Are Nitrites Bad for Fish?

For your fish to thrive and live happily in a healthy condition, there is every need for a chemical balance in your aquarium. This will provide your fish with the necessary nutrients it needs at the right dose/level.  

Nitrites are one of the by-products of the nitrogen cycle. It is known to be toxic and it comes about as a result of a conversion of ammonia by nitrifying bacteria. Nitrites are said to be toxic, does it apply to your aquarium fish?

Is nitrite good for fish?. I’m sure these and many more are some of the questions going through your mind. In this article, you’ll get to know if nitrite is good or bad for your aquarium fish.

Are Nitrites Bad for Fish?

The answer is a simple yes. Nitrites are bad for your fish and can even be fatal, it is formed as a result of the conversion of ammonia by nitrifying bacteria. The binding of nitrites to haemoglobin in the fish’s blood forms methemoglobin which is very toxic to your fish. It hinders the oxygen-carrying function of the haemoglobin throughout the body.

The methemoglobin formed cannot carry oxygen therefore, your fish can suffocate even if there is enough oxygen present in the water. The presence of a high amount of methemoglobin in the fish blood will change its blood colour from red to brown hence why nitrite toxicity is referred to as “brown blood disease.”

When the Nitrite level is above 0.75 ppm in your aquarium, it stresses your fish. At 5 ppm, it is toxic to your fish. A nitrite test should be done regularly to check if there is an increase. When you notice any, you then take the necessary steps/measures necessary to bring the Nitrite level down.

How Do You Know Nitrite Poisoning In Your Aquarium?

Nitrite poisoning is mostly discovered when you use a nitrite test kit to test for the nitrites level in your aquarium. Sometimes, there are few signs and symptoms that indicate nitrate poisoning even without the test kit.

It is important to know these signs to be able to detect poisoning should there be no test kit available. Knowing these signs will make you take the necessary steps immediately when you notice them avoid killing your fish. Some of these signs and symptoms are;

  • The colour of the gills darkens.
  • You will notice your so active fish becoming lethargic
  • Rapid movement of gills and gasping of fish can also be an indication
  • Your fish will constantly come and stay close to the water’s surface
  • The sudden death of a healthy fish.

What Causes High Nitrites In An Aquarium?

One of the best methods of preventing something is knowing what the cause is. What causes the spike in nitrite levels in an aquarium? By knowing the causes, you can do well to prevent your fish from nitrite poisoning. Most times, the spike in nitrite level occurs after the following;

  • After adding a lot of fish at a time into your aquarium.
  • It happens mostly in New aquariums for less than a month.
  • After cleaning or changing your filter or substrate or both.
  • Lack of removing dead leaves
  • When you feed your fish more than twice a day
  • Adding ice to your aquarium to cool the temperature, especially during summer.
  • Lack of dechlorination before Changing water.
  • Not removing a dead fish immediately.

All the above-mentioned causes have a single similarity which is the imbalance between nitrites and bacteria. Now that you know some of the causes, you’ll do well to prevent nitrite poisoning in your aquarium.

 How To Solve High Nitrite Level In An Aquarium

Nitrites are one of the naturally occurring ions and one of the most toxic by-products of the nitrogen cycle. Nitrite comes about as a result of the conversion of ammonia by nitrifying bacteria. Due to its toxicity to your fish, there is an urgent need for the Nitrite level to be low in your aquarium for the healthy benefits of your fish. 

In situations where the Nitrite level is at 5 ppm, it becomes toxic to your fish. What are the measures you can take to bring the Nitrite level down? Below are a few tips you can use to lower the nitrites level in your Aquarium. They are;

– Remove 30% Of The Water

You should take out 30% of the aquarium water and replace it with fresh water. This is the first step to removing the  Nitrite water. This will reduce the effect of the negative impact of the high nitrites concentration because it will dilute the water.

This water change can also reduce the ammonia concentration in the water which is the main ion that is converted into nitrite.

– Add Nitrifying Bacteria

High nitrites levels signify an incomplete nitrogen cycle, adding nitrifying bacteria should be one of your best solutions. There are a lot of bottled bacteria products on the market, you should read the labels correctly to make a good choice.

You have to carefully select which product to use. Most of the products in the market are made from cheap-grown land-based nitrifying bacteria. Using such a product will outcompete the aquarium bacterias that are not well established and then later die out. This will result in a spike in the nitrite level which is far from what was intended.

Your choice of bottled bacteria must be from a rich-grown nitrifying bacteria with all its labels and information clearly stated to avoid worsening what you are trying to solve.

– Set An Aquarium Filter

Setting a filter will yield two results as regards the nitrite level. It will improve oxygen levels at the same time create a living space for bacteria. The improved oxygen will help your fish to cope with the decreased oxygen level in their blood as a result of the nitrite toxicity.

If you have an established tank, the biological filter will come in handy because you’ll have an already thriving bacteria colony that will speed up the cycling process. This is a very effective and proven step to reducing high nitrites levels in your aquarium.

– Add Substrates

This is another proven method on how to reduce nitrites levels in your aquarium. The substrate you should add is that from an already established aquarium. Bacteria inhabit substrates, so there is a colony of them from the substrate in an already established aquarium.

Adding it to your aquarium can improve the number of bacteria, as a result, reduce the level of nitrites. This method is similar to number (3) above.


Nitrites are bad for your aquarium fish. High levels of nitrites can cause nitrites poisoning which is fatal to your fish. It mostly occurs as a result of an imbalance between nitrites and bacteria. Although it is mostly detected using a test kit, you can also detect it even without the test kit by observing your fish’s overall movement and gills.

When there is an elevated nitrites level, you can change 30% of the water, add substrates from an already existing aquarium or add nitrifying bacteria. This will bring down the Nitrites level allowing your fish to thrive happily.