Why Is My Goldfish Turning Black? [4 Reasons & What to Do]

Why is my goldfish turning black?! If you wake up one day and notice that your goldfish is turning black you might be quite concerned. Especially if you’ve never seen anything like this before. But is it really something to be worried about or is it a normal phenomenon? Goldfish are usually pretty low-maintenance pets, but things like this can happen, and it’s best to be prepared.

There are many different reasons why your goldfish is turning black. Some of them are bad, like ammonia poisoning or black spot disease. However, it can also be harmless and simply due to genetics. The most likely reason why your goldfish is turning black is ammonia poisoning, which should be remedied as soon as possible by removing waste from their tank and changing the water.

In this article, I’m going to go over everything you need to know about your goldfish changing color. I will discuss whether or not this is something to be worried about, what you can do to remedy it, and much more.

Reasons why goldfish turn black

There can be several reasons why your goldfish is turning black. Let’s take a look at each one of the reasons individually. That way, you can best determine which one applies to your goldie.

Ammonia poisoning

goldfish turning black because of ammonia

Let’s start with the most dangerous, and most common reason why your goldfish is turning black: ammonia poisoning. Ammonia is a gas that gets released into the water when their waste, plants, and uneaten food starts decomposing. If you do not clean their cage and change the water often enough the ammonia levels will build up. This build-up of ammonia will actually burn your fish’s scales and make them turn black.

To prevent this from happening, it’s essential that you remove the waste from their tank often enough and change their water.

If it’s already too late to prevent it and your goldfish is already developing black spots due to the ammonia build-up make sure to remove the waste immediately and give them a 60% water change. By doing so, the ammonia levels in the water will drop and your fish will start to heal. However, some of the black spots will turn into black patches and these will not go away; they’re kind of like scars on their scales.

If the ammonia levels are too high in your goldfish’s tank you might notice strange behavior. For instance, a loss of appetite, floating on their sides, and sitting on the bottom of their tank are all signs of there being too much ammonia in the fish tank.

If you do not remove the waste and continue to let the ammonia build up it can result in the death of your fish, so make absolutely sure to do this as soon as you can.

The best cure is prevention. Preventing ammonia build-up in the water is pretty easy; just remove the waste and keep the water fresh. The best way to keep an eye on the ammonia levels is by using a special aquarium ammonia meter like this.

Black spot disease

Black spot disease is something many goldfish owners are concerned about. It’s possible that your goldfish is turning black because of this, but it’s not very likely. The only way this happens is if you have snails in the same tank as your goldfish or if you keep them in an outdoor pond.

You see, black spot disease is not an infection but rather a parasite. The parasites are dark in color and burrow under the scales of the goldfish, which is what causes the visible black spots. If you keep your goldfish in an aquarium inside without any snails then there’s almost no chance of them having these parasites.

On the other hand, if you keep your goldfish in an outdoor pond this is more likely to happen. The reason is that in an outdoor pond bird poop will land in the aquarium. The bird poops can contain the parasite which will then find its way to your fish. On top of that, snails also find their way into the outdoor pond quite frequently and can thereby introduce the parasite.

Once the parasite finds its way to the goldfish it will show several symptoms: you will notice black cysts developing and your fish might start rubbing its body against surfaces due to irritation from the parasites.


It’s also possible that your goldfish is turning black simply because of its genetics. Goldfish are often a mix of species and are therefore not guaranteed to keep their orange coloring. Instead, it happens quite frequently that their scales turn black. This often happens within the first year, but not always. It’s possible that it happens later in their life.

If this is the case, it’s nothing to be worried about and there’s nothing you can do to change it.


It’s also possible that your goldfish has black spots due to bruising. If you recently bought a new fish and notice that he has black spots on him, it might be because the person you bought him from handled the fish improperly and too rough. This can result in bruises that show up several weeks or months later.

There’s nothing you can really do about this, they go away on their own.

Is it normal for goldfish to change color?

It is actually quite normal for goldfish to change color, depending on the cause and what color they change to. In this article, I’ve already discussed the reasons why they turn black, and that this is usually due to ammonia poisoning and is therefore dangerous but they can also turn white, red, or yellow.

If they’re changing color because of their genetics it’s completely normal and nothing to be worried about. However, if they’re changing color due to illness then it’s not normal and you should work to remedy this issue as soon as you can.

How do you get rid of black spots on goldfish?

You might be wondering if the black spots on your goldfish will go away. They can, but it depends on the reason why they have them.

If your goldfish has black spots because of their genetics there is no way to remove the black spots. It’s simply part of who they are and is nothing to be worried about.

On the other hand, if it’s black spot disease, make sure to remove all snails from their tank or pond.

If it’s because of ammonia (the most common reason) make sure to remove all waste from their tank and give them a water change. They might have black patches that will stay with them for the rest of their life even if you fix the ammonia situation.

If it’s because of bruising, there’s nothing to do but wait. Over time your goldfish will heal and the black spots will disappear.

Why is only one of my goldfish turning black?

If you have multiple goldfish in the same tank and only one of them is turning black then it’s pretty safe to rule out ammonia poisoning.

After all, they all swim in the same water so the ammonia would affect all of them. Nevertheless, it can never hurt to test the ammonia levels in the water through the use of a meter if you want to be sure.

If only one of your goldfish is turning black then it’s most likely due to either bruising or genetics and therefore nothing to be worried about.

Final words

Goldfish can turn black for a variety of reasons. Most commonly, one of these 4 things is behind your fish changing color:

  1. Ammonia poisoning
  2. Black spot disease
  3. Genetics
  4. Bruising

Some of these, like genetics and bruising, is not a huge deal, while the others are very bad and dangerous. If you notice that your goldfish is turning black it’s always important to check for and rule out ammonia poisoning and black spot disease because these can end up being lethal to your fish.

ThePetFaq Team