Nitrite Poisoning In Fish (& How To Reduce Nitrites)

Last Updated on 2023-08-08

If you think that the fish in your aquarium are suffering from nitrite poisoning, then you’ve found the right article! In this article, not only will you find out how to treat nitrite poisoning, but you’ll also learn what the symptoms are, the signs of high nitrite in your tank, how to check for it, how to reduce it, and most importantly, how to prevent it from happening in the future!

So keep reading to find out everything you need to know about nitrite poisoning and how to reduce nitrites in your tank!

What Are Aquarium Nitrites?

Aquarium nitrites are a form of dissolved nitrogen in the water that are a byproduct of the beneficial bacteria in your tank consuming ammonia. Once the ammonia has been consumed by the beneficial bacteria, nitrite is created, and once that has been consumed, nitrates are created. And eventually that will be consumed as well.

What Should The Nitrite Level In Your Aquarium Be?

The nitrite level in your tank should always be 0. Anything above zero will begin to have a negative effect on your fish. While low levels may not cause nitrite poisoning, they’re still going to stress your fish, weakening their immune system and making them susceptible to a whole range of illnesses.

What Causes High Nitrites In Your Tank?

There are a whole bunch of reasons that your tank may be suffering from high nitrites. The main causes are:

Decaying Waste

One of the main causes of high nitrites in a tank is decaying waste. This comes from a variety of places, including rotten food, old plant matter, and fish waste. 

The Tank Hasn’t Cycled Properly

If you’ve added fish to a new tank too quickly, then the chances are it hasn’t gone through the ammonia cycle yet. When this happens it means there isn’t enough beneficial bacteria in the tank to deal with the ammonia, nitrite and nitrates being produced by the fish.

The Aquarium Is Overstocked

It can also be the case that your aquarium is simply overstocked. If you’ve been adding too many fish to the tank, then they’ll be producing waste much faster than bacteria can remove it.

Problems With The Filter

Sometimes it can also be a problem with the filter. Oftentimes, it can be the case that the filter isn’t strong enough to handle the amount of nitrites in the water, or that it’s already too dirty to handle anything else.

Man hand pumping out water to clean up the substrate in his aquarium. Cleaning and tiding a fish tank.

Signs Of High Nitrites In Your Tank

If you think that you’re tank has high nitrites in the tank, then you may notice the following signs: 

Algae Blooms

The first sign that the nitrites in your tank are higher than they should be is an algae bloom. The algae are going to consume the nitrites in your tank, so you’ll begin to notice green water, or film or slime growing rapidly around your tank. 

You’ve Tested The Water

Secondly, if you test the water, you may notice that the nitrites are higher than 0ppm. As well as this, you may also notice that the ammonia and nitrates are higher than they should be as well, which could indicate the beneficial bacteria in your tank are struggling to convert it.

Fish Showing Signs Of Nitrite Poisoning

And lastly, your fish may be showing signs of nitrite poisoning as well. This can often be seen through damage to their gills, as well as gasping and rapid gill movement too.

How To Test For Nitrites In Your Tank?

If you’re going to test for nitrites in your tank there are two main ways to do so. You’ll either need a paper test kit or liquid test kit. Failing that, you can also take a sample of water into a local fish store where they can test it for you.

Paper Test Kit

Paper test kits tend to be cheaper than liquid test kits. However, they’re also less accurate. To use a paper test kit, you just need to take a sample of water and add the paper strip to it. Once you do this, the strip should change color based on the nitrite levels. 

Liquid Test Kits

Liquid test kits tend to be a little bit more expensive, however, they’re a lot more accurate so it’s worth the extra money. To use a liquid test kit, you just take a sample of tank water and a few drops of the liquid tester to it and shake. 

Then when the water changes color, you place it next to a chart to see how much nitrates there are.

What Is Nitrite Poisoning?

Nitrite poisoning occurs when the nitrites in the tank become too high and start damaging your fish. It’s also known as brown blood disease as it turns blood in the fish brown. 

When your fish is suffering from nitrite poisoning, there will be an increase of methemoglobin which prevents the blood from carrying oxygen around the body. This means that if your fish are suffering from nitrite poisoning, they’ll slowly be suffocating. 

Signs Of Nitrite Poisoning In Fish

If your fish tank has high nitrites, then you may notice that your fish are suffering from the following symptoms of nitrite poisoning.

Their Gills May Turn Brown

One common sign that your fish are suffering from nitrite poisoning is their gills turning brown. This happens because the gills are becoming so damaged from the nitrites in the water.

The Fish Appear Dark Or Pale

Likewise, you may also notice that fish in your tank are appearing pale or dark as well. This is because the nitrites in the tank are draining them, so they’ll naturally look a lot less vibrant.

Trouble Breathing

You may also notice that your fish have trouble breathing, which can prevent itself in a number of ways. One of the most common symptoms is that you’ll notice them gasping or that their gills are moving rapidly. 

Likewise, you may also notice that they go to the water’s surface to breathe or that they’ll move to any water outlet where cleaner water is going back into the tank.

Rubbing Against Objects

Lastly, because your fish are going to feel like there is an infection or parasite on their skin, they’ll also rub on objects to try and remove it.

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How To Treat Nitrite Poisoning In Fish

If your fish are suffering from nitrite poisoning, then you’re going to need to act quickly in order to save them. Fortunately, treatment is actually quite simple. You’ll just need to do the following:

  • Perform a large water change.
  • Add aquarium salt to the tank.
  • Reduce feeding in the tank.
  • Improve aeration in the tank.

Here’s a little more reason why each of these is so effective.

Performing A Water Change

By performing a water change of around 30-50%, not only are you going to be removing water that is full of nitrites, but you’ll also be adding new water with no nitrites in it, which will further dilute the ppm, making it much safer for fish to live in. 

Add Aquarium Salt

Once you’ve performed a water change, the next step is to add aquarium salt to your tank. Adding aquarium salt will help block nitrite absorption in your fish which will prevent them from suffering from methemoglobin toxicity.

Reduce Feeding

You should also reduce the amount you’re feeding your fish to make sure that no excess waste is being produced in the tank. As well as reducing feeding, you should also make sure to remove any excess food from the tank until the nitrite levels become more stable.

Increase Aeration

And lastly, you should also increase aeration in your tank too. Increasing aeration will increase the amount of oxygen in the tank, which in turn will make it much easier for your fish to breathe!

How To Reduce Nitrites In Your Aquarium

If the nitrite levels in your aquarium are too high, there are a lot of things you can do to reduce them! So try the following:

Perform A Water Change

The first thing you should do is perform a water change. In cases where your fish aren’t suffering too much, remove 20% but in more severe cases, you may need to remove up to 50%.

Doing this will help dilute the remaining amount of nitrites in the tank, drastically reducing the amount of nitrite in the tank.

Clean The Tank Frequently

You should also start cleaning your tank more frequently as well. By removing decaying matter from the gravel, you’re going to reduce the amount of waste in the tank, therefore, reducing the amount of nitrite being produced.

Clean Your Filter

As well as cleaning your tank, you should also make sure you’re cleaning your filter as well. A lot of the waste that is in your tank will end up getting sucked into your filter, so if you don’t remove it every once in a while, it’s going to have just the same effect as the decaying matter in your tank.

Consider Letting Algae Grow

Algae thrive on nitrites, so if the nitrites in your tank are too high, allowing algae to grow will drastically increase the consumption of nitrites in the tank!

Add Aged Filter Media

If you have another tank, or you know someone who does, adding an aged filter media is a great way to reduce the nitrites in the tank. You’ll specifically need the biological filter, which will be full of the beneficial bacteria that break down ammonia, nitrites, and nitrates.

Use Nitrite Removers

You can also use nitrite-removing pads to help get rid of excess nitrites in your tank. As well as nitrite-removing pads, you can also try something like MicrobeLift NiteOut to neutralize the ammonia and nitrites in the tank as well.

Make Sure Your Tank Isn’t Overstocked

You should also make sure that your tank isn’t overstocked. As a rule of thumb, you should only be keeping 1 inch of fish per gallon of water. Any more than this and it will be much harder to maintain safe water parameters. 

If you think you have too many fish for your tank, then you should consider either getting a bigger fish tank or moving some fish to another tank.

Stock Your New Tank Slowly

If you have a new fish tank, then you should also make sure that you’re not adding too many fish to it too quickly. When your tank is first set up, it won’t have any beneficial bacteria in it.

So if you add too many fish too quickly, there will be nothing to break down their waste which will result in an ammonia or nitrite spike. 

Get Rid Of Plant Waste

You should also make sure that you’re getting rid of any of the plant waste in your tank as well. If you see leaves that are dying, you should remove them to stop them from producing ammonia and nitrites.


Here are some commonly asked questions people have about reducing the nitrites in their tank and nitrite poisoning in fish!

How Long Can Fish Survive A Nitrite Spike?

Fish will typically be able to survive a nitrite spike for a few days before succumbing. However, you should do everything you can to fix a nitrite spike as soon as possible, because leaving your fish in water with high nitrites is extremely painful for them.

Can Fish Recover From Nitrite Poisoning?

If you catch nitrite poisoning early enough, your fish should make a complete recovery. However, in severe cases of nitrite poisoning, it can take weeks before your fish have fully recovered again. 

Can Betta Fish Suffer From Nitrite Poisoning?

You may have heard that betta fish are hardy fish, but even they can succumb to nitrite poisoning just as quickly as other fish. So even in betta tanks you should ensure the nitrites never go above 0ppm.

Can Betta Fish Recover From Nitrite Poisoning?

As long as you catch the nitrite poisoning early enough, just like with other fish, your betta will most likely make a full recovery. However, the longer they suffered from nitrite poisoning, the longer it will take for them to recover.

How Much Nitrites Can Bettas Tolerate?

Bettas should never be placed in water where the nitrites are higher than 0ppm. Anything higher than 0ppm will be harmful to bettas, and even if it doesn’t cause nitrite poisoning it will stress them and weaken their immune system.

Why Do You Have No Ammonia But High Nitrites?

Oftentimes, especially in new aquariums, beneficial bacteria in your tank is able to handle the ammonia, but there isn’t enough to handle the nitrites. When this happens you’ll have a 0ppm ammonia reading, but the nitrite reading can still be high. This is why it’s so important not to rush the cycling of your tank!


As you can see, high nitrite levels and nitrite poisoning is extremely harmful to fish, so you should do everything in your power to stop it from happening. 

But the good news is, high nitrites are easily fixed, and if you follow the advice above, you can get your water’s nitrite levels back to a safe amount in no time!

If you liked this article, make sure to check out the rest of the website! Otherwise, have a great day!

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