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Why Do Discus Fish Turn Black?

Did you walk by your aquarium and notice that your discus fish have turned black? Or, did you just buy a new discus fish only to have it turn black shortly after?

Believe me, I know how confusing and frustrating this can be. After all, you thought you were doing everything right!

The good news is that there are a few reasons why your discus fish might turn black and, in most cases, it isn’t anything to worry about.

In this article, I’ll discuss the most common reasons why discus fish turn black and what you can do about it.

What Are the Symptoms of a Discus Fish Turning Black?

Discus fish can turn black for two reasons: either the formation of black markings on their body or a discolored transformation to an eventual loss of brightness.

The first kind of black spot is not an issue, since this is usually typical. However, the second form implies that something is wrong, and it can be accompanied by additional symptoms including:

  • Black spots peppered the body
  • Heavy breathing
  • Glass surfing (move up and down the tank)
  • Hiding in the corners or planted areas
  • Leaning to the side
  • Loss of appetite
  • Lethargy
  • Clamped fins
  • Slime coating
  • Excessive mucus
  • Scratching against objects
  • Erratic swimming patterns
  • Twitching
  • Fin rot
  • White spots
  • Cloudy water from excess mucus

Why Is My Discus Fish Turning Black?

Dark Background

I know it seems like a no-brainer, but it’s possible that your discus fish are simply trying to blend in with their background.

Discus can blend in with a dark background, making them appear black. If the discus is new to the tank, it may also be trying to camouflage itself against predators.

However, they will not turn entirely black. They will only have small black spots on their body which is called “black peppering” (diplopstomiasis or fluke disease) and usually isn’t indicative of an illness.

Bad Water Parameters

When we first get into the fishkeeping hobby, we all fall for the same trap! We come across those lovely discus fish in the shop and just want to purchase them.

Then we forget (or don’t know) that we need to test our water parameters before adding any fish to our tank.

If your discus fish are turning black, it could be a sign that your water is not up to par. Some water conditions that can cause discus to turn black are:

Ammonia Levels

Ammonia is one of the most toxic compounds to fish and is produced by the breakdown of organic matter in the tank (fish waste, uneaten food, plants, etc.).

When ammonia levels elevate, the fish become distressed and turn black. The fish behave in this way because they sense something is wrong but can’t put a finger on the problem.

Tank Filter

Imagine having a pile of leaves and twigs in your backyard. After a while, the leaves and twigs start to decompose and release ammonia into the air. What do you do?

You clean up the leaves and twigs, of course! The same goes for your fish tank. Your tank filter is responsible for removing the ammonia from the water before it has a chance to harm your fish.

If your filter isn’t working properly, the ammonia will build up in the water and cause your discus fish to turn black.

Water Temperature

Discus are tropical fish and prefer a water temperature between 82-86 degrees Fahrenheit. If the water is too cold, they become sluggish and will lose their brightness gradually until they turn black.

Lack of Companion

If all of the water tests come back clean, we must examine the internal conditions. This color in the fish’s body might be a result of a lack of company, but why?

Discus fish are a schooling species that requires at least four other healthy discus fish to live happily in an aquarium.

Otherwise, they will feel lonely, anxious, and worried. All of these factors can cause your fish’s mental state to go crazy, thus changing the color of their body.

Wrong Acclimation Process

When getting your new fish home, you must follow a strict acclimation process to ensure that they don’t go into shock.

If you don’t do this correctly, their bodies will go into survival mode and start shutting down non-essential functions like digestion and reproduction. This can cause them to undergo color changes, including turning black.

Attack from Bacteria, Parasites, or Fungus

Sometimes your fish tank will have an unseen invader that’s causing them to face many dangerous challenges such as bacteria, parasites, or fungus.

Sadly, you might not notice that until it’s too late and your fish are already sick and changing color.

The Parent Tank is Too Small

The discus fish spends the first several weeks of its life in the parent tank. When your discus fish outgrows this aquarium, you must move them to a larger one.

However, if you don’t do this in time, your fish will start to feel cramped, leading to a change in color.

Black-Stripe Syndrome

This disease is caused by a parasite called Cryptocaryon irritans. This parasite will attach itself to the fish and start feeding off their blood.

As the parasite feeds, it causes granulation, leading to black spots or stripes on the fish. In the end, the fish might die if they don’t receive proper treatment.

How to Treat Sick Black Coloured Discus Fish?

Quarantine the Sick Fish

When you have a sick fish or just brought new fish home, you should make sure that they don’t infect the rest of your aquarium and cause a disease outbreak in your tank.

To do this, you should put the new or sick fish in a separate quarantine tank for at least 3 weeks. This will let you see if they develop any symptoms while also allowing you to treat them without harming the other fish.

Set the Right Water Parameters of the QuarantineTank

If you transport your fish to quarantine but don’t establish the appropriate parameters, what is the point? The key to your fish’s recovery is to establish the correct parameters.

Subsequently, you must check that the quarantine tank has the water temperature, pH level, and hardness levels set correctly.

Additionally, double-check that you prepare this tank with ammonia and nitrite-free water prior to moving the sick discus fish into it.

These are the water parameters that you should establish in the quarantine tank:

Keep the Quarantine Tank Simple

Several aquarists make the mistake of over-decorating the quarantine tank. They add too many hiding places, plants, and other decorations which can stress out the fish.

Rather than the typical buildup, you should keep it simple by avoiding any substrate, plants, or decorations in your tank since discus fish may get trapped and hurt themselves. To reduce stress, I also recommend using a bare tank with little water flow.

For moderate water circulation, you can use an air stone or an aquarium filter with an output tube placed near the bottom of the tank.

Further, you should use a light-colored background for your tank (light blue is best) since your discus is more likely to remain black in a dark background.

Set Up the Parent Aquarium

In case you don’t have the funds to start an isolation tank immediately, you can clean and reset your parent aquarium. However, you should adjust the same water parameters as I listed for the quarantine tank.

To begin, you should clean off any algae, waste, and food leftovers in the aquarium. You can use a siphon hose or a scrubber to remove the algae from the glass.

After that, it’s time to rinse off all of the decorations, rocks, and gravel with fresh water. Make sure you do this outside of your house to avoid making a mess.

Also, don’t forget to clean your filter media to get rid of any parasites or diseases that might be hiding in there.

After you complete these steps, you can start setting up your parent aquarium again. First, add the gravel and then the decorations.

Next, fill the tank with treated water and then install the filter. Finally, you can add your discus fish back into the tank.

Water Change

This is the most crucial step in the process. Why? You need to remove all parasites and diseases from the water, of course!

To do this effectively, perform a water change that consists of at least 80% new water. This will help guarantee that you eliminate as many bad bacteria as possible.

To ensure the safety of your sick discus fish, you should relocate it to another location before changing 80 percent of the water. You can use a separate tank, a bucket, or even a bathtub.

Whatever you do, don’t put the fish back into the aquarium until the water has had time to sit for at least 24 hours. This will give the chlorine time to dissipate and allow the new water to reach the same temperature as the old water.

After the 24 hours pass, you can slowly acclimate your discus fish to the new water by adding a small amount of new water to its container every 5 minutes for 30 minutes.

Overall, you should stick to a regular water change schedule to keep your discus fish healthy and free of diseases. I recommend changing 20% of the water every 2 weeks.

Use Epsom Salt for Medication 

Epsom salt is a great remedy for aquarium fish. This helps to cleanse the digestive system and increase fish hunger, as well as being a muscle relaxant for cramped or injured fish.

In case your discus fish isn’t eating and begin to turn black, you can try this method to help them recover.

To do this, dissolve 1 tablespoon of Epsom salt in 1 gallon of water. Then, add this solution to your aquarium and let the fish swim in it for 30 minutes.

After that, remove the fish from the aquarium and perform a water change. You should do this treatment once a week until your discus fish is eating again and has returned to its original color.

Use Metrogyl 400 Tablet for Medication 

If your discus fish’s health does not improve after following all of these standard treatments, it is likely that your buddy is suffering from bacterial or parasitic infection.

In this situation, you will need to use medication to get rid of the infection. One of the best medications you can use is Metrogyl 400 Tablet.

To properly use this medication, mix 2 grams with 100 liters (26 gallons) of water and feed it to your fish for five days at 8-hour intervals.

Every eight hours, change half of the water in the tank after completing the reaction of the previous dosage. After cleaning your tank, give them another dose.

Within one week, they will begin to show improvement and should be back to their original beautiful color!

Last Words

Discus fish are a popular species of aquarium fish that come in a variety of colors. However, sometimes these beautiful creatures can turn black.

If this happens to your discus fish, don’t panic! In most cases, it is reversible and can be fixed with some simple home remedies.

By following the steps outlined in this article, you can get your discus fish back to its original color in no time!

If you have any questions or would like to share your own experiences with discus fish, feel free to contact us or leave a comment below!