Why Is My Fish Turning Black? 4 Main Causes & Treatments 2022

People keep ornamental fish as pets primarily because of their vibrant and alluring color diversity.

Nevertheless, these creatures are not perhaps in good health if these colors transform, particularly when they turn black.

As a newbie aquarist, you may wonder: Why is my fish turning black? There are various reasons behind it.

Let’s scroll down this article to learn more about the potential causes and ways to prevent this problem! Read on!

Why Is My Fish Turning Black?

Black spots can appear on your fish for various causes, such as ammonia changes, genetics, stressful tank environments, disease, and more.

Keep reading to learn the potential causes if your pets have darker patches.


This explanation is particularly relevant to betta and goldfish. These species have undergone mixed breeding to get unique color patterns.

Numerous goldfish and bettas come in mixed-color varieties. The color changes will be inconsistent if the crossbreeding procedure does not go smoothly.

It indicates that as they age, this species will develop new pigments, which may occasionally be black instead of yellow, orange, or yellow.

Some creatures may permanently change their coloring to black, while others will briefly turn dark color before returning to their previous patterns.

Therefore, when it occurs, you should not be concerned; understand that genetics is to blame.

black fish


Ammonia Burn

The most damaging and frequent reason for the blackening of a fish scale and fin is ammonia burn.

The tank water’s disorganized state is the primary cause of ammonia burn and poisoning.

Most fish keepers will often feed their pets as much as possible and be happy with this feeding schedule.

However, these creatures don’t need frequent feeding. Thus, bad things occur when you overfeed them.

Overfed creatures excrete a significant amount of waste into the water in the tank. It gradually sinks into the water and builds up there.

Moreover, a large percentage of the meal portion remains uneaten if you put excessive snacks in the aquarium. The bottom of the tank becomes clogged with these residues.

Ammonia gas is released into the tank’s water when decaying waste combines with chemical compounds in the atmosphere.

Ammonia steadily builds up a condensate layer in your tank because it can’t escape the water.

Burning your fish’s fins and scales will probably occur in a tank with high ammonia levels.

These burns may get so bad that ammonia toxicity may cause the entire animal to turn dark color progressively.


Aquatic creatures in stressful tank conditions may develop black patches on their bodies.

Your pets may get stressed and become dark because of bullying from other species, being tossed over by the filtration circulation, or unfavorable water temperatures.

Black patches that develop on your pets may be bruises caused by collisions with other species in the aquarium.

Your pets might get hurt while floating and bumping against some decorations with sharp edges or rough textures.


Do fish turn black when sick? The answer is yes! The disease is among the common reasons causing black spots on your pets.

Aquatic creatures kept in captivity may contract the parasitic Black Spot Illness from the other species that share their aquarium, like snails.

According to the Indiana Department of Natural Resources, cysts develop whenever the parasite enters the fish’s epidermis.

These creatures develop black spots on their body due to the cysts and nearby scales seeming to be darker.

Black areas on your pet’s body are frequently more noticeable than on their fins, where the illness can also manifest.

This sickness does not kill these aquatic creatures as quickly as ammonia poisoning does.

How do you treat black spots on fish? Keep reading to find the solutions.

black spot on fish


How To Stop Fish From Turning Black?

When you notice your pet turning a dark color, you will want to take action right away to stop the fish’s agonizing moments.

What do you do when your goldfish turns black? Below are some of the most effective ways to apply:

Change The Tank Water

When you notice your pets becoming dark, check the water’s conditions immediately.

Since ammonia is the primary cause of fish becoming darker, it is preferable to start with this test. You’ll need to purchase ammonia test strips or liquid.

The strips may be because you must drip one into the tank water and watch the readout.

The liquid analysis, nevertheless, yields more detailed findings. Dechlorinate the water appropriately before changing it to prevent arising issues.


Change the tank water

Add Carbon To The Filtration System

Check to see if your carbon filtration system is active in any filters already installed in your tank.

The likelihood of the carbon being out-of-date is high. If that’s the case, it’s a good idea to add new carbon to the filter and wait some days to get the results.

The carbon filtration system should ideally restrict ammonia build-up before gradually and adequately removing it from your aquarium.

If you want to learn more about this filter, you can watch this video:


Use Water Prime

Water prime or conditioners are helpful to safely convert the harmful ammonia fuel into a chemical and aid fish recovery.

Nevertheless, only water prime can’t wholly treat the condition that causes the creature’s epidermis to darken.

Therefore, you must earnestly take action to aid the aquatic creatures in becoming better.

Feed Sufficient Food

If you notice that your pets are becoming black, stop overfeeding them right away.

These species won’t perish if you give them less food or stop giving them for a day or two.

Because these aquatic creatures are resilient, they can survive a few days without eating.

Additionally, when you cut back on feed intake, ammonia will gradually leave your aquarium.

fish eating food

Feed sufficient food

The Bottom Line

This article has eventually solved your question: Why is my fish turning black? Several causes explain this issue.

These creatures turning black may be due to genetics, ammonia burns, stress, or disease. Luckily, you can apply many ways to save your pets!

Hopefully, this post will be helpful for you. Thanks for taking the time to follow it!