Nitrites in Aquarium – Causes & How to Get Rid of it?

Being a dedicated fish owner, I always try my best to check whether everything is in balance in my aquarium.

From food of the fish to the level of nitrites.

 Yes, you read it right, I have to check the level of nitrites too.

Nitrites in an aquarium: causes and how to get rid of them? There are bacteria in your aquarium which are responsible for turning the ammonia into nitrites but don’t worry; there is are ways to protect your fish from nitrites. Such as partial water changes, an appropriate amount of food for the fish, filter media, salt, Aeration, etc.


In this article, I will help you understand what are nitrites, their causes as well as how to get rid of them.

What Are Nitrites?

Nitrites, having the chemical formula NO2, are basically salt or ester of nitrous acid.

Nitrous acid is an unstable, week acidic compound which is prepared in the form of cold, dilute solution.

 In simpler words, nitrites are nitrogen- oxygen chemical unit.

In industry, nitrites are used as food preservation. In soil, nitrites are converted into nitrates which are then taken up by plant.

There are some advantages and disadvantages of nitrites for humans, but lets see how they affect fish.

How Are They Produced?

The Nitrogen Cycle

Here is how the nitrogen cycle works and how bacteria is responsible for the process.

The organic matter or nitrogenous waste in the aquarium is broken down into ammonia (NH3).

 Waste includes:

  • Leftover food
  • Fish waste
  • Decaying plants

Then the ammonia, because of the bacteria, is converted into nitrites (NO2-). This process of ammonia being converted into nitrites is called NITRIFICATION.

Then those nitrites are converted into nitrates (NO3-) and that too by the help of bacteria.

Nitrates, on the other hand, are used by the plant or algae in your aquarium. Nitrates are somewhat chemically similar to nitrites.


I learned it, as its basically moving from a bad chemical which is ammonia to a useful compound which is nitrates.

Meaning, ammonia, being the first byproduct, is highly dangerous.

Ammonia is highly toxic for your fish, and it prevents the fish from breathing correctly.

 Then we have nitrites, the second byproduct of the nitrogen cycle.

Nitrites are less harmful than ammonia.

 And at the end, we get nitrates which are less harmful than both ammonia and nitrites

Excess of anything is bad for humans, and the same goes for the fish.

Though nitrite and nitrate are less harmful than ammonia, still it is necessary to maintain an appropriate level.

Understanding this nitrogen cycle is really important!

 For all those who own a fish and even for those who are planning to.

Harmful Effects of Nitrites

Nitrites may seem harmless, but that cannot be further from the truth!

Nitrites are more toxic for the fish in your fish tank as compared to nitrates, which are comparatively less toxic to fish.

Nitrites are really dangerous for fish in many ways. They enter the blood of fish and oxidize the iron in their hemoglobin which results in the production of a molecule called methemoglobin.

 Methaemoglobin is unable to carry oxygen around the body.

In simple words, because of nitrites, oxygen can’t bind with the blood properly which is immensely problematic for the fish.

Wait! It gets worse.

Longs periods of exposure to nitrites make the immune system of fish, less effective.

Nitrites can even kill the fish.

 If proper preventive measures are not taken on time.

So basically the three , i.e. ammonia, nitrite and nitrate produced from organic matter, are immensely toxic for your fish, depending on the level of these byproducts.

I know, this must all seem really difficult to wrap your head around.


If you don’t ask fast, you will probably end up flushing your fish down the toilet.


How Does The level of Nitrites increase?

Before learning how to get rid of nitrites, and save the day.

You need to know why the levels of nitrites increase in the first place.

The level of nitrites in your aquarium most probably increases due to the following reasons:

  • The aquarium is new, or you have recently established it. The result can be the new tank syndrome. I will be talking about that later on in the article.
  • You have added too many fish at once.
  • Dead fish are in the aquarium and are not immediately removed.
  • Dead plant or leaves are in the aquarium.
  • You have fed the fish more than they require.
  • The Fishtank is too small.
  • Your fish tank is not appropriate for the number of fish you have.

Detection of Nitrites

If you have recently bought fish, then it will take some time for you to understand what your fish actually needs and is going through.

Even I struggled in my initial days as a fish owner.

So no need to worry!

Here are some signs that can help you know whether the level of nitrites are high and are stressing out your fish:

  • Fast gill movement
  • The Fish becomes dark or pale
  • Your Fish breath at the water surface
  • Death of healthy fish

However, there are specific nitrite tests available.

You just need to be a little attentive.

To protect your fish, you have to check the level of nitrites in your aquarium.

Ideal Level of Nitrites in Aquarium

The appropriate level of nitrites in the fish tank is ZERO.

NOT KIDDING. It should be ZERO, which means it should be at an undetectable level.

However, depending on the fish species some are more nitrite tolerant than others.

Though the ideal level is zero even its acceptable if its level is between 0 and 0.2 ppm (ml/g)

 Nitrite level 0.5 ppm causes stress to fish.

Remember this!

It is essential that everything in your aquarium should be balanced, for fish to survive even if it is the food you give to your fish.

This is because an excess of food can be dangerous as it disturbs the normal nitrogen cycle.

To maintain the zero nitrite level, it is necessary that bacteria should exist in a large amount so that they can break the nitrites, at the exact moment they are produced. This is known as biological filtration.

First of all, protect your fish!

 For that you can, merely relocate it.

Decreasing the Nitrite Level

Eliminating nitrites from your aquarium is not as complicated as it seems.

Though you need to remember, that it is highly significant that you nip this dilemma in the bud.

There are many ways you can quickly reduce the number of nitrites in your fish tank.

I have explained some of them below.


One of the solutions is partial water change.

Partial water change should be approximately 25%, in order to dilute the concentration of nitrite in water.

You should do that at least once a day, that will be enough.

However, retesting after few hours is essential.

Secondly, water change also depends on the fish type because some fish are sensitive and cannot tolerate substantial water changes.


Improve the biological filtration.

Mostly its better in the old aquariums but in new aquariums it takes some time.

Fishless cycle is well known.

The purpose of Fishless cycle is to grow bacteria in an aquarium before any fish is added to the aquarium.

 It is like replicating a natural process to provide a fish with a better environment to survive.

It takes 4 to 6 weeks for the bacteria to grow.


Now one thing that you need to keep in mind is that you cannot just simply leave the tank empty and expect the bacteria to grow on its own.

Earlier, people used to add fish in the cycle to have the desired bacteria.

 I call them fish who sacrifices for other fish.

 But this isn’t much in practice now.

There are some bottled bacteria which can also be added to break down the nitrite into nitrates, and those are less harmful.


You should provide your fish with the appropriate amount of food.

The more food you give to your fish, the more they will eat.

Overfeeding can lead to your fish getting seriously sick.

Not only that!

 Some of the food will be left uneaten.

That would result in more WASTE, which would ultimately be broken down into ammonia and eventually more NITRITES be produced.

So try not to overfeed your fish!

The best way to do this is to provide your fish with enough food that they can devour in under five minutes.

This will not only protect your fish from overeating but also decrease the amount of left-over food

So be very careful!


This method will surely work.

A filter media help to maintain an appropriate oxygen level and provide space for the bacteria to grow and thrive.

Filter, basically, sucks in the water.

After that, the water flows over the sponges (if that filter media is used).

The beneficial bacteria live and grow there.


As nitrites make deprive the fish of oxygen, air-stone can be of great help at that time. They provide more oxygen to the fish.


In saltwater, nitrites are not as toxic as they are in freshwaters.

Adding salt is another way to solve the nitrite problem because it provides chloride.

 A little amount of salt can be added, and it will prevent the nitrite from entering the blood of your fish.

But again,

The mount of salt that you add should also be appropriate as too much salt can end up damaging your whole aquarium.


Being an avid fish lover, I am more concerned about protecting my little fishy friends from the start rather than getting mad later.

So for preventive measures here some tricks.


If I buy a new fish, I make sure there is enough space for it otherwise more nitrites will begin to accumulate in small tanks. It might happen because of excessive waste of fish, over crowdedness in a small tank.


Add a limited amount of food. I feed my fish once a day but I add enough so that it doesn’t starve, neither do I overfeed them.


It would be better if you take on this responsibility of providing your fish with food or give this responsibility to any one person otherwise all the fish lovers would be adding food in the tank and the result would be worse.


It is important to maintain the plants in the aquarium and have check a on them.


If you see your plants decaying , remove them immediately because that too can increase the level of nitrite.


Just imagine what would happen if every time you clean a filter but particles of uneaten food, fish waste, and decayed plants remain inside the filter.

Those particles will be broken down into ammonia and then nitrites.

Proper maintenance of filter is important.

Sponge will surely be a good option, it will not let the particles go inside your your filter


I do not add fish to a new tank directly because bacteria needs to be established; otherwise the result will be new tank syndrome.

  • NEW TANK SYNDROME- it’s common but challenging. If there are no suitable bacteria in the fish tank, you can treat it by changing some of its water and add clean and dechlorinated the water.


You should have ample information regarding the fish, you plan to bring home.

 This is important because there are different kinds of fish like Cat Fish, Cardinal Fish, Salmon, Tuna, Hatchet Fish, etc. and they all have different needs, and their tolerance levels are also different.

So having the knowledge about the fish can not only be beneficial for you but also for your fish.


How to Test For Nitrites?

There are some nitrite tests that can make things easy for you.



For having the accurate result, go for Hanna marine nitrite checker, ultra-low range.

It gives reading in ppb, so to convert it into ppm all you have to do is multiply it with 1000.

The kit includes two cuvettes- two little tubes and battery

Add sample water in the cuvette, clean it properly with cloth and then place it inside the checker. C2 will appear on the screen.

After that take out the cuvette and add the reagent into the water, place it back inside the checker, then you will get the reading.

This nitrite checker shuts down automatically right after 2 minutes.


  • Easier to use
  • Gives you Accurate digital readings


  • Hanna marine nitrite checker is expensive



API nitrite test can detect high nitrite level from 0-5 ppm.

It contains 180 tests. Kit also includes glass test tube and color chart.

Test instructions can be found at the back of the color chart.

All you have to do is take the water sample from your aquarium and add 5 drops of test solution.

Shake it and then leave it for 5 minutes.

Now match the color of the water in the tube with the color chart.

API master test kit also includes nitrite test along with other tests.

its preferred to check the water condition of your aquarium at least once a week.


  • API nitrite test kit reads the nitrite level quiet accurately.
  • Its easily available.
  • Instructions are simple.


  • API master test kit is expansive.

If you have recently bought the fish, then it will be difficult for you to judge the result through manual checker.



Unlike other tests which suffers from amine interference, in salifert nitrite test there is no amine interference.


You can go for up to 60 tests

Instructions are available, if you will follow it properly it will be quiet easy for you to measure the nitrite level.

You have to take the sample water into a syringe, add it into a test then add a spoon of NO2 powder.

Shake the mixture, leave it for sometime and then match it with the scale.

The salifert test kit has two scales and can measure from low to high level of nitrite.


  • The kit is cheap


  • If you are using it for the first time, it will be a bit difficult for you.

Other Tests

When you know what kind of fish you have and what your fish can tolerate, you can conduct inspections of the following water parameters:

  • Ammonia
  • Nitrite
  • Nitrate
  • Gh- General hardness of water
  • Ph- for measuring the acidity
  • Kh- carbonate hardness of water


Apart from Nitrites there are many other chemicals are compounds in aquarium water that can harm your fish.


Unfortunately, heavy metals such as zinc, copper, lead, etc. in water can be a cause of sudden death of fish. It is said they are accumulated in the tissue of fish and can kill it.


As said before, nitrites and nitrates are somewhat harmful chemicals.

Nitrates are good chemicals. Having said that, they can be dangerous for the fish if the level is high.

High nitrate level is called as nitrate poisoning which can even kill the fish in the aquarium.


There are sure signs and symptoms which can help us to know that the nitrate level is high.

  • Fish remain at the bottom of the aquarium.
  • Fish don’t eat much, i.e. they don’t eat the amount of food they used to eat.
  • Rapid gill movement.

It can be treated by a small water change; sudden substantial water change can cause more harm to the fish.


Excess carbon dioxide can kill a fish.


Carbon dioxide affects the fish ability to hear, smell, etc. by interfering with the receptor of the fish’s brains.

Because of excess carbon dioxide fish start breathing rapidly. This condition can be treated by placing an air-stone in your fish tank. Otherwise, you will lose your fish.



Isn’t this surprising that same water which is treated with chlorine is totally fine and safe for human, but the same water can kill a fish?


Chlorinated water blocks the oxygen-carrying cells of fish, which causes to fish to gradually die in the water.


Hydrogen sulfide is toxic for the fish it generally results from poor maintenance.


Don’t let that colorful creature die.


What is an appropriate fish tank size? A 20-gallon fish tank is preferred for one fancy goldfish, and at least it should be 30 gallons if you want to keep two.

Are bigger aquariums better or smaller? The fact is bigger aquariums are easy to maintain than a smaller one. Secondly, fish are happier in a bigger aquarium. In small aquariums, they feel stressed.

What is the suitable temperature for fish? It depends on which species of fish you want to keep. Some are held in more warm temperature than others, but really warm temperature is not right for the fish too. Generally, 75 to 80 F is preferred. Any temperature above that can kill your fish.

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