Why Is My Goldfish Turning Black? What Should I Do?

Why Is your goldfish turning black? Are you looking for the reason and solution?

It is important to keep in mind that in normal cases, goldfish do not turn black. 

Unless there are no health issues, the goldfish don’t turn black. So when you notice that your goldfish is changing color, then it’s really a matter of concern.

It is usually a sign that the aquarium water parameters are or have been damaged in the past and need to be fixed. Or, your fish is internally suffering for some reason.

Understanding how to resolve and prevent goldfish color-changing problems and get a solution can make your goldfish long, live, and healthy.

However, in some cases, gold can change its color to black, which is not a life-threatening problem for your goldfish. It is completely natural.

But how do you know if it is a health issue or a normal situation?

Why is My Goldfish Turning Black?

Several factors could be contributing to goldfish turning black, including genetics, disease or parasites, and water quality. Monitoring your goldfish’s behavior and body for lethargy, parasites, and discolorations can help you get the source of why your goldfish is turning black.

Environmental factors such as too small a tank or infrequent water changes can quickly cause discolorations in goldfish. 

If you suspect your goldfish has been harmed in some way, this could also have contributed to the goldfish turning black. 

Gauge your goldfish’s current environmental situation and think of any recent changes that have been made or inherent dangers in your aquarium (such as sharp edges).

Naturally Turning black

Goldfish have different cells in their skin. One of them is called melanin that produces black pigment and turns the goldfish tail black naturally.

It is normal for goldfish to change their color due to its location and surroundings. Especially the light-matter. If a goldfish has a darkish area in the aquarium or there are very few lights, the goldfish may have a blackish color. On the other hand, when it is in extreme light, it can be brighter to look.


The goldfish is naturally undergoing color changes due to its genetics, which is usually normal. 

If your goldfish is from a bad home or was rescued under questionable conditions, they could have lost their color due to stress and are not regaining it with their strength.

 Even if you got your goldfish from a fair or carnival, these conditions are stressful and could result in loss of color until a proper environment is restored for them. 

If you notice your goldfish losing color and turns black, this is cause for concern as it usually indicates excessive stress in the goldfish. 

This could be due to a lack of proper husbandries, such as too little water changes.

Black Spot Disease

Though black spot disease is less common to adult fish, it can happen when you keep snails in the same tank. In those cases, a black spot comes from a parasite, and then the parasite lays eggs. Afterward, the egg turns into larvae that get shelter into the fish’s skin.

Then the fish will start to protect himself by creating hard cysts that look very dark and black.

If the dark spot seems like this, the fish will flick and rub against the surface. Because it is very irritating to fish.

With this comes the release of parasites, and is more common in outdoor pond environments.

Water Parameter Spikes

It is the most likely reason due to unstable or extremely unfavorable water parameters. 

Water parameters concern pH, high range pH, ammonia, nitrites, and nitrates. These, including temperature, should all be within certain ranges in order for your goldfish to thrive. 

When these parameters damage your goldfish physically, the goldfish’s immune system compensates while it heals by turning that area black. 

Out of all of these, ammonia burns are the most likely culprit for black smudge spots in goldfish.

Ammonia Poison

Ammonia poison is one of the most common causes of goldfish turning black. When you treat your fish with more food than is required, the ammonia can increase in the aquarium and then cause goldfish color change.

However, this ultimately makes your fish die. So check the aquarium water parameters often to make sure there is nothing happening like this. 


If the fish tank has extreme waste, then ammonia can grow up early and make your fish burn. So, it is important to make sure there is no extreme waste that causes harm to your fish. When you notice that there is more waste and increasing ammonia, perform a 60% water changes to instantly reduce the waste and ammonia.


Overfeeding is not directly affecting your fish to discoloration. First, it creates waste, and then waste creates problems. When your tank has lots of waste, the filter doesn’t work efficiently and can’t purify the water. In that time, ammonia spikes and creates discoloration of goldfish

What is black smudge?

The black smudge is a kind of black spot that is a very common symptom in goldfish. In general, It is an indicator of goldfish disease or illness. Many goldfish show their symptoms by developing the black spot across the whole body, fins, and tail.

If you notice that your goldfish has a black spot on fins, body, or tails, most probably, it is the black smudge attack on goldfish, and there needs to taking action as soon as possible. It can be a serious issue for your goldfish if there taking no action.

What causes black smudge?

There are many reasons for causing black smudge on goldfish. One of them is the development of parasites. In a fish tank, there are certain tankmates such as snail. The snail brings the parasites into the aquarium and causes the goldfish to black smudge and infect the other inhabitants.

What Causes Ammonia Burns?

ammonia burns

Ammonia is a natural chemical byproduct of processes such as they breathe, eat and excrete. 

While it is naturally occurring, excessive amounts of ammonia have the potential to have lasting and permanent health effects on your goldfish, and it is best if it is avoided.

 When ammonia builds up to a toxic level, it “burns” the goldfish’s eyes, fins, gills, and skin. 

When setting up a new tank, it is important to get a proper cycle (which can often take up to a month to achieve) going so that you do not cause “new tank syndrome”

Because the water is not cycled correctly, ammonia accumulates faster to toxic levels. 

Additionally, the water in the bag from the pet store may have accumulated excessive amounts of ammonia and should not be added to the existing cycle.

 If your goldfish is in a tank or bowl without a filter, ammonia will undoubtedly be a problem without major and frequent water changes, which can be stressful to goldfish. 

The smaller the enclosure, the more likely ammonia is to build up to a deadly level and damage your goldfish’s health. 

When this happens, goldfish do not initially give off any physical signs other than being lethargic. 

When goldfish begin to heal from ammonia burns, their scales turn black as a response to healing.

My Goldfish Is Turning Black What Should I Do?

Why Is My Goldfish Turning Black? What Should I Do? 1
solution for goldfish turning black

Frequent Water Changes

If you are here before getting a goldfish, even better! You have the chance to learn about goldfish husbandry in advance and understand their needs in captivity. 

Goldfish, especially large breeds, need large aquariums or ponds. This is because goldfish have a large bioload, meaning they are messier than your typical fish so they need more cleaning up after.

 When feeding your goldfish, start off with the smallest amount possible and wait until they finish that batch before giving a little more. This can help prevent overfeeding and therefore avoid ammonia spikes. 

Uneaten food can get stuck under decorations and eventually decay, which can cause water parameters to go off of the charts. 

Weekly water changes that include taking out or moving decorations is recommended to loosen any hidden debris.

A Larger Aquarium or Filter.

If your goldfish is in a bowl or tank that is less than twenty gallons, it may be time to upgrade their enclosure for their sake.

Small bowls often cannot have filters, or the current is too strong in small tanks. 

By upgrading their enclosure, you add more water and therefore lessen the number of times you have to do water changes. 

This will also give your goldfish more room to move around and likely make them happier and healthier.

 The Penn Plaxx Cascade 1500 is a good option for those with a lot of goldfish as it handles up to 200 gallons.

Test your Water.

Stress, sick, or agitated fish will give off more ammonia than usual, so it is important to pay attention to any irregular behaviors. 

Giving your goldfish more hides, driftwoods, plants, and less time with lights might help with stress levels. 

A quick and sure way to get to the root of your goldfish’s problem is to test the water parameters,

 which may be the most important part of maintaining your goldfish’s health.

 Water parameter kits come in liquid and strip form, with the liquid being more accurate and the strip being more convenient. 

These regular tests will let you know what parameters (pH, nitrites, nitrates, temperature, etc.) your water quality is actually at, 

and then you can work to tailor them to your goldfish through husbandry changes.

No Snails

Even though black spot disease is rare, it is not recommended to get snails to cohabitate with goldfish. 

This is because snails can transmit other diseases, not only black spot disease, and also reproduce at a massive rate when fully mature. 

In the case of pond snails, the most common and prolific type of snails, they can multiply at alarming rates and soon infest your tank.

 If you really want to get a snail, it is recommended to get a quarantine tank in which they live for one to three months.

 If they show no signs of underlying health conditions, it can be safe to add them in with your goldfish while taking all necessary precautions.

Will My Goldfish Ever Turn Back to its Normal Color?

Why Is My Goldfish Turning Black? What Should I Do? 2
Will My Goldfish Ever Turn Back to its Normal Color?

The good news is that proper aquarium husbandry goldfish can turn back to their normal color and recover from ammonia burns! 

You first have to identify the source of the problem as outlined above and then correct your husbandry as you see fit.

 Another option is to consult your local fish store, which may be able to help you in regards to getting a proper cycle in your aquarium.

 If you are seriously concerned for the health and safety of your fish and have no access to a water parameter kit, 

Amazon offers a free service in which they test your water parameters for free if you bring a sample to a location near you.

What does it mean when goldfish turn black?

What does it mean when goldfish turn black? It means your aquarium has excessive ammonia poison that goldfish can not tolerate. If the ammonia level is so high in the aquarium, goldfish get burned on their scales and skin and turn black.

What happens when a goldfish turns black

Many factors can happen when a goldfish turns black such as blending into its environment, genetics, ammonia poisoning, black spot disease, overfeeding issues, stress, or illness. There are several reasons for goldfish turning black. Some of them are critical regarding your fish health.

Goldfish turning black on fins and body

When goldfish start to turn black, it first begins from fins, and over time, it spreads to the entire body. It looks like a small black spot that looks burnt.

Goldfish tail turning black

All fish have different cells in their skin. These cells can produce a pigment called melanin in the fish’s whole body area, which can cause the goldfish tail to turn black. It can also cause scales to turn black.

Leave a Comment