5 Causes Of Black Spots On Goldfish (& How To Treat Them)

Last Updated on 2022-11-15

If you’ve noticed black spots on your goldfish, then it could be a sign that something is wrong. In this article, not only will you find out if black spots are normal, but you’ll also learn why your goldfish has black spots, how to treat black spots, whether they’ll go away on their own, and much much more!

So keep reading to find out everything you need to know!

Are Black Spots On A Goldfish Normal?

If the black spots on your goldfish aren’t genetic and haven’t always been there, then the chances are that they’re not normal, and there’s a problem. So if you notice they’ve popped up out of nowhere, it’s time to start diagnosing.

Why Does Your Goldfish Have Black Spots?

If you notice that your goldfish has black spots, then it could be for any of the following reasons:

Ammonia Levels Are Too High

One reason that black spots might be occurring is that the ammonia levels in the tank are too high. When the ammonia is too high, it will begin to cause a chemical burn in your goldfish that causes black spots to occur.

As well as black spots, you may also notice that your goldfish’s gills are turning black, they’re swimming erratically, they’re struggling to breathe, they’re gasping near the top of the tank, and they aren’t moving around as much anymore.

So if you notice the following, you should test the water immediately to make sure the ammonia hasn’t spiked.


Another reason your goldfish might be turning black is because of diseases. One disease that goldfish are susceptible to is Black Spot Disease, which is a parasitic disease that occurs on your fish’s body.

While black spot disease is more common in goldfish living in ponds, it can also happen to goldfish kept in tanks as well.

Recovering From An Injury

Sometimes, it may simply be the case that your goldfish is recovering from injuries it may have sustained earlier. Just like we scab and scar when we’re injured, it’s not uncommon for goldfish injuries to turn black, which could result in the black spots you see.


Sometimes the reason that your goldfish is starting to get black spots is simply because of genetics. Oftentimes, these black spots will be there from the beginning; however, it’s entirely possible for the black spots to come and even go as your goldfish ages.

Not Enough Light

Sometimes black spots can also occur when your goldfish isn’t getting enough light. This is because they’ll begin to produce more melanin to camouflage themselves better from predators.

Gold fish or goldfish floating swimming underwater in fresh aquarium tank with green plant. marine life.

How To Treat Black Spots On A Goldfish

If you notice black spots on your goldfish, then there’s a good chance they’ll need to be treated. If you think treatment is necessary, then here’s what you’ll need to do!

Ammonia Poisoning

Ammonia poisoning is the most threatening problem a goldfish can face, so if you think that’s the problem, then you’ll need to act immediately.

Before anything, you should perform a 15-30% water change. Doing so will remove a large amount of water from your tank, as well as diluting the remaining amount, lowering the ammonia dramatically.

As well as performing a water change, you should also use an ammonia neutralizer like API Ammo Lock. Ammonia neutralizers are great as they render the ammonia harmless but still leave it in the tank for the beneficial bacteria to consume (these bacteria will help ensure another spike doesn’t happen again).

Once you’ve got the ammonia levels down to 0ppm, you’ll need to make sure you’re not overfeeding, you’re cleaning your tank regularly, and you’re using a filter as well as performing water changes to ensure the water stays that way.

If you’re keeping a goldfish in a new tank, then you should also be testing the water frequently to ensure the parameters are good.

Treat Black Spot Disease

If you think that your goldfish is suffering from black spot disease instead, then you’ll have to begin treating that as soon as possible. Fortunately, treatment is incredibly simple. 

First of all, move your goldfish to quarantine so the other fish you’re keeping don’t get sick. Next, you should then mix some aquarium salt with the tank water before adding the mixture into the tank you’re keeping your goldfish in. (As a rule of thumb, you should add ½ teaspoon of aquarium salt for every gallon of water.

Then it’s just going to take time for your goldfish to get back to normal. The good news is that while Black Spot Disease may not be the most pleasing to the eye, it’s extremely unlikely to cause serious harm to your goldfish!

Recovering From Injuries

If your goldfish is recovering from injuries, there’s not much more you’ll need to do to ensure that they’ll get better, as they’re probably doing well on their own.

However, one massive recommendation I would give is to add API Stress Coat to your tank. API Stress Coat is great because it contains aloe vera, which helps reduce stress while also improving the quality of the water as well!

And on top of this, you should also make sure you’re keeping the tank clean by performing frequent water changes, vacuuming the gravel, and removing any uneaten food as well as fish and plant waste.


If your fish is starting to get black spots due to genetics, there isn’t a lot you can do. You’ll just have to accept that this is your goldfish’s new look.

How To Prevent Black Spots On Your Goldfish?

If you want to reduce the chance of black spots occurring on your goldfish, then there are a few things you can do. While this won’t work for black spots which are caused by genetics, it can help prevent black spots due to other causes!

Perform Frequent Water Changes

First of all, make sure you’re performing frequent water changes. You should be removing 10-20% of your goldfish’s water every 1-2 weeks to ensure it’s staying clean.

Clean The Tank

Cleaning the tank frequently is also paramount in keeping your goldfish healthy and avoiding black spots as well. Removing fish waste, decaying plant waste, and old fish food will keep the ammonia levels low and prevent ammonia poisoning, as well as reducing your goldfish’s stress overall too!

Make Sure The Tank Is Big Enough

You should also make sure your goldfish are in a big enough tank. As a rule of thumb, one goldfish needs a 20-gallon tank, with each extra goldfish needing an extra 10 gallons.

Goldfish are extremely messy fish, so a big tank is essential to ensure a waste buildup doesn’t occur.

Use A Filter

You should also make sure you’re keeping your goldfish in a tank with a filter as well. Filters are essential for removing all the waste from your tank and keeping the water as clean as possible.

Quarantine Sick Fish

If you know your fish is sick, then you should quarantine them as soon as possible. Even if the sickness isn’t causing black spots, it could increase the chance of your other fish suffering from disease, which will weaken their immune system, opening them up to more black spots occurring.

Ensure They’re Getting Enough Light

You should also ensure that your goldfish are getting enough light a day as well. Generally speaking, 12-16 hours of light a day and anywhere between 8-12 hours of darkness is going to be perfect for your goldfish.

A simple way to remember this is to just turn the tank light on when you wake up and turn it back off when you fall asleep.

What Other Signs Should You Watch Out For On Goldfish?

As well as black spots on your goldfish, you should also be aware of the following problems as well!

White Spots

One of the most common sights you’ll notice on your goldfish is white spots. If you notice white spots on your goldfish, then the chances are they’re suffering from ich, which is a parasitic disease.

Pale Color

If you’ve noticed that your goldfish appears a lot paler than they used to, then it’s a sign that something is wrong. Perhaps, they’re getting enough light, or more likely, they are stressed and sick.

White Gills

If you notice that your goldfish’s gills have turned white, then there’s a strong possibility that they’re suffering from a parasitic infection or flukes of some kind.

Gold Spots

If you notice gold-like spots or a general gold dusting over your goldfish, then they could be suffering with velvet, which should be treated as possible to ensure the survival of your goldfish.

Red Spots

If you notice red spots on your goldfish, then they may be suffering from a parasite such as anchor worms and lice, and you should begin immediate treatment to keep them healthy.


Now you know why black spots are occurring on your fish, here are some more frequently asked questions that people have!

How Long Do Black Spots Take To Heal On Goldfish?

The amount of time black spots take to heal on goldfish varies wildly. The minimum amount of time it will take is two weeks; however, there is no upward amount of time. Especially if the black spots are simply caused by genetics.

Will Black Spots On Your Goldfish Go Away On Their Own?

The good news is unless it’s genetic, the black spots on your goldfish should go away once you’ve improved the quality of the tank and treated them if they’re sick!

Does Black Spot Disease Kill Fish?

Fortunately, even though black spot disease is a parasitic infection, it’s extremely unlikely to be fatal to your fish. If you have juvenile or senior fish, though, they will be a lot more likely to succumb to the illness.

Can Fish Develop Black Spots When Stressed?

Stress alone isn’t likely to cause black spots on goldfish. However, if you notice black spots on your goldfish and it isn’t genetic, then the chances are there is something wrong with them, and they’re also stressed.

Why Does Your Goldfish Have Black Spots On Its Fins, Tail, Or Head?

If your goldfish is getting black spots on its fins, tails, or head, then it could be due to not getting enough light, ammonia poisoning, genetics, black spot disease, or because it’s recovering from an injury.

Why Are There Black Spots On Your Goldfish’s Gills?

If you notice black spots on your goldfish’s gills, then the chances are a lot of damage has been done to them. Most likely due to ammonia poisoning. If you see this, you should immediately transport them to a quarantine tank where the ammonia is at 0ppm.

Why Have The Black Spots On Your Goldfish Started To Disappear?

If you notice that the black spots are slowly starting to disappear, then the chances are they were healing from an injury, and now they’re fully healed.

Is Black Spot Disease A Hazard For Humans?

There is no chance of black spot disease being transferred to humans, so if you’ve come into contact with it, you don’t need to worry at all!

How Do You Improve The Color Of Your Goldfish?

If you think that your goldfish has lost vibrancy, the best thing you can do is make sure the tank water is clean for them, give them enough light, and provide them with the most nutritious food possible.

Remember, goldfish are omnivores, so they should be getting a mix of meat and plants.


As you can see, as long as the black spots on your goldfish aren’t being caused by ammonia poisoning, the chances are you have nothing to worry about. 

With that being said, you should still do everything in your power to make sure you’re treating your goldfish well and keeping the tank clean for them.

If you liked this article, make sure you check out the rest of the website. Otherwise, have a great day!

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