Black Spots On Neon Tetras: Causes & How To Treat Them

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Neon tetras are an excellent addition to fish tanks. They are both peaceful and beautiful, making them one of the most popular choices among aquarists.

However, they often present worrying signs. A few months ago, I noticed one of my neon tetras had developed what looked like black spots on its gills.

After extensive investigation and research, I discovered several reasons for this issue and learned how to solve it. Today, I’ll share everything I learned with you.

Let’s dive in.

Why Do My Neon Tetras Develop Black Spots?

Observing dark patches on your neon tetra can be attributed to various factors:

1. High Ammonia Levels

Ammonia, a typical byproduct resulting from fish excrement and leftover food, can accumulate in your fish tank.

If the levels become excessively high, it can cause a harmful condition known as ammonia poisoning.

This can manifest as changes in color, such as black spots, as well as lethargy, gill discoloration, and rapid, labored breathing.

Regular testing of your water for ammonia levels, good filtration, and regular water changes can help prevent this.

2. Black Spot Disease

Also known as Diplopstomiasis, black spot disease is caused by a parasite and is named for the black spots that appear on the fish’s body.

The spots are actually cysts where the parasites have burrowed under the skin.

This disease often affects outdoor ponds and is more prevalent when the water hosts snails, the intermediate host of the parasite.

Treatment involves anti-parasitic medications and reducing the snail population.

3. Healing from an Injury

Fish can change color as a response to stress or injury.

If your neon tetra has suffered a recent physical injury, it may develop black spots at the site of injury.

This is a natural response and part of the healing process. Keeping the water clean and avoiding further stress can help the fish recover.

4. Genetics

Some neon tetras may have black spots due to their genetics.

This is often the case when the black spots have been present since birth and don’t cause any apparent distress to the fish.

There’s not much that can be done in this case, as it’s just a part of the fish’s natural coloring.

However, breeders often select against this trait, so it’s less common in commercially bred neon tetras.

Also Read: 17 Neon Tetra Diseases & Their Treatments

How To Treat Neon Tetras With Black Spots

If you notice black spots on your neon tetra, it is likely that treatment will be necessary. Here’s what you should do if treatment becomes necessary:

1. Dealing With Ammonia Poisoning

  • Test your water: Purchase a water testing kit to check for elevated levels of ammonia. These kits are usually available at pet stores.
  • Water change: If ammonia levels are high, perform a partial water change, removing around 20% to 50% of the water and replacing it with clean, dechlorinated water.
  • Adjust feeding: Overfeeding can contribute to high ammonia, so ensure you are not providing more food than your fish can consume.
  • Examine your filter: Make sure your aquarium’s filter is working correctly as it plays a vital role in controlling ammonia levels. Consider upgrading or adding another filter if necessary.
  • Use ammonia neutralizers: There are products available in pet stores that can neutralize ammonia in the water. My recommendation: API Ammo Lock (link to Amazon).

2. Treating Black Spot Disease

  • Identify the disease: Black Spot Disease is characterized by small black dots on the fish. It is caused by a parasite that often comes from snails.
  • Treat with medication: Use an anti-parasitic medication designed for aquarium use. Follow the instructions carefully.
  • Remove snails: If possible, remove any snails from your aquarium, as they are the intermediate host of the parasites causing the disease.
  • Water change: Regular water changes can help prevent the disease from returning.

3. Healing From Injuries

  • Identify the injury: Observe your fish regularly and see if you notice any wounds or unusual behavior.
  • Minimize stress: Provide a stress-free environment by maintaining the right temperature and pH, feeding your fish a balanced diet, and providing plenty of hiding spaces.
  • Water quality: Maintain clean water in the tank to prevent infections in the wound. Regular water changes and a functioning filtration system can help with this.
  • Consider medication: If the injury doesn’t seem to heal or worsen, consider using a safe, aquarium-specific antibacterial or antifungal treatment. My recommendation: API Stress Coat (link to Amazon).

Also Read: Neon Tetra Fin Rot

4. Genetics

  • Understand that if the black spots are genetic, there may be no “problem” to solve. Genetic spots do not harm the fish or affect its quality of life.
  • If you’re breeding neon tetras and don’t want this trait to pass on, select fish without these spots for breeding.

Preventing Black Spots On Your Neon Tetras

To minimize the chances of your neon tetra developing dark patches, you can follow these steps:

  • Regular Water Changes: Regular water changes, typically 20-25% every week or two, can help to prevent the buildup of waste, uneaten food, and toxins, including ammonia. This can reduce the likelihood of ammonia poisoning and the resulting black spots.
  • Maintain a Clean Aquarium: Regular cleaning of your aquarium helps to maintain a healthier environment for your fish. This includes removing uneaten food, cleaning the substrate, and scrubbing off any algae build-up. A cleaner aquarium reduces the chance of diseases like Black Spot Disease.
  • Ensure the Aquarium is Adequately Sized: Neon tetras need sufficient space to swim and grow. Overcrowding can lead to increased stress and a higher risk of disease and injury. As a rule of thumb, a 20-gallon tank is recommended for keeping neon tetras.
  • Use A Filter: A good filter is essential for maintaining water quality. It removes waste, toxins, and can help control ammonia levels. Additionally, filters also help in maintaining oxygen levels, which is crucial for the health of your neon tetras.
  • Quarantine Sick Tetras: If you notice a fish showing signs of illness or disease, it’s a good idea to quarantine them in a separate tank. This prevents the spread of diseases like Black Spot Disease and protects your other fish.
  • Ensure Adequate Lighting: Neon tetras thrive with a proper day/night cycle and subdued lighting. Too much bright light can cause stress and potential health issues. Using a timer for your lights can help simulate a regular day/night cycle and keep your tetras comfortable and healthy.

Also Read: Neon Tetra Constipation


Here’s a concise summary of the key points I discussed earlier:

  • Black spots on neon tetras can indicate various underlying issues, including high ammonia levels, disease, healing from injuries, or genetics.
  • Treating ammonia poisoning and addressing water quality is crucial to prevent and remedy dark patches on neon tetras.
  • Prompt treatment and quarantine are necessary if a neon tetra is affected by Black Spot Disease or other illnesses.
  • Regular maintenance, including water changes, cleanliness, and adequate tank size, helps prevent dark patches and promotes the overall health of neon tetras.
  • Monitoring additional signs, such as white patches, fading color, white gills, golden patches, or red patches, is essential for the early detection of potential health problems in neon tetras.