How to Treat Fish for Ammonia Burns

Butterfly fish

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Ammonia burns are no joke—they can quickly threaten the life of your aquatic animals and destroy the tank environment. If you have fish, you need to know what ammonia burns look like, where the excess comes from, and how to treat your fish.


Ammonia is the waste product of a fish’s protein metabolism and is excreted by their gills directly into the water. When ammonia in fresh or saltwater reaches a toxic level, the fish's skin, eyes, fins, and gills are chemically "burnt." Low levels of ammonia in the water can cause an increase in mucus on the skin, which can make the skin of the fish look pale, and can coat the gills, which decreases the fish’s ability to breathe through the gills. Ammonia burns also can lead to external and/or internal bacterial infections. Higher levels of ammonia can cause death.

Signs of Ammonia Burns

The effects of ammonia burn usually do not appear until two or three days after being exposed, although rapid increases in ammonia can cause sudden death in the fish. Signs to look for are:

  • Ragged or frayed fins
  • Cloudy eyes
  • Rapid gilling
  • Lack of appetite
  • Red blotches or streaks
Fish with ammonia burns
catsidh / Flickr / CC BY 2.0


Ammonia burns can occur with “new tank syndrome.” During tank cycling in a new aquarium, the build-up of ammonia to a toxic level can occur faster than the beneficial bacteria that break down fish wastes can grow. This is the first step in the nitrogen cycling process. It is important to test the aquarium water for ammonia frequently in new aquariums.

During transportation, whether purchasing fish from an online supplier or your local fish store, if preventive steps are not taken, toxic levels of ammonia in the bag shipping water can be reached in a rather short period of time. This applies just the same for the water in a transport container when packing up and moving fish as well.

During acclimation procedures, after you have reached your destination, the animals in the bags or transport containers need to be acclimated before placing them in their new home. No matter which method you choose to do this, the extended time they are in the water during the process, ammonia will continue or begin to build-up.

When fish are confined to a container for the treatment of a disease or illness, there are no good biological bacteria present to keep ammonia in check, which in turn allows it to build-up. This also applies to treating animals in a quarantine tank, because many medications will kill beneficial bacteria as well.

If too many fish and/or other animals are too quickly added to even a well seasoned or cycled tank, the problem of the excess bioload overpowers the biological filter's capability to compensate.


The first step is to immediately lower the ammonia in the aquarium water by performing a water change. Test the water using an ammonia test kit or test strip to ensure that the ammonia has been removed. 

  • Isolate the fish in a quarantine tank, 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 to have to cycle all over again.

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


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, 10 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. Use a test kit to measure the ammonia in the aquarium water to ensure it is at a safe level (preferably zero).

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. These are good to use when setting up a new aquarium, during the cycling period, and also helpful to use when new fish are added to the aquarium (which increases the bioload) or after cleaning the aquarium or filter (which can decrease the bacterial population in the biofilter). Test the aquarium water with test strips or kits to determine if ammonia is present, then add the ammonia neutralizing product according to the manufacturer’s dosage recommendations if ammonia is detected.


One other cause of ammonia burns can be from tap water that contains chloramine, which will release ammonia into the aquarium with water changes. Be sure to treat your tap water with decholorinator to remove chlorine and an ammonia neutralizer if the tap water contains chloramine.

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
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  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