Ammonia poisoning in goldfish: A deadly problem!

Ammonia poisoning in goldfish is one of the most common problems that goldfish owners face. In fact, every goldfish owner has probably experienced an ammonia problem at some point.

Ammonia poisoning, also known as “new tank syndrome”, often occurs when a new tank has not been installed properly.

Ammonia poisoning is the leading cause of death in goldfish tanks.

What is ammonia poisoning?

Ammonia is the main waste product of goldfish. Your fish release ammonia into the water through their solid waste and gills.

Organic matter that decomposes in the aquarium also releases ammonia. For example, ammonia is released from rotting food and dead plants.

Ammonia poisoning is when high levels of ammonia begin to harm your fish. Ammonia burns the fish’s gills and ultimately prevents them from breathing. Therefore, ammonia poisoning is fatal if not acted upon quickly.

Signs of ammonia poisoning in goldfish

Ammonia is a silent killer. It is a combination of hydrogen and nitrogen and has no color. This means you won’t be able to see it and you won’t realize there’s a problem until it’s too late.

There are two ways to know when ammonia levels are too high.

You can use a test kit to measure your ammonia levels.

Or you may notice symptoms of ammonia poisoning in goldfish.

Common symptoms of ammonia poisoning:

  • Blood streaks on tail and fins
  • Sitting at the bottom of the tank
  • Lethargy
  • Spending
  • Labored breathing
  • Decreased appetite
  • Increased slime production
  • Red spots on the skin are ammonia burns.
  • Inflamed gills

Causes of ammonia poisoning in goldfish

There is no safe level of ammonia in a goldfish tank. The ideal ammonia level in the tank is zero.

Ammonia poisoning can be caused by various reasons. This includes:

  • Don’t cycle your tank
  • Overcrowding your aquarium with too many fish
  • Overfeeding fish
  • Adding untreated tap water
  • Insufficient filtration
  • Wrong pH level
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Let’s look at each of these potential problems so you can avoid them.

The Nitrogen Cycle and Cycling Your Aquarium

In an established aquarium, healthy bacteria break down the ammonia before it harms your fish.

All the ammonia from your fish, their food, and rotting plants is effectively eaten up by bacteria and converted into less harmful substances.

Nitrosomonas bacteria consumes ammonia and releases nitrite. Nitrites are toxic to goldfish, but less toxic than ammonia.

Bacteria Nitrobacter then consumes nitrite and converts it to nitrate. Again, nitrate is still toxic, but to a lesser extent than ammonia and nitrite.

At this point, the bacteria can no longer help, and it’s time for you to work! Regular water changes are necessary to remove nitrates from the aquarium.

This process of breaking down ammonia into nitrites and nitrites into nitrates is called the nitrogen cycle.

If your aquarium is not yet on a nitrogen cycle, you will need to follow a process called “cycling”.

If you don’t cycle your aquarium, or if something disrupts your nitrogen cycle, then dangerous levels of ammonia will start to build up.


More fish = more ammonia. If you add too many fish to your aquarium, the nitrogen cycle will not be able to remove all of them and they will reach dangerous levels.

You should never add too many fish to your goldfish tank.

And never keep goldfish in a bowl or aquarium that is too small for them.

We also advise you not to load a new aquarium right away. Instead, add fish one at a time so that the nitrogen cycle has time to adjust to the increased amount of ammonia that more fish will bring in.


Avoiding overfeeding is a very simple way to avoid excess ammonia in the aquarium.

If your fish eat all their food, there will be no uneaten food left in the aquarium. This means less ammonia in the water.

This is just one of the reasons why it is important to know how often and how much to feed your goldfish.

Does not treat tap water

Tap water can contain ammonia as well as other toxic chemicals.

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Thus, you may unknowingly add ammonia to the aquarium every time you do a water change.

To avoid this, you need to treat the water before adding it to the aquarium. For this purpose, we highly recommend a product called Seachem Prime.

biological filtration

Goldfish need a filter. Filters not only remove waste from your water, they also provide a vital home for the “good bacteria” that drive the nitrogen cycle.

The effect of pH on the nitrogen cycle

pH is one factor that can interfere with the proper functioning of the nitrogen cycle.

A low pH, below 6, means that the Nitrosomonas bacterium will not be able to process ammonia properly. If the pH gets too low, the nitrogen cycle will stop completely. Similarly, you don’t want your pH to be too high.

A healthy pH in the 7.0 to 8.0 range is just about right.

How to cure ammonia poisoning in goldfish

Like most goldfish problems and diseases, ammonia poisoning is better avoided than treated.

It is much easier to maintain a proper cycle in the tank, not to add too many fish and avoid overfeeding, than to lower ammonia levels and treat goldfish once ammonia has become a problem.

However, ammonia poisoning can be treated.

Step 1: Find out what the problem is

The first step is to determine the cause of the high ammonia levels.

There is no point in trying to treat ammonia poisoning while the underlying problem remains. First you need to eliminate the cause of the high ammonia levels.

For example, if you find that there are too many fish in your tank, you will need a larger tank.

Step 2: Move the Fish to the Quarantine Aquarium

Removing the affected fish to a quarantine tank can be a good move while you are dealing with problems in the main tank.

For example, if you have two goldfish in a 10 gallon tank and you find it too small for them (which it is!), it would be beneficial to buy a larger tank and separate the fish. You can keep one fish in your 10 gallon tank and move the other to a 30 gallon tank. When everything is ready, 30 gallons can become their main home.

However, remember that ammonia can also accumulate in quarantine tanks! Therefore, you will need to test both tanks in order to maintain safe water parameters.

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Step 3: Stop or drastically reduce feedings

Goldfish can live for a long time without food. Therefore, it is safe to stop feeding your goldfish or feed them small amounts while you work on controlling your ammonia levels.

Feeding reductions will mean less rotten food and less fish waste, which means less ammonia.

Step 4: Increase your water changes and test, test, test!

Since the nitrogen cycle does not reduce ammonia levels, you will have to do it manually.

Get a test kit and do a big water change every time your ammonia level gets high.

You’ll want to measure nitrite and nitrate levels, as well as ammonia. When you measure zero ammonia, zero nitrite, and some nitrate, you know your aquarium is cycling.

Step 5: Help Your Fish Breathe

Because ammonia poisoning can permanently affect your fish’s ability to breathe, it’s a good idea to add aeration items to your aquarium.

Air stones and bubblers will keep the water moving, including on the surface, and help more oxygen get into the water.

You can also try to keep the aquarium water cool, as colder water contains more oxygen than warmer water.


Ammonia poisoning can be a very dangerous problem.

The best way to avoid ammonia buildup is to make sure your tank is properly cycled. This means that bacteria convert ammonia to nitrite and then to nitrate, which is removed during a water change.

Check your aquarium water regularly to make sure ammonia levels don’t start to rise without your knowledge.

The proper amount of ammonia in the tank is zero.

If ammonia starts to build up, it could be a sign of a problem with the nitrogen cycle, an overfilled tank, or too much fish food.

Treating a high ammonia tank will require multiple water changes to keep the ammonia under control until the tank is working properly.

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