Nitrite Poisoning in Aquarium Fish: What Is It?

Let's learn about "Aquarium fish". according to Wikipedia

Nitrite value testing

As a nitrogenous waste product, fish expel ammonia through their gills. Beneficial bacteria in the aquarium convert poisonous ammonia to nitrite, which is likewise hazardous to the fish. Other bacteria convert nitrite to safe nitrate in an established aquarium that has completely cycled. Ammonia may easily build up to dangerous levels in new aquariums if the bacteria population hasn't matured enough to detoxify the wastes from the aquarium's fish.

Nitrite poisoning is a significant killer of aquarium fish that follows closely after excessive ammonia levels. Just when you think you're safe after losing half your fish to ammonia sickness, the nitrite level increases, putting your fish in jeopardy once more. When ammonia levels rise, nitrite levels rise along with them. When setting up a new tank, introducing additional fish to an existing tank, while the filter fails due to power or mechanical failure, and when medicating ill fish, test the water to avoid nitrite poisoning.

  • Names: Brown Blood Disease, Nitrite Poisoning
  • Disease Type: Environmental
  • Cause / Organism: Nitrite


  • Fish gasp for breath at the water surface
  • Fish hang near water outlets
  • Fish are listless
  • Brown gills
  • Rapid gill movement

Because of the increased methemoglobin in the blood, nitrite poisoning is also known as "brown blood illness." Methemoglobin, on the other hand, presents a more significant problem than just altering the color of blood. It stops the blood from carrying oxygen, causing the fish to suffocate even when there is plenty of oxygen in the water.

Different fish species may tolerate varying quantities of nitrite. Some fish may appear to be bored, while others may die abruptly and without warning. Gasping at the water's surface, hanging near water outlets, fast gill movement, and a change in gill color from normal pink to dark brown are all common signs.

Fish exposed to even low amounts of nitrite for extended periods of time suffer immune system impairment and are more susceptible to secondary illnesses including ich, fin rot, and bacterial infections. Damage to the liver, gills, and blood cells occurs when methemoglobin levels rise. Affected fish will eventually die from a lack of oxygen and/or subsequent infections if left untreated.

Treatment of Nitrite Poisoning

  • Large water change
  • Add aquarium salt (sodium chloride) or a marine salt mix
  • Reduce feeding
  • Increase aeration

To minimize the nitrite level, first do water changes using dechlorinated water. By preventing nitrite absorption via the fish's gills, a half-ounce (1 tablespoon) of salt per gallon of water will avoid methemoglobin poisoning. You may use any aquarium salt or marine salt combination. Iodized table salt should not be used. To provide enough oxygen saturation in the water, aeration should be increased. Feedings should be cut back, and no new fish should be put to the tank until the ammonia and nitrite levels are below zero. Excess ammonia will be converted to nitrite as a result of this reduction. Daily testing and therapy must be continued until the nitrite level drops to zero.

Prevention Tips

  • Stock new tanks slowly
  • Feed sparingly and remove uneaten food
  • Change water regularly
  • regularly to catch problems early

Avoiding high spikes and chronic nitrite elevations is the key to preventing fish mortality. When creating a new tank, just add a few fish at first and wait until the tank is thoroughly cycled before adding more. As the quantity of ammonia generated by the fish rises, the number of helpful bacteria will grow. Avoid overstocking an established tank by simply adding a few additional fish at a time.

Feed modest amounts of food to the fish, and remove any food that hasn't been devoured in five minutes. Weekly, clean the tank, being sure to remove any dead plants or dirt. Perform a partial water change every other week at the absolute least, and more frequently in small, heavily-stocked tanks. After an ammonia surge, test the water for nitrite since there will be an increase in nitrite levels later. The helpful bacteria in the biofilter will gradually convert the nitrite to harmless nitrate, which should also be eliminated with frequent partial water changes.

If you suspect your pet is sick, call your vet immediately. For health-related questions, always consult your veterinarian, as they have examined your pet, know the pet's health history, and can make the best recommendations for your pet.


"Aquarium Water Quality: Nitrogen Cycle. Florida Department of Agriculture and Consumer Services", "Nitrite Toxicosis In Freshwater Fish. Purdue University", "Declercq, Annelies Maria et al. Columnaris Disease In Fish: A Review With Emphasis On Bacterium-Host InteractionsVeterinary Research, vol 44, no. 1, 2013, p. 27. Springer Science And Business Media LLC, doi:10.1186/1297-9716-44-27";