High Nitrite Levels In Fish Tank

high nitrite in fish tank

Nitrite in the fish tank is usually the cause of high ammonia. As the byproducts of the fishes are decomposed, it develops ammonia in the tank. Ammonia is hazardous for the fishes and gives way to high nitrite in the fish tank. Nitrite is equally hazardous for the fish’s body and in some cases, can even cause the death of the fish. It is termed as the most lethal and toxic chemical in the fish tank.

Generally, anything below two ppm is considered to be safe in a fish tank, and nitrite level above two ppm is considered seriously detrimental for the fish. However, this does not mean that below two ppm nitrite levels in the fish tank should be left unchecked since, in the coming future, this may become wreaking havoc for the fish.

Since ammonia is considered as the first stage of nitrite development in the fish tank, it becomes essential to focus on lowering or preventing ammonia development in the fish tank.

One can always go for a nitrite test to check the nitrite level in a fish tank. When the nitrogen filter present in the tank is properly working, it converts the nitrite in the fish tank into harmless nitrite. However, this nitrite should also be removed from the tank in no time to prevent nitrite development in the future.

Now, to fix the nitrite in the tank, one needs to have an understanding of the fundamental reasons for the nitrite level high in a fish tank.


Nitrite is a waste product that develops during the ongoing biological filtration process. Now, what happens is that the bacteria produced during this natural filtration process, converts the harmful ammonia into even more dangerous product, that is, nitrite.

Firstly, it is a known fact that a new tank takes some time to produce an adequate amount of beneficial bacteria. This bacteria further take its own time for getting multiplied. Thus, in the beginning, the tank is unable to check the toxic nitrite development. Also, a weak or damaged biological filter causes hindrance in converting the nitrite into harmless nitrite. In this case, the nitrite remains in the fish tank unchecked and continues to affect the fish.

Now, an increase in the number of fishes in the fish tank or large fishes is also responsible for the level of nitrite high in a fish tank. In these conditions, the fishes give out various byproducts through excretion, which further decomposes to produce ammonia and later on nitrite in the fish tank. Also, overfeeding can cause nitrite in a fish tank too high. When the fish is overfed, it generally excretes in the tank. It thus generates inevitable byproducts in the tank which produces toxic nitrite.

Now, by the change of water or through over-cleaning the tank, the benefitting bacteria get destroyed or washed away and thus, it is unable to fix nitrite in the tank.


Increased nitrite levels in the fish tank can pave the way for the development of a fatal disease in the fish called nitrite poisoning. Nitrite poisoning can also be referred to as ‘ brown blood poisoning ‘ since it changes the blood color into brown. Nitrite poisoning can damage the immune system of the fish and causes issues of itching, fin rot, and bacterial infections. In extreme conditions, it can even kill the fish.

  • The first prominent symptom of nitrite poisoning is the change of the gill color in fishes. nitrite poisoning causes the blood and gills to turn brown. It further leads to an increase of methemoglobin in the fish. This methemoglobin shrinks the blood capacity of carrying oxygen.
  • Now, as the fish’s blood is not capable of carrying oxygen, it causes suffocation in the fish. Thus the fish can be seen moving to the top of the tank or gathering near the outlets of the tank to escape the toxic nitrite in water.
  • Also, this high nitrite in the fish tank makes the fish listless. In some cases, if the fish is too weak, it can even die at the very beginning of nitrite poisoning.
  • The rapid movement of fish’s gills is also an alarming factor of nitrite in a fish tank too high.
  • The methemoglobin can also cause several liver diseases, gill damage and damage to the blood cells.

Thus, one needs to have a solid understanding of these primary symptoms of increasing nitrite levels in a fish tank.

Lowering nitrite in a fish tank

Although below two ppm is considered a safe level of nitrite in the fish tank, it is equally essential to get rid of it too as this deficient level of nitrite can further increase in volume and can be disastrous for the fish’s survival in the tank. Some steps for lowering nitrite are:

  • Change water in the fish tank partially every week. This regular changing of the fish tank’s water goes on to dilute the nitrite in the fish tank.
  • Some bacteria products help to fix nitrite in the fish tank. Bottled bacteria products are readily available at Amazon at very reasonable prices. API Quick Start Nitrifying Bacteria for Freshwater and Saltwater Aquarium are available at Amazon. One can pour the entire bacteria present in the bottle into the tank of 30 gallons. Now avoid changing this bacteria-rich water for several days to allow the bacteria to function properly. This bacteria converts the nitrite into harmless nitrite, thus, reducing the risk of nitrite poisoning in the fish.
  • A good filter in the fish tank helps in generating more bacteria in the fish tank. As we know that the methemoglobin produced by the nitrite poisoning can cause suffocation in the fish and prevent it from breathing, this filter can help the fish in proper breathing by increasing the oxygen levels in the fish tank.
  • Furthermore, one can also use the filter from an old and established tank. It is a common issue of a newly set up tank that it is not able to develop an ample amount of bacteria required to check nitrite development. However, a filter from an old tank can develop a large number of bacteria in very less time and thus, check the nitrite development properly.
  • Nitrite poisoning is caused due to an increase in fish excretion level. To check this nitrite level, one needs to do a nitrite test in a fish tank.

This nitrite test in the fish tank can be done when a new fish tank is set up since it is initially unable to develop adequate bacteria. Also, while adding up new fish in the tank, nitrite test should be done. Moreover, the biological filter for processing the nitrogen cycle may have failed to function correctly due to different mechanical reasons. In this case, the nitrite test in the fish tank becomes essential. Lastly, one can also go for a nitrite test in the fish tank when the fish is being medicated to avoid nitrite development in the fish tank.

  • Furthermore, one can also add some marine salt that is Sodium chloride in the fish tank. As this marine salt dechlorinates the water thus, reducing the presence of nitrite in the water. Half a tablespoon of this salt can be added per gallon. This marine salt lowers the level of methemoglobin present in the fish tank and thus, prevents the fish from taking in nitrite through its gills. However, it should be kept in mind to avoid iodized table salt.
  • Now, it is also crucial to increase the aeration of the fish tank. As we are aware of the suffocation of the fish due to lack of oxygen in its blood, increasing ventilation helps in the proper breathing of the fish.
  • The leftover food of the fish is also required to be cleared from the tank in no time since it may generate more decomposed organic matter in the fish tank.
  • If a fish is already poisoned, avoid adding any new fish in the tank during the process of treatment.
  • Lastly, one needs to follow the proper hygiene process for maintaining a healthy environment for the fish in the tank.

Thus, we now know how to get rid of nitrite in the fish tank. Notwithstanding the safe level of nitrite in the fish tank, one should always remember to do away with any amount of nitrite high in the fish tank. Nitrite is responsible for the occurrence of a fatal disease called nitrite poisoning in the fish which can cause severe damages of its liver, fins, gill, and blood cells and at times, even lead the fish to succumb to death. Thus, one should do nitrite tests in the fish tank so that the fish doesn’t die of suffocation.