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Why Is My Neon Tetra Turning Black? (With 5 Solutions)

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Neon tetras are among the most popular freshwater fish in home aquariums and for a good reason. They are beautiful, peaceful, and get along with many other fish species.

However, sometimes they raise some concerns. That was at least how I felt when I saw that one of my neon tetras gradually turned black.

As I didn’t know what to do, I started investigating. As it turned out, there are many reasons behind this phenomenon, each with its own solution.

Is It Normal For Neon Tetras To Change Color To Black?

No, it is not normal for neon tetras to change color to black.

A change in color, especially to black, is typically indicative of stress, disease, injury, poor water conditions, or high ammonia levels in the water.

Why Do Neon Tetras Turn Black?

If your neon tera gradually becomes black, consider the following:

1. Ammonia Burns

An issue often overlooked in aquarium maintenance is the detrimental impact of ammonia burns.

A color change to a darker hue, such as black, could be a neon tetra’s reaction to the severity of this environmental stressor:

  • Excess Fish Waste: The more fish in the tank, the higher the volume of waste produced. This waste can decompose and lead to high levels of ammonia, which can be harmful for neon tetras.
  • Overfeeding: Overfeeding can lead to a surplus of decomposing food in the tank. As the food decomposes, it produces ammonia, which in high concentrations can burn the neon tetras, causing them to turn black.
  • Poor Filtration: The filter plays a crucial role in breaking down and removing ammonia from the water. If the filter is not functioning correctly, ammonia levels can spike, affecting the neon tetras.
  • Infrequent Water Changes: Regular water changes are vital to keeping ammonia levels low. Neglecting to do so can allow ammonia concentrations to rise, potentially leading to burns on the neon tetras.
  • Sudden Changes in the Population: If new fish are added to the aquarium too quickly, the sudden increase in waste may result in an ammonia spike before the tank’s biological filtration has time to adapt.

2. Physical Injury

Physical injury can trigger a color change in neon tetras, as their bodies attempt to heal the damaged tissues:

  • Aggressive Tank Mates: Other species of fish may be aggressive and physically harm the neon tetras, leading to injuries that can cause color change.
  • Sharp Objects: Decorations or substrate with sharp edges can injure neon tetras. As their bodies react and heal, they may turn black.
  • Transportation Stress: The stress and potential physical harm caused during the transportation of neon tetras can lead to injuries which may cause color changes.
  • Poor Handling: Mishandling neon tetras, especially during tank cleaning or relocation, can result in injuries leading to color change.
  • Unstable Environment: Sudden or frequent changes in water temperature, pH, or other water parameters can cause physical stress, potentially injuring the neon tetras and leading to a color shift.

3. Disease

Neon tetras are susceptible to a variety of diseases, many of which can induce a color change as a symptom of the ailment:

  • Parasitic Infections: Neon tetras infected by parasites may display a darker color as their bodies attempt to fight off the invaders.
  • Fungal Infections: Fungal spores can cause skin diseases in neon tetras, leading to discoloration and potentially turning their bodies black.
  • Bacterial Infections: Bacterial infections can affect the overall health of the neon tetra, causing the skin to darken as a sign of distress.
  • Neon Tetra Disease: This is a specific, incurable disease that affects neon tetras, causing them to lose their vibrant colors and turn black.
  • Viral Infections: Viruses can also trigger changes in a neon tetra’s coloration, indicating that the fish is ill.

4. Stress

Like many other fish species, neon tetras can change color in response to stress, which can come from numerous sources in an aquarium:

  • Overcrowding: Too many fish in a small space can cause stress for neon tetras, leading to a color change.
  • Incompatible Tank Mates: If other species of fish are aggressive or incompatible, this can cause stress to the neon tetras, resulting in color changes.
  • Inadequate Diet: Neon tetras not receiving a balanced diet may become stressed, leading to a shift in their color.
  • Poor Lighting: Neon tetras prefer dimly lit conditions. Too bright or too dark lighting can cause stress, leading to color change.
  • Lack of Hiding Spots: Neon tetras like to have places to hide. If the aquarium lacks enough hiding spots, it can stress the fish, resulting in them turning black.

Also Read: Stress In Neon Tetras

5. Poor Water Conditions

Maintaining appropriate water conditions is crucial for the health and vibrancy of neon tetras, with poor conditions leading to potential color changes:

  • Poor Water Quality: Unhealthy levels of nitrates, nitrites, chlorine, and heavy metals can cause neon tetras to change color.
  • Incorrect Water Temperature: Neon tetras thrive at specific temperatures. Deviations from this range can stress the fish and cause color changes.
  • Wrong pH Level: If the water’s pH isn’t within the ideal range for neon tetras, they may react by changing color.
  • Lack of Oxygen: Insufficient oxygen in the water can lead to the neon tetras changing color.
  • High Mineral Content: High levels of certain minerals can adversely affect neon tetras, causing them to change their color to black.

Also Read: Why Do Neon Tetras Twitch?

What To Do If Your Neon Tetra Is Turning Black

Fortunately, dealing with a blackening neon tetra is pretty straightforward:

1. Treating Ammonia Burns

When dealing with ammonia burns in neon tetras, quick action and diligent water management can support recovery and prevent further harm. Here are the steps:

  • Regular Water Changes: To manage ammonia levels, perform regular water changes. This helps dilute the ammonia present, reducing the risk to neon tetras.
  • Proper Filtration: Ensure the aquarium’s filter is functioning well. A properly working filter can break down and remove excess ammonia, making the environment safer for neon tetras.
  • Avoid Overstocking: Keep the number of fish per gallon within recommended limits to minimize fish waste production, thus controlling the ammonia levels for the neon tetras.
  • Control Feeding: Prevent overfeeding as excess food can decompose and produce ammonia, posing a risk to neon tetras.
  • Test Water Regularly: Regularly testing the water allows early detection of rising ammonia levels, enabling prompt action to protect the neon tetras.

When testing the water, ammonia should be at 0 ppm. Keep making water changes until there is absolutely no ammonia in your tank.

As for a testing kit, I personally use the API FRESHWATER MASTER TEST (link to Amazon). I found it to be the most cost-effective and reliable.

You should also consider the Tetra AquaSafe (link to Amazon), which prepares tap water for fish. Avoid using tap water without proper conditioning.

Also Read: Neon Tetra Tank Setup

2. Managing Physical Injury

Physical injury in neon tetras can be addressed by creating a safe and gentle environment within the aquarium. Here are some measures:

  • Appropriate Tank Mates: Ensure neon tetras are kept with compatible, non-aggressive species to prevent harm and injuries.
  • Safe Decorations: Choose aquarium decorations without sharp edges. This prevents the neon tetras from getting injured.
  • Gentle Handling: Handle neon tetras gently, especially during cleaning or relocation to avoid causing injuries.
  • Quarantine New Fish: New fish should be quarantined before introducing them to the main tank. This prevents the spread of diseases and reduces stress-related injuries to neon tetras.

Also, consider adding the API Stress Coat (link to Amazon) to your tank. This product protects exposed fish tissues from infections.

I would also suggest avoiding aggressive tank mates like:

  • African cichlids (various species, such as Mbuna cichlids from Lake Malawi)
  • Jack Dempsey (Rocio octofasciata)
  • Green Terror (Andinoacara rivulatus)
  • Convict Cichlid (Amatitlania nigrofasciata)
  • Jaguar Cichlid (Parachromis managuensis)
  • Red Devil Cichlid (Amphilophus labiatus)
  • Oscar (Astronotus ocellatus)
  • Flowerhorn Cichlid (Hybrid cichlid)

Prioritize peaceful fish that aren’t likely to harras your neon tetras, such as:

  • Celestial Pearl Danio (Danio margaritatus)
  • Ember Tetra (Hyphessobrycon amandae)
  • Pygmy Corydoras (Corydoras pygmaeus)
  • Cardinal Tetra (Paracheirodon axelrodi)
  • Endler’s Livebearer (Poecilia wingei)
  • Cherry Barb (Puntius titteya)
  • Glowlight Tetra (Hemigrammus erythrozonus)
  • Harlequin Rasbora (Trigonostigma heteromorpha)

Also Read: 19 Great Neon Tetra Tank Mates

3. Treating Disease

Disease in neon tetras can be combated with proactive detection, adequate treatment, and prevention of future outbreaks. Here’s how:

  • Identify Symptoms: Early identification of symptoms can lead to prompt treatment, improving the chances of recovery for neon tetras.
  • Medicate Appropriately: Depending on the diagnosis, use the appropriate medication. Always follow dosage instructions to avoid harm to the neon tetras.
  • Quarantine Sick Fish: Neon tetras showing signs of illness should be quarantined to prevent disease spread in the main tank.
  • Maintain Cleanliness: Regularly clean the aquarium to prevent the build-up of disease-causing organisms, ensuring a healthier environment for neon tetras.

Also Read: 17 Neon Tetra Diseases & Their Treatments

4. Reducing Stress

Reducing stress in neon tetras requires creating an environment that caters to their specific needs and ensures their well-being. Here are the steps:

  • Provide Adequate Space: Ensure the tank is spacious enough to prevent overcrowding, reducing stress for neon tetras. I usually suggest 20 gallons for a group of at least 6 neon tetras.
  • Compatible Tank Mates: Choose tank mates compatible with neon tetras to prevent aggressive interactions, which can cause stress.
  • Balanced Diet: Provide a balanced diet to fulfill the neon tetras’ nutritional needs, helping to reduce stress.
  • Proper Lighting: Maintain appropriate lighting levels in the tank to suit the preferences of neon tetras and reduce stress.
  • Provide Hiding Spots: Incorporate enough hiding spots in the aquarium for the neon tetras to retreat to when they feel threatened.

Also Read: Why Is My Neon Tetra Turning White?

5. Improving Poor Water Conditions

Improving water conditions in a neon tetra tank involves regular monitoring and adjustments to maintain the parameters within acceptable limits. Here are the steps:

  • Regular Water Tests: Regularly test the water for parameters like pH, temperature, and harmful substances to keep the environment safe for neon tetras.
  • Frequent Water Changes: Perform weekly water changes of 15-20% to maintain water quality, ensuring the health of neon tetras.
  • Appropriate Temperature: Maintain the correct temperature range suitable for neon tetras. Aim for 72-78°F (22-26°C).
  • Use Water Conditioner: Use a water conditioner during water changes to neutralize harmful substances like chlorine and heavy metals, providing a safer environment for neon tetras.
  • Adequate Oxygenation: Ensure the tank has sufficient oxygen, either through an air pump or live plants, for the neon tetras. My recommendation: Hygger Aquarium Air Stone (link to Amazon).

Also Read: Do Neon Tetras Need An Air Pump?


Neon tetra shouldn’t change their color to black. If they do, you should check what caused this to prevent health deterioration.

Start with the water parameters, with ammonia in particular. Ammonia burns are usually red, but in some cases, they can appear black (especially when the wound is healing).

If you feel uncertain about your situation, I highly suggest consulting an aquatic veterinarian. An expert will guide you and provide you with the most accurate solution.