Ammonia Burns in Fish

Causes, Treatment, and Prevention

Butterfly fish

AGR / Getty Images

Ammonia burns are no joke—they can quickly threaten the life of your aquarium fish and destroy the tank environment. When the level of ammonia in fresh or saltwater tanks becomes too high, this substance becomes toxic and can chemically "burn" fishes' skin, eyes, fins, and gills. If you have fish, you need to know what ammonia burns look like, where the excess comes from, and how to treat your fish.

What Are Ammonia Burns?

Ammonia burns are chemical wounds on a fish's skin, eyes, fins, and gills that occur as a result of high ammonia levels in aquarium water. Ammonia is the waste product of a fish’s protein metabolism and is excreted by their gills directly into the water. Ammonia burns can lead to potentially fatal external and internal bacterial infections, and rapid increases in ammonia can cause sudden death.

Symptoms of Ammonia Burns in Fish

Ammonia burns usually do not appear until two or three days after fish are exposed to high ammonia in their tank. Signs to look for include:


  • Red blotches or streaks
  • Ragged or frayed fins
  • Cloudy eyes

Ammonia burns show up as damage to fishes' skin, anywhere on their bodies. It may cause red areas that appear abraded, ragged fins, or even eye "burns" that appear cloudy.

Fish with ammonia burns
catsidh / Flickr / CC BY 2.0

Causes of Ammonia Burns

Several environmental factors can lead to high ammonia levels in an aquarium and, in turn, ammonia burns. These include:

  • New tank syndrome: During tank cycling in a new aquarium, the build-up of ammonia to a toxic level can occur faster than the growth rate of beneficial bacteria that break down fish waste. It is important to test the aquarium water for ammonia frequently in new aquariums.
  • Chlorinated water: Chlorinated tap water contains chloramine, which will release ammonia into the aquarium during water changes. Be sure to treat your tap water with decholorinator to remove chlorine and an ammonia neutralizer if the tap water contains chloramine.
  • Transportation: When moving fish or bringing home a new addition, toxic levels of ammonia in the transport bag or container can occur rapidly. After you reach your destination, the animals in the bags or containers must be acclimated before releasing them into their new tank, but ammonia will continue to accumulate as long as the fish are in small containers.
  • Confinement: When fish are confined to a quarantine tank for the treatment of a disease or illness, there are few bacteria present to keep ammonia in check, which allows build-up.
  • Overpopulation: If too many fish and/or other aquatic animals are added to even a well seasoned or cycled tank, the problem of sudden excess bioload overpowers the beneficial bacteria's capability to compensate.


The first step in treating ammonia burns is to immediately lower the ammonia in the aquarium water by performing a water change. Test the water using an ammonia test kit to ensure that the ammonia level has been sufficiently lowered. The next steps are:

  • Isolate affected fish that may be developing secondary bacterial infections in a quarantine tank (QT), and follow proper QT protocol.
  • Treat the fish in the QT with a quality antibiotic or antibacterial medication.
  • It is best not to treat fish in the main aquarium with antibiotics. These medications can greatly weaken and even completely kill off the biological filter bacteria, which in turn will cause new tank syndrome to occur, or result in the aquarium having to cycle all over again.

Signs of effective antibacterial treatment can usually be seen in three to five days. However, treatment should be continued until fish are eating normally, at which time it can then be returned to the main tank.

Prognosis for Fish with Ammonia Burns

If fish do not suffer severe bacterial infections following ammonia burns, then they usually recover well and can be reintroduced into the tank within a week. Fish with advanced infections or those that are exposed to rapid rises in ammonia levels may die.

How to Prevent Ammonia Burns

Ammonia is the primary nitrogenous waste product of fish and is very toxic to them if allowed to accumulate in the water. Having a good biological filter (biofilter) will break down the ammonia as it is produced by the fish, keeping them safe.

Frequent water changes are also important to maintain good water quality. In new aquariums, while the beneficial bacteria in the biofilter are becoming established, ten percent or more of the water should be removed and replaced with dechlorinated water every week. For aquariums with established biofilters, a 25 percent water change every two to four weeks is good.

There are also commercial products available through the pet and fish stores that will bind the ammonia in the water to make it non-toxic to the fish. Test the aquarium water with a test kit to determine if ammonia is present, then add the ammonia neutralizing product according to the manufacturer’s dosage recommendations if ammonia is detected.

Periodically, measure the ammonia in the aquarium to ensure it is at a safe level (preferably zero).

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.
Article Sources
The Spruce Pets uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
  1. Ip, Yuen. Ammonia Production, Excretion, Toxicity, And Defense In Fish: A ReviewFrontiers In Physiology, vol 1, 2010. Frontiers Media SA, doi:10.3389/fphys.2010.00134

  2. Aquarium Water Quality: Nitrogen Cycle. Florida Department Of Agriculture & Consumer Services.