How To Treat Ammonia Poisoning in Fish

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Ammonia poisoning is one of the biggest killers of fish. It’s dangerous for both freshwater and saltwater fish, but it’s especially harmful to freshwater species that are more sensitive to changes in pH or water hardness than saltwater ones.

But fear not! There are some easy ways you can monitor your tank and prevent this condition from happening in your home aquarium.

What is Ammonia Poisoning?

ammonia chemical on the sink

Sometimes known as new tank syndrome, ammonia poisoning occurs when there’s too much ammonia in your fish tank. This is a common type of chemical found in water, but it becomes toxic when there are elevated levels of it.

Ammonia itself can’t be seen with the naked eye – its presence will actually alter pH readings to make them appear lower than they really are. This may trick you into thinking you have a healthy tank, when in fact its levels are rising.

These conditions can actually be very dangerous for your pets. Ammonia in high levels poisons fish by burning their gills, skin and fins. This is extremely painful and can kill them quickly. In some cases it can also cause blindness or brain damage. Therefore, it’s important to monitor water quality and take action as soon as ammonia is detected.

What Causes Ammonia Poisoning?

Ammonia poisoning occurs when there are elevated levels of it in the tank, often due to a new pet or overstocking your tank. It can also happen because:

Fish Are Overfed

Overfeeding your fish is a quick way to elevate the level of ammonia in your tank. Not only will they be unable to process all the extra food, but they’ll also excrete waste back into the water. These waste products result in elevated ammonia levels.

If you are uncertain about how much food you should feed your fish, a good rule of thumb is to only feed them as much food as they can eat in a minute. This ensures none of it will rot and cause ammonia problems down the line. You should also remove any uneaten food after a few minutes.

For more specific information on how much to feed your fish, check out this helpful article!

Inadequate Water Circulation

Ammonia, like all toxins in the water, will accumulate if it doesn’t have anywhere to go. If there’s not much movement within your tank, harmful chemicals and organic matter can build up quickly and harm your fish. This is why you also need adequate filtration for healthy living conditions.

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A good filter can help circulate the water in your tank. This will remove harmful toxins and keep them from building up to dangerous levels. Be sure to choose a filter type and size that’s appropriate for your aquarium. For example, these filters are appropriate for tanks below 20 gallons while these might be best for tanks with large amounts of water.

Poor Fish Tank Maintenance

Ammonia can also be caused by a dirty tank or poor maintenance. When dead plants and other debris from the water fall to the bottom of the tank, they’ll begin to rot, which creates high levels of ammonia that are dangerous for fish. Fish waste and uneaten food can also contribute to the condition.

Keeping your tank clean is the best way to keep toxin levels at a safe level – one that is close to nonexistent. It’s especially important to perform regular water changes if you have a smaller aquarium as this will allow you to monitor water quality more closely. The best way to monitor aquarium water quality is by conducting frequent water testing.

Inappropriate Water Sources

Many fish owners use water from the city water systems in their aquariums. While this water is safe to drink, untreated tap water does not provide habitable water for your fish. Water treatment companies add chlorine and fluoride to city water – two toxins that can be harmful to your pets when in high concentrations.

If you’re using city water instead of tap water, make sure to use aged water – water that has been left out for at least 24 hours. This will allow the chlorine to dissipate so it won’t be as harmful to your fish. You can also use a disinfectant for city water and treat the water with decholorinator for optimal results.

Signs and Symptoms of Ammonia Poisoning In Fish

Learning to spot the signs of ammonia poisoning is crucial because it will allow you to catch this issue before it becomes dangerous. If caught early, the odds of recovery for your fish are fairly high. With that being said, common signs and symptoms include:

Redness on the Skin, Fins, or Gills  

a close up picture of a fish gills

Ammonia burns the skin and gill tissue, which causes a red rash to appear. This can also cause a bloody appearance in the fins and gills of your fish, making it more difficult for them to breathe properly.

This symptom is the most important to watch for as it’s a clear sign that the ammonia levels in your tank are too high and you should immediately increase the frequency of water changes.

Lethargy and Loss of Appetite  

Ammonia poisoning will make your fish sluggish, sickly, and unable to eat properly. It can also cause them to stop eating and behave erratically. This is because the ammonia makes it difficult for your fish to breathe, which can cause them a great deal of stress and pain.

If you notice that your fish aren’t acting like themselves, eating less, or not being as active as usual, then there’s a good chance that high levels of ammonia are present in the water.

Problems Swimming  

Ammonia poisoning can make it difficult for your fish to swim properly, which will cause them to become disoriented and lethargic. This is because they aren’t getting enough oxygen in their gills – the result of this substance’s effects on the respiratory system.

Sick goldfish swims upside down in aquarium.

If you notice that your pet fish are having trouble swimming, or are swimming in erratic patterns, then there’s a good chance that ammonia is present. This can be especially true if the fish are swimming near the top of your tank as this will make it easier for them to breathe in oxygen-rich air.

Scraping Against Objects  

If your fish starts to scrape against objects or surfaces within the tank (including rocks and other decorations), it is usually a sign that something has started to go awry.

This happens because high levels of ammonia can make your fish extremely uncomfortable. It causes severe irritation to the skin and gills of your pet, which will compel them to rub against objects in an attempt to alleviate this symptom. 

How To Treat Ammonia Poisoning In Fish

Freshwater fish are particularly susceptible to this form of poisoning because they have a very delicate respiratory system. As soon as you notice your fish gasping for air, it’s time to take action and reduce the levels of ammonia in your tank.

It is important to note that there is no way to treat the condition directly. However, if you treat the tank with medication quickly, you can minimize the damage done to your fish’s respiratory system and brain.

Perform A Large Water Change

Young man changing water in aquarium using siphon.

The best course of treatment for this form of damage in fish is by performing large water changes. If you have an aquarium with filtered water, a 20 percent water change daily will suffice. If you don’t have access to filtered water, use dechlorinated water from the pet store, or tap water that has been treated with a conditioner. Check out this list of our top recommendations!

Remember not to mix the two types of water since this will cause more problems than it solves. Once your fish have recovered, it is vital to maintain safe water parameters by frequently testing your water for ammonia. A good ammonia test kit will allow you to quickly detect excessive ammonia levels and keep them under control before they harm your fish.

Another way to prevent ammonia buildup is by performing lots of water changes. By providing your fish with ideal water conditions, you will prevent the problem from resurfacing!

Add Beneficial Bacteria To Your Tank

Another possible remedy is to introduce colonies of bacteria to your aquarium in order to help break down the ammonia. Anaerobic bacteria are highly efficient at removing this toxic substance from the environment.

There are several products on the market that contain these types of bacteria – one example is Seachem Stability. It contains several different types of healthy bacteria that will get to work right away and will keep your tank clean.

Remember to follow the directions carefully when adding beneficial bacteria to your aquarium, since improper use can cause more harm than good.

Medication is an Option

If your fish are still showing symptoms in spite of your best efforts, it may be time to use medication. There are many different medications available that will help reduce the levels of ammonia in your tank and make breathing easier for your pet.

For example, you can use an ammonia removing chemical, such as AmQuel or Ammo-Lock . These can help bind nitrogen molecules so that they are no longer toxic to your fish. Some hobbyists also use activated charcoal or zeolite proteins to filter out ammonia from their aquariums.

While effective, medication is not a long-term solution. They can cause side effects such as stress and toxicity, so you should only introduce medication as a last resort.

Fast Your Fish

Lake Kutubu Rainbowfish

When ammonia levels are high in an aquarium, another course of action that you should take is not feeding your fish for at least twelve hours. When possible, remove any uneaten food from the tank to reduce ammonia levels even further.

In most cases of poisoning, it is best not to feed your fish until symptoms have disappeared. This will minimize stress on their delicate respiratory system and prevent them from ingesting more harmful toxins.

Remember that starving a sick fish can sometimes cause additional damage if they become too weak to swim properly. If you notice them having trouble swimming, it’s time to feed them some treated food so they can regain their strength and get back to normal.

Be Patient!

One of the most important things that you can do when treating this condition is to be patient and persistent. As we have mentioned above, there are no instant fixes for this problem – it requires lots of testing and patience on your part before your fish will recover.

It may take several days, even weeks before you see an improvement in your fish’s condition. However, by following the steps above and maintaining safe water conditions for your pet, they will have a much higher chance of survival!


Ammonia poisoning in fish can be a serious problem. However, there are many ways to treat this issue while safely maintaining your tank’s water quality. Simply keep ammonia levels low and maintain healthy living conditions, and your fish will be back to normal in no time!

You should now have a good understanding of what steps you can take to prevent or treat ammonia poisoning. Remember to share this article with someone who might enjoy it, and drop us a comment if you have any questions!

Wanda is a second-generation aquarist from the sunny tropics of Malaysia. She has been helping her father with his freshwater tanks since she was a toddler, and has fallen in love with the hobby ever since. A perpetual nomad, Wanda does her best to integrate fish-keeping with her lifestyle, and has taken care of fish in three different continents. She loves how it provides a nice break from the hustle and bustle of life.

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