How To Reduce Nitrite In Aquarium-5 Ways

In order to keep the tank environment healthy we aquarists always need to be one step ahead. And handling the nitrite levels is part of the job for us. Fish waste and uneaten foods become ammonia which later is converted to nitrite and causes death to our fish. 

Sadly, we can’t avoid producing ammonia and nitrite altogether. But what we can do is, keep the level in check and reduce it whenever it gets high. From my experience, it’s one of the challenging parts of having an aquarium. And this is why I want to share what I do to reduce the nitrite levels in my aquarium. 

Keep reading to find out everything you need to know about this nitrite issue. So, let’s not waste any time and get started– 

What Is Nitrite Level and its Effect?

Nitrite level means the concentration of nitrite ions that is present in your aquarium water in dissolved form. It’s a chemical substance that is formed from ammonia during nitrogen cycling in the aquarium due to the breakdown of fish excreta, uneaten food, and other organic compounds. 

As time goes by, it starts to accumulate and increase the concentration in the tank. After a certain level, it causes nitrite toxicity and interferes with the respiration system of the fish. As a result, the fishes gasp for air and become extremely stressed. Unfortunately, If this issue goes unchecked, the fish will eventually die. 

Though some beneficial bacteria can convert it to nitrate which is less harmful to the fish. But this one is harmful too if present in higher amounts. In a way, we can say that we can’t really avoid this issue so it’s very important to regularly maintain the proper nitrate balance in the aquarium.

What Are The Acceptable Levels?

To be honest there is not an acceptable level. Yes, you heard it right! In order to keep a thriving environment for your fish tank the nitrite levels need to be zero. 

Some species of fishes can be a little more tolerant to nitrite spikes but most of the fish species cannot handle the effects of nitrite even if it’s 1 ppm only. This is why you have to make sure to check if the nitrite level is zero with the best testing kit.

Interestingly, nitrite poisoning never occurs in saltwater tanks. This is because the chloride ions present in saltwater systems out-compete the nitrite. As a result, it cannot cause stress to the fish. 

How Long Can Fish Live With High Nitrites?

If the nitrite level is unchecked the fish will initially start to develop some symptoms of poisoning. They might survive around a week in this condition. 

But if it goes very high, the nitrite poisoning can kill off all the fish within a day or two. 

Why Does Nitrite Level Increase?

These are the most common reasons that cause increased nitrite levels in the freshwater  aquarium-

  • Nitrite levels can be higher in a new tank as the beneficial bacteria that convert the nitrite, take some time to establish. It’s commonly called “New Tank Syndrome”.
  • If the filter is not working properly to recycle the waste production.
  • If the aquarium is Overstocked with fish and other livestock.
  • If the fish are overfed then more uneaten food in the tank will increase the nitrite level. 
  • If the water in the tank is not changed regularly.
  • If the filter is clogged or dirty.
  • If Improper chemical additives are added that kill the beneficial bacteria can also play a role in increasing the nitrite level.
  • An unclean tank environment also generates more nitrite such as dead plants and fish left in the tank. 

What Are The Symptoms Of High Nitrite Levels?

Look out for these symptoms below and try to reduce the nitrite level as soon as possible–

  • Increased gill movement of the fish as they cannot get enough oxygen in high nitrite levels.
  • Fish swim to the surface to gasp for air.
  • Fish become less active than usual.
  • They swim erratically or in disorientation.
  • Fish eat less food or don’t eat at all.
  • Discoloration or paleness appears in the fish’s body.
  • Produce slimes in the body
  • The fish’s immunity is weakened so they easily get infected by diseases.

5 Effective Ways To Reduce Nitrite Level In The Tank

1. Test Your Water First

The first thing I always do is, check the nitrate levels in the aquarium with a good aquarium water test kit before taking any measures. Monitoring the water levels regularly helps to prevent any issues from turning into serious problems.

Besides, different fish species have their own specific water requirements. So you have to check if all the parameters of the tank are within their preferred range all the time. This will also keep you from using excess chemicals in the water that are harmful.

2. Change Water Regularly 

This is one of the most effective ways of reducing nitrate levels. You see, both nitrate and nitrites are toxic and they are continuously being produced by the fish waste and uneaten food through the nitrogen cycle. 

During the water change, I prefer to remove 30-40% of the tank water. So with this, a good portion of nitrate accumulated gets effectively removed. On the other hand, the newly added fresh water dilutes the nitrite concentration in the aquarium even more. 

With every water change make sure to remove the excess fish food floating over the surface with the help of a fine mesh fish net. Regular removal of waste and uneaten food will improve the water quality and stabilize nitrate levels.

However, make sure to use water that is free from nitrites and use water conditioners to remove any bind nitrites from the tank so that they become inactive. Always remember that frequent water changes not only reduce the nitrite levels but also help to keep the tank healthier. 

3. Clean The Filter

With time any aquarium filter can get clogged due to the accumulation of various kinds of debris. As a result, it becomes unable to clean and remove ammonia and nitrite from the tank water and eventually, it loses all its efficiency.

So, I prefer to clean my tank filter on a regular basis to keep all my fish healthy. However, you also have to remember that, if you clean your filter too often, it will damage the filter media and also some beneficial bacteria will be lost. 

This is why you have to know the interval between each cleaning of your filter. Here’s a list of different types of filters with their cleaning intervals–

Filter TypeInterval Between Cleaning
Sponge Filters 1-2 weeks
Hang On Back Filters 2-4 weeks
Canister Filters 4-6 weeks
Undergravel Filters 1-2 weeks
Fluidized Bed Filters 4-6 weeks 

Now, here’s a step-by-step guide on how I clean my aquarium filter very easily– 

  • First, turn off all the aquarium equipment before starting to clean the filter.
  • Get a clean bucket that is only used for aquarium related works and fill it halfway with water directly taken from the aquarium.
  • Now remove the filter media from the filter and wash it gently in the bucket containing the aquarium water. 
  • Keep in mind that the filter media should never be squeezed very hard because it can kill off the beneficial microorganisms present there. 
  • Take a soft toothbrush and clean the filter housing thoroughly.
  • If your filter has impellers, make sure to check for blockages too. A clean impeller will increase the filter performance. 
  • If the filter media seems damaged then it’s the best chance to replace it while cleaning. 
  • Now that everything is cleaned up properly, reassemble the filter components and plug it back in and turn it on. 
  • For the next few hours keep an eye on the filter for any unusual noises and also monitor if it’s working normally. 

4. Increase Aeration

You see when your aquarium has proper aeration, it helps to increase the oxygen level in the water. As a result, plenty of beneficial bacteria can grow in the tank that in turn convert the nitrite into other substances which are less harmful. 

It also helps to keep the fish healthy. You can choose from several options here. For example, I prefer to have an air pump that provides enough aeration inside my tank and also makes nice bubbles. You can also control the airflow with the help of a knob.

Also, you can try a large air stone or bubble wand to improve the aeration. These things have a larger surface area that allows enough air exchange.

Besides, if your filter already has a venturi valve then it’s even better. Because this thing mixes air with the water flow and results in increased aeration inside the tank. Meanwhile, you can direct the outflow of the filter towards the surface. 

This is because more movement in the surface water will allow more air exchange. However, make sure the surface agitation isn’t too excessive. Because too much movement in the water can cause stress to the fish and disrupt the balance of the aquarium.

However, if these steps are not possible for you to take then you can use the nitrifying bacteria directly in the system. Get the best commercially available beneficial bacterial supplements that will quickly convert the toxic ammonia and nitrite into less harmful substances.

Though in this case, you have to be very patient. Because the biological way of nitrite filtration is a very lengthy process and the beneficial bacterias take time to stabilize the nitrite levels.  

5. Don’t Add Too Many Fish 

Fish wastes and uneaten foods mainly contribute to high levels of nitrates. So, when you have noticed your aquarium has high nitrite levels, then you have to refrain from adding any new fish into your aquarium. 

You see, the more fish you add, the more waste they will produce. Eventually, it will make more ammonia and nitrite. 

And at one point it will be out of capacity for the filter and it will be unable to convert them into other substances. As a result, the fish species will get stressed too much. This is why overstocking fish is never a good idea. 

However, it’s hard to tell how many fishes should be in a tank without knowing the size of the tank and the species of the fish. So, instead, you have to keep some facts in mind to figure out how many fishes you can have without increasing the nitrite levels. Such as–

  • What is the tank size?
  • What are the fish species in the tank?
  • How large do they grow?
  • Do they have enough space to swim and freely move?
  • How strong is the tank filtration system? (because more fish means more waste and requires stronger filtration)
  • Are the fish aggressive? (in this case, it’s better not to mix them with other species)
  • Are the fish compatible with your other livestock such as snails, shrimps, etc.?

For example, if you have a 30 gallon fish tank you can get up to 30 one inch sized fish. But it will eventually crowd up the tank and increase competition for food among them. So, it will be best if you have 20 one inch fish instead to allow enough free movement and less competition. 

if you have a small tank it’s best not to put large or aggressive fish. However, in a larger tank, you can get plenty of large fish but you have to keep the nitrate levels in check. 

How To Prevent The Nitrite Build Up?

Some simple activities can go a long way to prevent the buildup of harmful nitrites in your tank–

  • Avoid overstocking the fish
  • Feed them once every day (not more than that)
  • Get some live aquatic plants. (they reduce the nitrite levels)
  • Trim off the dead parts of your aquatic plants and remove them from the tank
  • Regularly clean the filter sponge 
  • Do partial  water changes every two weeks
  • Clean floating uneaten foods regularly

Read More-How to Increase Nitrates in Fish Tank

Frequently Asked Questions (FAQs)

Does Aquarium Salt Reduce Nitrite?

Aquarium salt or marine salt is basically used to maintain good fish health in freshwater aquariums. It can indirectly reduce nitrite toxicity by reducing the absorption of nitrite through the gills. For this, you can add half an ounce of aquarium salt per gallon of water in the tank.

Can Fish Survive High Nitrites?

Some tolerant fishes can survive in the presence of a little bit of nitrite but it’s not more than 1 ppm. Though they still become very stressed and get poisoned by nitrite. However, most fishes cannot tolerate the presence of nitrite at all, and if they are exposed to high nitrite conditions their respiratory system fails and they die. 

How Long Does It Take For Nitrite Levels To Drop?

Normally it takes around a couple of days or even a week for the nitrite level to decrease. However, the reduction rate can be increased by doing partial water changes. In this case, the levels will drop within 2 or 3 days.


The presence of nitrite in the aquarium is a very big problem for the fish’s health. But if you understand how it’s being produced then you can easily take some preventive measures and stop it from increasing in the future. 

If you don’t want your fish to die then you have to be very observant of the nitrite levels. Test the nitrite levels and change water regularly and half of your problem will be resolved on its own.

Though there are many other tips and tricks to prevent the rise in the level and also to detect the symptoms of nitrite poisoning. The good news is, this article will serve as a guide to reduce and prevent the rise in nitrite levels in your aquarium in the future.

Share your experience on how you prefer to reduce the nitrite level in the comments below. Don’t forget to let us know on our social media what you would like to learn about in our next article. 

Howard Parker

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