Why Are My Neon Tetras Dying?

Neon tetras are delightful pets with brilliant colors and soothing swimming motions.

Fish owners may become distressed when their fish die for no apparent reason. Understanding the most common causes of neon tetras’ deaths can help you prevent future mishaps in the tanks. 

So, why are your neon tetras dying? Several reasons cause neon tetras to die. Some of them include stress, poor water conditions, and incorrect aquarium size. Another leading cause is neon tetra disease, found mostly in neon fish.  

In this guide, I will get into detail with all the reasons why neon tetras die.

Why Are My Neon Tetras Dying?

Your neon tetra’s dying causes can range from Neon Tetra Disease to the water conditions and temperature. Let’s read on to find out more.

New Tank Syndrome

Heavy concentrations of ammonium and nitrates in the water can be fatal. Appropriate water chemistry helps support healthy neon tetras. Natural bacteria in the water can balance out these contaminants, but fish may die before achieving that balance.

Neon tetras aren’t the only organisms that live in aquariums. A healthy fish tank also has a vibrant bacteria colony. They live all over the aquarium but are most concentrated in the filter and gravel. These microorganisms help break down the waste in the fish tank and keep the water healthy.

They have a symbiotic relationship with neon tetras. Without the neon tetras (and their food), the microscopic bacteria colony declines. Without the bacteria, the water becomes unsuitable for the fish. Keep the two in balance to avoid new tank syndrome.

To Prevent: Test your new tank regularly for ammonium and nitrate levels, and change water to reduce high levels of these components to make it safer for neon tetras.

Rapid Water Changes

Water chemistry in a healthy tank is suitable for resident fish, plants, and bacteria. Quickly changing massive quantities of water can disrupt the natural chemistry and shock neon tetras, causing unexpected death. You need to change the water occasionally, but sudden changes can be harmful.

To Prevent: Change the water slowly, swapping small quantities at a time and waiting 3-4 days before changing more water so your neon tetras can adapt to gradual chemistry changes.

Poor Water Conditions

The water quality in a tank is a key factor in fish health. Check out water salinity levels, pH levels, filtration efficiency, and other quality issues. Any one of these factors can be responsible for dead neon tetras.

Keeping the water healthy for your neon tetras is critical to avoid premature death. It’s a great idea to have a testing kit to identify your water parameters. These kits measure nitrates, ammonia, and pH levels. We recommend using the API Freshwater Master Kit, which gives accurate results.

To Prevent: Research the appropriate water conditions for your fish and take steps to maintain suitable levels to safeguard neon tetras’ health. For freshwater tanks, you want to keep the ammonia and nitrite levels at zero and the nitrates below 20 ppm.


Stress is one of the most common causes of death for neon fish. Managing stress is a pivotal part of keeping your fish healthy. Several factors impact the stress level of your neon tetras.

But how can you tell if your fish are stressed? Here are some typical signs and symptoms you can look out for:

  • Glass Surfing: This is when your fish repeatedly and frantically swims up and down the sides of the aquarium. It means that the fish wants to go outside the tank, but it can’t. The aquarium may be small and overcrowded, forcing the fish to glass surf.
  • Excessive Hiding: Neon tetras hide when they are uncomfortable or scared. They also hide because of bullying by other fish. Make better stocking choices, and buy a full-sized tank to avoid territorial issues. Be aware that it is normal for some fish types to hide, such as catfish and loaches.
  • Weight Loss: You can visibly notice if your neon tetra is losing weight. This can happen even if you are feeding them well. Fish normally stop eating because of excessive stress.
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To Prevent: Change the water regularly to keep nitrate and ammonia levels low. Check the water temperature to prevent stressful fluctuations.


Overfeeding is another big problem in small fish aquariums. The more you feed your neon tetras, the more waste they produce. Uneaten fish food decays, fouling the water. Your bacteria colony can help balance out the water chemistry, but the toxic environment may kill your neon tetras.

Go easy on flake foods and offer them sparingly. You can introduce a fasting day every week, where the neon tetra don’t eat at all. Some fish owners like to include veggies, freeze-dried foods, and thawed frozen foods like blood worms.

To Prevent: Feed your fish once every day and avoid overfeeding. Choose quality fish food or alternate between different brands. Make sure to add sinking pellets for the scavengers and algae wafers for plecos.

Temperature Changes

Most neon tetras can tolerate a range of temperatures in the fish tank, but sudden temperature changes can cause stress, making them more susceptible to illness. Very dramatic changes can be quickly fatal.

To Prevent: Check the new tank heater for proper function every day. Position your tank away from anything that might raise or lower its temperatures, such as heating or cooling vents, sunny windows, or drafty places.

Unexpected Toxins

Even tiny amounts of toxic contaminants can be fatal to neon tetras, such as bug spray, hand lotion, perfume, soap, and cleaning chemicals. If the water becomes contaminated with these substances, neon tetras will suffer.

To Prevent: Protect your tank from unintentional contamination by using a cover. Keep unwanted toxins away from the tank, and always wash your hands with unscented, non-antibacterial soap before accessing it.

Neon Tetra Disease

Neon tetra disease is a condition caused by a Microsporidian parasite that’s more common than aquarium enthusiasts realize. It is a degenerative disease, which means it starts off slow but progresses quickly to become severe. This disease is one of the leading causes of dying neon tetras. Understanding the symptoms and causes of neon tetra disease can help prevent it.

Symptoms of Neon Tetra Disease

In neon tetra disease, you will observe these symptoms:

  • Restlessness
  • Neon tetras begin to lose coloration
  • As cysts develop, the body becomes lumpy
  • Neon tetras have difficulty swimming
  • In severe cases, the spine may become curved
  • Secondary infections such as bloating and fin rot
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During the initial stages of neon tetra disease, the only symptom may be restlessness. Often the first thing you will notice is that the affected fish isolate themselves—a clear sign that they’re suffering.

As the condition progresses, affected muscle tissue being to turns white, and the pale coloration expands. Damage to the muscles can cause deformation or curvature of the spine, which causes the fish to have difficulty swimming. You might also notice a lumpy appearance on your neon tetra as the cysts deform muscle tissue.   

Rotting of the fins and bloating are not uncommon, but they indicate a secondary infection.

Causes of Neon Tetra Disease

Pleistophora hyphessobryconis parasite is the main culprit behind neon tetra disease. If your neon tetras feed on infected live foods, they may serve as intermediate hosts.

Once inside a neon tetra, the parasite will eat it from the inside out. It begins with the digestive tract and stomach. Sporoplasms can develop inside the intestines and produce cysts. The cysts damage the muscle tissue; signs of tissue damage include weaker muscles and paler color.

It’s crucial to know neon tetra disease is highly contagious and can quickly spread through a tank. To save your neon tetras, you will need to remove infected fish as soon as possible.

To Prevent: The best prevention is to avoid buying sick fish and maintaining high water quality. It’s also important to remove sick fish from your community aquarium. There is no real cure for neon tetra disease, but you can take preventative measures.

When purchasing neon tetra for your tank, select a well-reputed supplier. If buying online, be sure to read reviews and avoid purchasing for price versus quality. Whenever possible, buy locally. This will allow you to observe the suppliers’ fish. Do not purchase any fish from community tanks with sick, dying, or dead fish present; you can identify a sick fish because it usually isolates itself. 

Frequently Asked Questions

Can neon tetras die easily?

Neon tetras can live up to ten years, but they can die easily with the slightest change in the fish tank environment. If there are any drastic changes in the water chemistry, the fish begin experiencing stress and depression, and develop low immunity.

Do neon tetras need a water heater?

Neon tetras are tropical fish and require a heater that keeps the tank at about 72–80 degrees Fahrenheit. Additionally, they need a filter to provide a home for beneficial bacteria and to clean the water.

Do neon tetras sleep at night?

Like other tropical fish, tetras require darkness to complete the circadian rhythm. So, they will sleep at night in complete darkness and become active during the day.

Do tetras need a bubbler?

Air pumps promote aeration, but they are not necessary for neon tetras. Bubblers force oxygen into the aquarium so fish can breathe. In most cases, neon tetras don’t require extra oxygen.  

Do neon tetras glow in the dark?

Neon tetras look brilliant under the glow of a black light. The shiny blue stripe on their body glows, creating a unique light show for the viewer. The clear skin of a neon tetra creates a fluorescent glow under a black light.

Final Thoughts

Keeping neon tetras can be a great experience, and knowing why they die can help you avoid the most common causes of aquarium fish deaths. Observe your neon tetras regularly and notice their swimming behavior.

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Nadine Oraby

My name is Nadine; I am a passionate writer and a pet lover. People usually call me by the nickname “Joy” because they think that I am a positive and joyful person who is a child at heart. My love for animals triggered me to create this blog. Articles are written by vets, pet experts, and me. Thanks for visiting. Your friend, Nadine!

1 thought on “Why Are My Neon Tetras Dying?”

  1. My neon is at the top of the water at all times away from the other 7. I got a tank that is too hard to keep care of. Now only 3 neons including him.


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