Water testing series

part 2 - Nitrite

Nitrite - The nitrogen cycle continued

In this series so far we've discussed Ammonia - What it is, what causes it, and how to remove it. Ammonia is at the beginning of the De-nitrogen cycle and so it's best to make sure you understand ammonia before looking further into the cycle. In this guide we'll be talking about some principles which are similar to those in the ammonia guide, and to avoid hashing over the same bits of information, there will be parts of this guide where we refer you to check the previous guide. Ok lets get started.

Ammonia > Nitrite > Nitrate

As previously discussed in the Ammonia guide, The nitrogen cycle (de-nitrogen cycle) is the processes of how Ammonia is converted to Nitrite by beneficial bacteria, followed by Nitrite being converted to Nitrate by a different set of beneficial bacteria. Both compounds sound incredibly similar, and this leads to a lot of confusion when talking about parameters. Both of these chemicals are very different and interact in aquariums differently.

Nitrite (NO2 - Nitrogen + 2 Oxygen)

What is Nitrite?

Nitrite is a nitrogenous compound. It can be created through the oxidisation of ammonia in bacteria (Nitrosomonas and others). Nitrite spikes often follow ammonia spikes and are a lot more common in new aquariums. In a healthy aquarium with an established filter, Ammonia should be converted to Nitrite as quickly as it is produced.

Why does it matter?

Nitrite, like ammonia, can lead to health problems and death. Nitrite can inhibit blood from carrying oxygen, damage organs & vital tissues, and weaken immune systems (leading to further problems with disease).

Level of Nitrite ppm (Parts Per Million)


No Nitrite detected by test kits. Realistically, the only safe level.


Even levels as low as this may start to cause problems. Delicate species are first to show symptoms. Fish and inverts might start to die at these levels.


Nearly all species of fish may show signs of stress and possibly disease. Fatalities are common at these levels. Breathing may be erratic and stressed.


Extremely high! Fatalities are VERY common. Disease caused by stress very likely. Lethargic behaviour and struggling to breathe is the most apparant symptom. Permanant damage likely caused.

Symptoms of high nitrite

The only safe level of nitrite is 0. Similar to ammonia, the symptoms associated with high levels of nitrite include struggling to breathe or ‘gasping’ at the water surface. Gills may look like they’re working much faster than normal. Secondary symptoms can include signs of disease such as ulcers & bacterial infections, as a result of the immune system being compromised.

Extra info - Damage caused by nitrites

Recent investigations using danios (and other species) have shown that nitrites (in the form of nitrosamines) can act as carcinogenic agents and cause tumours on organs such as the liver 

How to prevent & treat a Nitrite problem?

Whenever you detect any Nitrite you need to act quickly! Some of the best methods of treating Nitrite spikes include;

  • Maintain frequent water changes. ALWAYS use water conditioner when performing water changes. In the case of a very high nitrite level, you can perform bigger water changes to help dilute toxicity. It's advised to stay clear of water changes bigger than 50% at once as this can lead to unstable parameters and cause more stress on fish.
  • Reduce feeding. Reducing feeding will reduce waste, and therefore reduce ammonia. Reducing ammonia will help to reduce how much Nitrite is cycling through the system.
  • Don't add any more fish. The aquarium may either not be fully cycled to support the current amount of fish, or there might be too many fish for the aquarium to handle. If either of these is the likely cause, then you should NOT add any more fish, and you may need to look at removing some of the fish from the aquarium (Always make sure your fish are going to be moved to an appropriate aquarium). Simply put, the best cure here is prevention. Research how many fish your aquarium will be able to support and be patient when stocking!
  • Make sure there is adequate aeration. It's important to make sure that there is plenty of oxygen dissolved in the water, both to sustain the filter bacteria, and also to help mitigate breathing problems associated with nitrite damaged gill membranes.

More prevention tips can be found in the Ammonia guide.

Here are some additional ways to quickly treat nitrite.

Use biological enhancers

Adding more filter boosters/ Live filter bacteria will help re-establish biological filtration, especially in any case where the filter bacteria levels may have been reduced. Filter boosters are also an essential way to introduce these bacteria in new aquariums.

Filter boosters will contain a range of different filter bacteria (strains of bacteria may vary from product to product, but generally speaking they will do the same job) to deal with ammonia and nitrite (sometimes nitrate as well). You do not need different filter boosters to deal with ammonia & nitrite separately .

Chemical Filter Media

Chemical filtration can also be used to help absorb nitrite, although different media will need to be used than that used for ammonia. It is however, worthwhile considering if you may need to use ammonia absorbing filtration media to help reduce more nitrite being produced in the future.

Extra Info - can you use it all the time?

Chemical absorbing media are always beneficial to have in stock, but how often should you use them? Overusing chemical media to remove pollutants, such as nitrite, can possibly do more harm than good. The very best way to remove nitrite (and ammonia) is to cultivate suitable levels of biological filtration. The danger of using chemical media too much is that you may limit how successful your biological filtration can be, by removing the stages needed for the de-nitrification process. 

Detoxifying nitrite

Similar to ammonia, nitrite can be detoxified by several products. Detoxifying ammonia & nitrite will help stop any damage by binding it to make it safe. Some products like Seachem Prime will detoxify ammonia & nitrite for 48 hours, whereas other products, such as JBL Detoxol, will remove ammonium from the water (therefore reducing nitrite being produced.)