add more ammonia?

Add ammonia or fish food to the aquarium each time that ammonia levels drop detectably.

For a properly stocked aquarium, you will typically need to cycle to a bioload of up to 2 ppm ammonia within 24-48hrs; therefore, we recommend making sure your bacteria can withstand the expected bioload of your given stocking.

You should be testing daily during cycling, monitoring your ammonia, nitrite and nitrate levels

Once nitrates appear, dose less ammonia product until the ammonia and nitrites turn to 0 ppm. Too much ammonia will overwhelm the bacteria, causing the ph to drop and the cycle to stall.

Dose to your original stocking amount. If using fish food, make sure you're adding more than you expect to use each day to properly account for extra ammonia output. If using pure ammonia, dose up to around 2 ppm.

When Is my cycle complete?

A cycle is technically complete when your ammonia product has successfully turned to into nitrite, then into nitrate. However, a cycle exists on a spectrum.

Your cycle needs to be able to process the amount of ammonia that will be present in your aquarium from a full fish stocking, feeding, decay and waste.

as a general rule, 1-2ppm ammonia being processed in 24 hours is sufficient for most smaller freshwater fish.

It's time for fish! Almost.

Your aquarium is now cycled; congratulations!

Keep in mind that nitrate levels have risen to a toxic level by now, so begin doing 50% temperature-matched, dechlorinated water changes every 24 hours until nitrates read below 20 ppm, then you can add fish! Get familiar with water changes anyway; they're your first line of defense against disease.

"Fish in Cycling"

"Fish in Cycling" is the act of using fish as the ammonia source to feed the bacteria. This process subjects fish to toxic levels of ammonia, and should only be completed in emergency situations. See the article Fish-in Cycling for more information.