Category Archives: Nitrite

Everything You Need to Know About Nitrites

Nitrites – A Tenth the Level of Ammonia is enough to Kill.

i.e. 3.0 ppm ammonia is as deadly as 0.3 ppm nitrite.

Nitrites: Second Waste product in the Cycle, Low Numbers KILL!

Nitrite is an intermediate metabolite in the CYCLE. Nitrite binds fish Red Blood Cells causing gasping and “brown blood disease”. Extension agents without testing gear can make a presumptive diagnosis of Nitrite poisoning by simply cutting a catfishes’ head off, and the blood will be brown.

Fish that die with their gills flared, usually died of Nitrite induced “met-hemoglobin-emia”
Ways to combat nitrite intoxications are as follows:
1) Know the problem exists, a simple test will tell.
2) Partial waterchanges will lower Nitrite levels
3) Addition of salt (non iodized 1 teaspoon per gallon all at once) will inhibit uptake of Nitrites. (Preferred)

Interestingly, the protective function of salt lasts maybe 3-6 weeks.

If you’ve got Nitrite problems, then that means you DON’T have enough Cycle bacteria –  so if you can, BIOSEED!

4) Methylene Blue at bottle doses may also help, but not entirely reverse the Met-Hemoglobin-emia.
In many instances, the filter needs cleaning or upgrading.
Feeding should be suspended or reduced.

If you are running a drip irrigation water replacement system (CLICK), you will not need to worry about Nitrites.

Article Number Two on Nitrites

Nitrites – Brown Blood Disease

The Cycle of beneficial ammonia reducing bacteria in aquatic environments
The Cycle of beneficial ammonia reducing bacteria in aquatic environments

Ammonia is converted into Nitrite by Nitrosomonas
So, when you set up a new pond, and the fish produce Ammonia; that ammonia is reduced to Nitrite, the subject of this article.

Nitrite is converted into NitrAte (plant food) by Nitrobacter.

Nitrites cause reddening of the fins and irritation of the gills, gasping + excess mucus. A simple test kit can detect Nitrite.

Nitrites also bind the fish Red Blood Cells resulting in suffocation and “Brown Blood Disease”.
-> Nitrite toxicity is temporarily reduced by the addition of salt at one teaspoon per gallon of water.

Nitrites can be created from Nitrate under anaerobic conditions. (Deep sand, clogging filters, stalled sand filters etc.)

Nitrites can be controlled with wet-dry filtration, constant replacement of a little water all the time to the tune of ten percent per week, and traditional water changes as needed.

Nitrite toxicity is weakly reversed by addition of Methylene Blue.
+ “The reversal of Nitrite poisoning by salt is not permanent. Work at Auburn University showed the protection varied among fish species and could last up to eight weeks.” ~ Doc Johnson

+ Note From Doc Johnson
“When I have Ammonia or Nitrite problems, one of the first things I do is raise the Total Alkalinity of the pool with baking Soda, ph pills, Neutral Regulator, Oyster Shell, or similar. Then I will suspend feeding and increase aeration until the numbers come down.” ~ Doc Johnson

+ Nitrite accumulations with certain kinds of filters can be due to common undersizing mistakes. It may also be that you’re not giving sufficient oxygen or Calcium to the beneficial bacteria living in your filter. Before you get too frustrated with your filter, make sure you get some calcium carbonate for it.

Nitrites: Nitrites’ll Kill Some Fish, There’s a Test

Where do Nitrites Come From?

Ammonia is reduced by a bacteria called “Nitrosomonas” into Nitrite. These Nitrites are toxic at very low levels. People often test 0.25 (a quarter) part-per-million of Nitrite and disregard it as a problem. “Oh, that’s not enough Nitrite to matter!” they say. Perhaps they are fools. Their fishes’ health problems never end. Not until they reduce the Nitrites to conventionally immeasurable levels. Sure, there are tests which can detect traces of Nitrite at all times. That’s normal. But what you’re looking for is a “negative” result with the commercially available Nitrite test kit.

Lemme restate that. If you use a crude test kit and get any decent level of Nitrites, it’s a big deal. 0.25ppm is a lot. If you use a stealth-CIA-elite Nitrite test kit and get a parts-per-billion result, nevermind that. With a crude test kit like a “dip strip” all you need is “any” and you’ve got an issue. Bioseeding works FAST on that. There’s an article on bioseeding here in

If you find Nitrites in a recently-populated system, it’s pretty normal. The bacteria which will eventually colonize your filter and the surfaces of the pond-bottom will not have had time to colonize.

Bioseeding works.

If you find Nitrites in a well-established older system, it usually means the filter is being deprived of sufficient oxygen and / or the filter is clogged with organic waste products. The filter media should be gently cleaned with pond water and you should make sure the filter is sized correctly to your fish load.

Nitrites hurt the fish two ways. First, the nitrites are caustic (they burn) the fishes’ skin. Also, the Nitrites pass into the fishes bodies through the gills and create a damaging bond with the red blood cells. The situation is called met-hemoglobinemia wherein the red blood cells can no longer carry oxygen. The blood runs brown instead of red. The fish dies shortly after this.

Did you know that you can slow (and even STOP) the absorption of Nitrites from the water with salt?

If you use as little as one pound of non iodized table salt, or regular fish-safe salt per one hundred gallons, it interferes with the passage of Nitrite back into the fishes’ gills. This effect is not permanent but usually lasts long enough for the beneficial bacteria to populate your filter and bio-film and reduce the Nitrite.

When nitrite levels are very high, a partial water change is also helpful if it’s possible to do.

You’ll read about methylene blue being used to stop Nitrite intoxication. This is because veterinarians used to use methylene blue in cows for nitrite and nitrate poisoning. They’d inject it into the cow intravenously. I guess someone thought if it worked for cows it would have to work in the water with fish. No, it doesn’t. Save yourself the trouble.

SHORT AND SWEET: Nitrites “pop up” just after the Ammonia begins to decline in the water and are best controlled with limited salt application, OR partial water changes, and a bacterial adjuvant.