What Are The Signs Of Ammonia In A Fish Tank?

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As a fish owner, it is essential to know the signs of ammonia stress and ammonia poisoning. I personally suffered from these conditions in the past, and because I didn’t know what to look for, my fish got sick and died.

These signs indicate that ammonia has spiked in your tank:

  • Your fish swim erratically.
  • The fish hide for no apparent reason.
  • Your fish get sick frequently.
  • The fish breathe heavily and gasp for air.
  • The skin near the gills turns pink or red.
  • The fish develops red streaks and patches.
  • Your fish show no interest in food.
  • Many fish suddenly die.

As we move forward, I will elaborate on the early signs of ammonia stress and the late signs of ammonia poisoning. Then, I’ll discuss the steps you should take to save your fish, including my personal ammonia detoxifier recommendation.

Still curious? Feel free to check my complete guide on aquarium ammonia, where I discussed what causes ammonia, how to get rid of it, what equipment to use, and much more.

What Are The Signs Of Ammonia In A Fish Tank?

Ammonia poisoning occurs gradually in the average tank. You are better off maintaining an ammonia-free tank. But fish can tolerate ammonia levels ranging between 0.02 and 0.05 ppm.

They won’t like it, But you can trust hardy species to survive, at least until you cross the 0.25 ppm mark.[1] You can read more about ammonia levels in this article I wrote.

Until then, you will observe one or more of the following signs:

1. Ammonia Stress (Early Signs, Up To 0.25 ppm)

  • Swimming

Erratic swimming is one of the earliest signs of ammonia stress in an aquarium. The affected fish will swim frantically, darting randomly from place to place. 

They may also collide with the objects in the tank, not to mention rubbing against the walls and substrate. This behavior tends to stand out because it is so uncharacteristic. 

Unfortunately, factors such as stress and disease can also cause erratic swimming. You have to rule out those other factors before you blame ammonia poisoning.

  • Hiding

This is another early symptom. Ammonia poisoning causes stress in fish, and stressed fish prefer to stay out of sight. The stress may kill the fish if you don’t have suitable hiding spots such as plants and decorations.

Hiding is disconcerting for newcomers. People buy fish to observe the creatures in their natural element. There is little point in keeping your tank around when all your fish are hiding.

However, that is not an excuse to take the plants and decorations away. Hiding allows the fish to relieve some stress. 

  • Disease

Fish are susceptible to various diseases, including fin rot, ich, and velvet.[2] Like every other creature; they have an immune system that combats those diseases.

However, an Ecotoxicology and Environmental Safety study found that ammonia could suppress the immune response in Nile Tilapia.[3] 

Admittedly, their findings blamed acute ammonia exposure. Species like Nile Tilapia have the advantage of living in vast water bodies that dilute toxins.

This is why some aquarists prefer to raise fish in ponds. Ponds are too large for nonionized ammonia to grow to dangerous levels.[4]

Additionally, you can afford to reduce the number of meals during the winter in response to the fish’s falling metabolism.

Fewer meals equate to a smaller volume of waste and leftovers, which, in turn, keeps the ammonia concentration under control.

Conventional aquarium species such as bettas and goldfish are not quite as lucky because they live in small aquatic environments that allow seemingly insignificant concentrations of ammonia to cause severe harm.

2. Ammonia Poisoning (Late Signs, Above 0.25 ppm)

If you permit ammonia to accumulate unchecked, your fish will manifest advanced signs of ammonia poisoning, including:

  • Lethargy

Mildly elevated ammonia levels can induce lethargy in fish, especially when you pair the toxin with other sources of stress, such as starvation.

However, you are more likely to observe inactivity in tanks with dangerous ammonia levels. Some species will stop moving altogether. They will sink to the substrate and stay there until they die.[5]

  • Gills

Have you looked at the gills? Acute ammonia poisoning will burn the gills, turning the skin in the vicinity red. The fish will start gasping for air because it can’t breathe.

These signs are so indicative of ammonia poisoning that some people use them to diagnose the situation without a test kit.

Many people confuse ammonia poisoning with oxygen deficiencies because, in both cases, the fish will gasp and run to the surface. 

But you can eliminate the oxygen deficiency option by not only testing the oxygen levels in the water but also looking at the color of the gills. If they look like they are bleeding, you have a high ammonia concentration.

A gourami fish with burnt gills and reddish skin coloration.
  • Streaks

Red streaks and patches will appear all over the fish’s body. Experts call them ammonia burns, and they are an unpleasant sight.[6] These chemical wounds prove that the ammonia concentration has reached dangerous levels.

A sick goldfish with red patches resembling bleeding.
Goldfish with red patches and sores, suffering from ammonia poisoning.
  • Appetite

Ammonia poisoning will steal the fish’s appetite. This will contribute to the creature’s lethargy. A fish that cannot eat won’t have the energy to swim. 

  • Death

Ammonia levels higher than 0.50 ppm will kill your fish in a day.[7] Some species may survive past those initial 24 hours, but they can still suffer irreversible damage that may lead to death down the line. 

Can A Fish Recover From Ammonia Poisoning?

Ammonia poisoning is nothing to scoff at. The substance has a nonionized component that can diffuse across the gill membrane.[8]

However, fish in aquariums with toxic ammonia levels are not a lost cause. If you take the following actions, they will recover:

  • Quarantine

Take fish with ammonia burns out of the community tank. Keep them isolated and treat them with antibacterial products. The fish can recover from ammonia burns if you protect them from bacterial infections. 

In fact, you can send them back to the community tank within a few days. Fish in such situations are more likely to die from advanced infections. 

  • Water Change

One assumes that you performed a water change after moving the burned fish to a hospital aquarium. But if you don’t have the option of isolating the fish, change the water in the main tank.

Aim for 50 percent. Also, make sure you rid the water of decomposing organic matter. This is essential as rotten organisms release ammonia in large quantities. 

  • Conditioners

If your fish suffer from ammonia poisoning, you can treat the water with a detoxifier. I personally use the well-known API AMMO-LOCK (link to Amazon). Add 5 ml per 10 gallons every two days until ammonia is not detected.

I also suggest getting a water conditioner, such as the Seachem Prime (link to Amazon). Apply this conditioner to the new water whenever you perform a water change. 

The last thing you would want is to exacerbate ammonia poisoning by introducing chlorine. Conditioners will bind the toxins, making them harmless to the fish.

  • Filter

If you already have a functional filter, use activated charcoal and zeolite to add a chemical filtration component to your system.[9]

You should also avoid changing or frequently cleaning the filter media. This part usually contains nitrifying bacteria, essential in converting ammonia into nitrite.

If you do wish to clean it, it is better to wash the medium with water from your tank. Avoid tap water, as it is too clean and contains chlorine and chloramine.

  • Preventative Measures

Eliminate all the factors that allowed ammonia levels to skyrocket. That includes crowding and overfeeding. Stop feeding the fish for a few days. 

Wait until the ammonia crisis passes before you resume the fish’s regular meal plan. Then, ensure you feed your fish only the amount they can finish within two minutes.

Feeding them more than that will create leftovers, which will eventually rot and pollute the water. Your fish will also poop more, which also triggers ammonia.

How Fast Does Ammonia Poisoning Kill Fish?

People expect high ammonia levels to kill fish in a day. However, you could lose delicate species within 12 hours, especially if their situation is compounded by crowded conditions, infections, overfeeding, and other problematic factors.

It also depends on how gradual the ammonia accumulated in your tank. If it happens slowly, your fish will get accustomed to it and be more durable.

Nevertheless, if the ammonia spikes rapidly, your fish will die much faster. That usually happens when you accidentally overfeed your fish or introduce a high number of fish at the same time.

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Fish are susceptible to ammonia. That is typically a bad thing, although it also comes with an advantage. As their behavior and appearance change rapidly, it becomes pretty easy to identify the necessary symptoms.

Early signs of ammonia stress include erratic swimming and hiding. That typically happens when the ammonia is still low (usually below 0.25 ppm).

Levels of 0.25 and higher will cause ammonia poisoning.  You will see your fish breathing heavily, developing red patches and streaks. These are manifestations of ammonia burns and require your intervention.

To deal with these two situations, I suggest getting a detoxifier, as I recommended earlier. You should also conduct a 50 percent water change and isolate fish that look incredibly ill.


  1. https://www.pondexperts.ca/pond-advice-tips/ammonia-ponds-aquariums/
  2. https://www.hartz.com/common-fish-ailments/
  3. https://www.sciencedirect.com/science/article/pii/S0147651322000276
  4. https://thefishsite.com/articles/managing-ammonia-in-fish-ponds
  5. https://www.tankarium.com/ammonia-poisoning-fish/
  6. https://www.thesprucepets.com/ammonia-poisoning-1378479
  7. http://www.theaquariumwiki.com/wiki/Ammonia
  8. https://scialert.net/fulltext/?doi=pjbs.2006.2215.2221
  9. https://www.birdexoticsvet.com.au/fishamphibians/2020/6/9/treating-ammonia-toxicity-in-an-aquarium-or-fish-pond