Denitrification How to Lower Aquarium Nitrates With Denitrifying Bacteria

How to Lower Aquarium Nitrates With Denitrifying Bacteria

Nitrate can be naturally removed from aquariums with denitrifying bacteria. A 3-inch deep substrate will create an oxygen-free zone that allows anaerobic bacteria to convert nitrate into nitrous oxide and nitrogen gas. These gases then escape the tank into the atmosphere.

In this article we will explore how denitrifying bacteria works and how you can promote the growth of it inyour aquarium.

The traditional method for lowering nitrates

How do aquariums get nitrate in the first place?

Fish poop, decaying plants, uneaten fish food and other organic materials produce ammonia, a highly toxic chemical that harms fish.

Established aquariums have beneficial nitrifying bacteria (nitrosomonas) that use ammonia as a food source, converting it into nitrite. Another type of bacteria (nitrobacter) uses nitrite as a food source and converts it to nitrate.

What happens to nitrate?

In most aquariums, there is no natural system for removing nitrate. Therefore, the concentration of nitrate continues to rise over time.

Why is nitrate bad?

High cencentrations of nitrate may cause muscle tremors, disfiguration and immunity problems. Prolonged exposure to high concentrations of nitrate is known to cause death in fish.

How do you remove nitrate?

Most fishkeepers must perform water changes because their tank has no natural system for removing nitrate. The overall nitrate concentration is safely lowered by replacing a percentage of the tank’s water with fresh dechlorinated tap water.

The natural method for lowing nitrates involves dentrifying bacteria

What many fishkeepers don’t realize is that there is a natural process for removing nitrates from their aquarium without water changes. This process involves denitrifying bacteria, also known as anaerobic bacteria.

What is denitrification?

Denitrification is the process of reducing nitrate (NO3) and nitrite (NO2) into gaseous forms of nitrogen, such as nitrogen gas (N2) and nitrous oxide (N2O).

What are denitrifying bacteria?

Denitrifying bacteria are microbial life forms that are responsible for making denitrification happen. They use the nitrogen in nitrate and nitrite to harvest energy from food sources.

How denitrifying bacteria remove nitrate and nitrite from aquariums

How denitrification works

What happens during denitrification is these bacteria breathe in nitrate and nitrite and use its nitrogen too extract energy from carbon-based food sources.

Carbon food sources, such as detritus and decaying plant material, contain energy that the bacteria can consume to grow and reproduce. But this energy is trapped within these carbon compounds.

In order to extract this energy, a process called oxidation is required.

What is oxidation?

Oxidation is a chemical process where electrons are moved from one compound to another.

The compound that receives electrons is called the oxidizing agent and is being reduced. The compound losing electrons is the reducing agent and is being oxidized.

Energy is transfered through this electron exchange. This energy is used by the denitrifying bacteria.

This electron transfer causes these compounds to change their chemical composition. They are essentially being converted into something different.

Nitrogen is used as an oxidizing agent

During denitrification, the nitrogen in nitrate and nitrite is what attracts electrons from the bacteria’s carbon food source. In this reaction, nitrogen is the oxidizing agent and carbon is the reducign agent.

This is different than the nitrification process where the nitrogen from ammonia and nitrite are the food source that are being oxidized. In this reaction, oxygen is the oxidizing agent and nitrogen is the reducing agent.

Nitrate and nitrite are converted into nitrogen gas and nitrous oxide

Nitrate and nitrite are reduced into nitrous oxide and nitrogen, both gases, which will float to the surface of your tank and escape into the atmosphere. This is the end of the process whereby nitrate and nitrite are removed from aquariums in a natural way.

How do you promote the growth of denitrifying bacteria?

Growing denitrifying bacteria is less common in typical aquariums because they do not contain suitable environments for this type of bacteria to live.

Here’s why:

Denitrification requires an anoxic environment

As we now know, the process of oxidation requires an oxidizing agent. The most effective ozidizing agent in nature is oxygen. There are other less effective oxidizing agents such as nitrogen and sulfur.

But these secondary oxidizing agents will not be usued when an environment contains oxygen.

For denitrification to occur, nitrogen must be used as the oxidizing agent. This means the environment cannot contain oxygen, otherwise a different oxidising process will occur.

Environments with little to no oxygen are called anoxic.

Create an anoxic environment with deep substrate

A substrate that is about 3-inches or deeper is the easiest method for creating an oxygen-free environment in an aquariums.

As you go further down into a substrate, it becomes more diffficult for oxygen to penetrate. Eventually, after approximately 2-inches or so beneath a substrate’s surface, there will be no more oxygen.

In this environment, denitrifying bacteria will have a chance at growing because oxygen is no longer available to be used as an oxidizing agent.

But there is another requirement:

Provide a carbon food source

The other requirement for growing denitrifying bacteria is providing them with food. This will come in the form of detritus, decaying plants and other organic material that, over time, sifts its way down into the bottom layer of your substrate.

It will likely take several months for this to happen. So it’s important not to gravel vacuum during this period to allow your tank’s organic materials to find their way to the bottom.

Ryan Ferguson

Founder, Rooted Tank

Ryan Ferguson, the founder of Rooted Tank, started fishkeeping in 2019. He has continued to level-up his planted aquarium skills and wanted to share his journey and knowledge with other aquarists.


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