Why Does A Goldfish Turn Black?- Causes and Measures

Why does a goldfish turn black
Why does a goldfish turn black? Some of the Goldfish enthusiasts or owners must be wondering.
Generally, goldfish are considered low maintenance pets. But, when it starts to turn black, the question that erupts in your mind is, why does a goldfish turn black? What can I do about it? How can I stop my goldfish from turning black?
There are several reasons why a goldfish turn black. Some of the causes are harmless natural reasons and whereas others may be grave.
Let us look at the various causes and how to determine and diagnose the reason why the goldfish is turning black; the measures to fix the issues that are causing them to turn black.

The causes of why does a goldfish turn black:

Goldfish turning black is not a usual occurrence amongst all types of goldfish. Most often, the complaints are them turning white and die. It is not common for them to go from silver-grey or orange or yellow to black. Generally, a black goldfish turns to orange-gold or yellow-gold because black is an unstable color in goldfish.

When you see a goldfish turning black must be disheartening, and immediately we tend to connect it to some disease; although it may be the cause, there are other reasons why a goldfish turn black.

The major causes of why a goldfish turn black are:

Burning from Ammonia:

ammonia spike goldfish turning black

Ammonia is by far the most common reason why does a goldfish turn black. It is a toxic chemical produced within the tank environment from the poop of your fish, left-overs, decaying matters, etc.

Stressed fish:

A fish under stress produce tons of ammonia. Newly transported fish would have tremendous stress levels. Even with the filtration running, a stressed goldfish will generate tons of ammonia in the tank. Frequent water change can minimize this situation.

Over-feeding the goldfish:

Over-feeding the goldfish is another reason why ammonia can build up in the tank. Over-feeding results in excess waste production by the fish; the bio-media in the filtration system may not be able to process the waste.

Newly established tank:

Ammonia build-up is also common in a new tank where the bio-media in the filtration has not yet established the biological enzymes necessary to digest the ammonia and the nitrates.


Another reason why does goldfish turn black is that they have black spot disease. It is a potentially worrying reason as black spot disease is a rare occurrence in goldfish, particularly in an aquarium tank.
It is a deadly disease and can kill your goldfish. Hence, it is essential to rule out this cause.
Blackspot disease is also known as fluke disease. It is a freshwater disease caused by larvae of the genus Neascus, carried by water snails. The larvae of these parasites dig deep into the skin of the goldfish.
Look out for the snails in the tank; if you see your tank is snail-infested, the first order of the job is to clear snails off the tank. Check your water parameters as the presence of snails denotes the presence of ammonia in the water.
The Black Spot disease is usual with the fish that are in the outdoor ponds. The snail infestation and the bird droppings transmit the parasites in the water.

Genetics and Breeding:

A goldfish turning black due to genetics or breeding is a harmless and innocent cause. Goldfish turning black is a rare phenomenon, and yet it is still possible.
Goldfish just doesn’t come only in gold color; they come in varieties of colors and shapes, such as orange, red, reddish-orange, yellow, yellowish-orange, gray, silver, white, and even black.
To understand this, you should know that goldfish is a freshwater species from the family of Cyprinidae of the order of Cypriniformes. It is a relatively small member of the carp family, which is native to Eastern Asia.
In the beginning, various carps were reared for food like most of the fishes by ancient Chinese. Goldfish was one of the common fishes eaten by the ancient Chinese. In the wild, they were a dull grey or silver grey, or olive green color.
The first orange-red goldfish was produced by natural mutation during the period of the Jin Dynasty (AD 265–420). By the 7th-8th century, goldfish became part of the ornamental ponds and water gardens.
During the 17th century, goldfish entered Europe through Portugal, and it first came to North America in the mid-1950s. Before we knew it became the most popular fish in the American aquarium trade.
Today, the goldfish you see in your tank or the pond is the result of centuries of cross breedings. So, the specimen that you have may not have been bred for pure gold color by the breeders. Often, they come in mixed colors such as gold with black and white, gold with orange and black colors, etc. and these colors can change over time.
During the first couple of years of their lives, goldfish keep developing and will have a shift in colors and also might form a new variety of color spots.
A goldfish turning black as a result of genetics is cause for no worries. It will not have any health effects on your goldfish. The fish will continue to live to its optimal capacity with the right care and clean water.
The only thing you have come into terms with is that your goldfish is not gold, it is black.

Blending into the Environment:

Another innocent and harmless cause could be your fish is trying to imitate its habitat. If you have recently changed the backdrop, decors, foliage, etc. of the tank might induce melanin production in the fish to blend into their surroundings.
In nature, it is called a protective measure. Color changes happen instinctively to protect themselves from predators by blending themselves into the environment.
In this case, you need not worry about the health of your goldfish.

How to Diagnose Why Does A Goldfish Turn Black?

Ammonia Burns:

If you see irregular and patchy spots in the fish body, you would want to test the water for ammonia, nitrate, chlorine, chloramine, etc.

You can use the test kit, which is widely available in most pet stores as well as online. You can also use strips, which pretty easy to use though liquid testing is more accurate.

Remember, black spots, patches meaning the fish is healing from the burn. All it needs is a spike of ammonia to burn the fish. In that case, you would want to run a complete water test and do a thorough check for snails in the tank. 

Black Spot Disease:

black spot disease


As mentioned earlier in the article, Black Spot Diseases comes from larvae of the genus Neascus, which is carried by snails.
If you have snails in your aquarium as a part of the cleaning crew, move them to a separate tank and watch whether your goldfish makes any progress.
Even you have not added the snail yourself, still do a thorough snail search in the tank as it is quite possible for snail eggs or baby snails to have taken a ride with some other fish or decors you have introduced to the habitat.

Natural Causes:

If you see, the black spots are almost symmetrical and closer to its extremities, then it’s most probably a natural occurrence. Genetics are in play here.

Check its environment backdrop; if the environment is dark with plenty of dark matter around, then the fish is trying to imitate its habitat. 

Just replace the dark decors with more bright color decors, and change the color of the backdrop. Your fish will take the queue and lose its black spots. 

If your goldfish doesn’t lose its black spots and continue to turning black, then check its lineage if you have access.

If your goldfish continue to turn black and still eating healthy and looking healthy, then it is very likely, it is a natural cause.

How to fix the Ammonia level in the water?

If you see white or black patches on your fish, then test the water for ammonia. The ammonia level in the water should be 0 parts per million.

Test and do the water change:

The presence of ammonia indicates the absence of bio-media/beneficial enzymes in the tank environment. If the water sample reads any trace of ammonia, stop feeding your fish immediately, and increase the filtration cycle as ammonia is the first by-product in the nitrogen cycle. If possible, move the fishes to another tank and do the water change.

In case the reading shows the ammonia level 0, do a test for Calcium Carbonate in the water. 

If KH is over the recommended limit, add vinegar by premixing 0.5 – 1 tsp per gallon of water. Start with 0.5 tsp of vinegar/gallon and wait for an hour or so, test for KH, then again dilute some more vinegar till you bring it down in the range of 4 to 8 KH.

Limit the Food:

Reduce feeding your goldfish, or completely stop feeding for a day or two. Generally, the goldfish are over-fed, and they are messy. You would want to remove uneaten food and clean up solid wastes from the tank to reduce the load on the bio-moss of the filter. If not, consider installing a bigger filtration system for the tank so that it provides more bio-moss/enzymes to digest the waste.

Add Carbon:

Add carbon to your filtration system; carbon locks all the toxins in the water, including ammonia. If you are already using one, then replace it with a new one. Change the carbon for a few days till the water stabilizes. You can also a piece of charcoal in the tank and replace it with a new one frequently.

Add Prime to the Aquarium Tank:

The Prime is a conditioner that removes Chlorine and Chloramine from the water, allowing the bio-filter to digest ammonia and nitrite completely. 

How to treat Black Spot Disease:

How to treat black spot disease is simple and straightforward. First of all, clear all the snails off the aquarium tank (this could be a problem in outdoor ponds) and closely monitor your tank for any sign of snails.

You would want to check all the decors, plants, and hiding places in the tank for the snails. Once you are through with clearing off the snails from the tank, you would want to do the ammonia treatment.

If you see the black spots in your goldfish that are in the ponds, then move them to an indoor tank if you have one or to a tub or a bucket of clean water. Do the water change every day to see any changes with the blackspot. Note: Water should be free from Chlorine and Chloramine.

If you see that the black spots are fading, you would want to clean up your pond. You can also tie up a net above the pond, preventing bird droppings.

Do goldfish turn black when sad:

Some ask that “do goldfish turn black when sad?” Well! It is also one of the causes why does a goldfish turn black. 

Julian Pitman, a professor at the Department of Biological and Environmental Sciences at Troy University in Alabama, says that fish are not only suffering from depression, but you can also diagnose the symptom. The fish that are depressed or sad will not have the interest to explore or eat or both.

Goldfish, like any other pets like cats, dogs, react to human emotions and health conditions. It is not just us who improve our health, watching the goldfish tank but, the fish imitate us as other pets do.

Can a goldfish go back to its original color?

Well! that depends on the cause for which they turned black. 

If the cause was Ammonia poisoning, the concern is whether the fish will make it. It all depends on how fast you spot the problem and do the corrective measures.

Once they make it, and you provide them with an optimal living condition, then yes, they can revert to their original color. 

If the reason for color changing is due to its environment, then you know what to do for them to come back to their original color.

If it was the play of its genetics, then the fish will remain black for the rest of the life, but healthy. Nothing to worry about!

How to prevent a goldfish from turning black?

Now, we know the causes of why does a goldfish turn black, we can take precautions and prevent it from happening again:

1. Run periodical water test:

Run a regular test for water parameters such as ammonia, nitrate, nitrite, chlorine, chloramine, pH, temperature, calcium carbonate, etc. I would suggest a bi-weekly test, and every time you add an element such as a fish or a decor or a plant, run the test religiously. Or you see any abnormal behavior or a visually the water looks dirty or murky.

2. Avoid Snails:

There is no doubt Snails are a great cleaning crew member, but you should avoid housing them with the goldfish. Instead of snails, you can opt for shrimps such as Amano shrimp, Bamboo Shrimp, Cherry Shrimp, etc. as the shrimps are the much better cleaning crew, especially Amano Shrimp.

3. Avoid Overfeeding:

As a rule, feed them only as much as they can eat in 3 to 5 minutes. Remove the leftovers if you see them after an hour or so. 

4. Clean the aquarium regularly:

Regular cleaning of the aquarium is paramount to have healthy goldfish apart from running the filtration and cleaning crew. 

5. Water Change:

Complete periodic water is necessary for a thriving goldfish.

6. Bright color backdrop and decors:

Try and avoid dark decors and substrates for goldfish. Go for a bright color backdrop and decorations.

Share with us here below, if you have or had any experience of keeping goldfish.

3 thoughts on “Why Does A Goldfish Turn Black?- Causes and Measures

  1. Athur says:

    My bubble eye goldfish is recently turning black and I am starting to worry. I had a similar case before and my goldfish’s fins, scales and tail also gradually turned black. It eventually died after a few weeks. This time I desperately want to avoid the similar thing happen to my bubble eye goldfish so I changed the water. However, its tail also seem to be turning black.

    • Athur says:

      goldfish turns black because of non-physiological reasons, which can be a sign of danger to your fish. When you see a goldfish starts to develop black spots located on the fins or the body, it is probably because the water contains a high ammonia level.

      • SNBrehamet says:

        Yes, ammonia is one of the main causes why your fish can turn black. If you have identified the problem, the first is to change the water; also, look for any decaying leftover food or leaves. Most times the problem is simple, over feeding; you would always want to remember the 3 minutes rule, feed only as much as your fish can eat in 3 minutes. Goldfish never stop eating on their own accord, we will have to monitor the quantity of their food intake, just need to apply the 3 minutes rule.
        I hope you have saved your Bubble eye this time; they are one of the delicate Goldfish types. Take care!

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