Why Do My Neon Tetras Keep Dying?

If you are finding yourself asking the question “why do my neon tetras keep dying?” you have my sympathy. When neon tetras pass away with seemingly no explanation, it can be distressing and stressful.

Neon Tetra deaths can happen for a number of reasons. Some causes include poor water conditions, too small a tank, neon tetra disease and stress. 

Neon tetras are beautiful little fish with bright colors and a relaxing manner of schooling together. Learning how and why neon tetra deaths happen can help new and veteran fish owners alike keep their fish healthy and living longer lives.

This article goes through some of the most common reasons that your neon tetras are dying and most importantly what you can do to prevent it.

The Water

Water, as most people would expect, is a big part of keeping fish healthy. There are multiple things that can go wrong when keeping water in good condition and the chemicals stable. Below is a good guide on what to avoid, what to look out for and how to fix or prevent issues relating to water.

Changing Out Too Much Water

Conducting water changes is a routine part of tank management. However, the risks come when too much water is changed out at once. The chemistry of water is kept in balance and creates a healthy ecosystem. When a lot of water is removed and fresh put in, it harms the healthy system that was built. This shocks the neon tetras and they are often unable to handle the rapid changes. This leads to mass death in the tank. 

To prevent this, calculate how much water should be changed out at a time for the size of tank in question. A good starting rule is to change out 10 to fifteen percent of the water once a week. If the tank is well stocked, it may be safe to change out slightly more. In the case that a lot of the tank water needs to be changed out because of poor water conditions, or other scenarios, do it bit by bit. Change out part of the water and then wait a couple days before changing more.

Poor Water Conditions

Keeping high quality water in a tank is extremely important. If the water is not treated and tested regularly, things like pH levels, nitrates or ammonia can rise to dangerous levels. Having poor quality water is one of the leading causes for tetras to die. Fish evolved to live in different water conditions depending on where they would be found in the wild. Mimicking their natural habitat is the best way to ensure they live long and healthy lives.

Fish owners should set up a regular schedule to test the water and filters. If anything ever seems “off,” don’t hesitate to do an extra round of testing, Make sure to purchase a good testing kit; don’t settle for something just because it is cheaper. Spending a little more money now could save the life of fish later.

(Find out more information on how to care for neon tetras with our awesome article!)

Introduced Toxins

A small amount of foreign materials could be fatal to a school of neon tetras. This could be lotion, bug spray, soap or cleaning chemicals. Introducing a substance like those, or anything else that does not belong in a fish tank often causes tetras to die. Their bodies aren’t built to process what goes into harsh items like soap and that is what kills them.

Whenever a tank needs cleaned, use approved products and keep them separate. If a small brush is used to clean the glass, don’t ever use it for anything else that may expose it and as a result, the fish to toxins.

To keep incidents from happening, purchase a sturdy cover for the tank. That will keep items from falling into the fish tank and contaminating the water. Always make sure skin is clean and free from scented perfumes, soaps and lotions before sticking hands into the water. Don’t put things on top of the tank that could break the top and fall in.

Temperature Changes

In general, neon tetras are hardy fish. Some species of fish will suffer and die if their water varies by more than two or three degrees. Tetras can be more tolerant and like temps to be 70 to 78 degrees. 75 tends to be the sweet spot. But, sudden temp changes can be fatal, quickly. like with water conditions, tetras have evolved to live in certain water, and that includes temperature. Abrupt changes in temperature shock the fish and causes stress on their bodies that leads to death. If they don’t die, the increased stress will leave them vulnerable to disease.

These changes in temperature can be prevented by monitoring the temp in the tank at all times. Buy a good quality thermometer and stick it to the side of the tank. Keep the tank away from windows, heaters, air conditioners, vents or anything else that could influence the temperature.


It is easy to overfeed fish, especially in a smaller tank. Newer fish owners often make this error, but they shouldn’t be overly critical of themselves as it is a very common mistake to make and, fortunately, an easier one to correct.

The more neon tetras are fed, the more waste they create, which raises chemical levels in the tank. If there is uneaten food, it will sink to the bottom of the tank and rot, polluting the water. The result is that the water may become so toxic that the neon tetras die.

To prevent this, only feed the fish once a day, or every other day. Keep an eye on how much they need to eat and adapt accordingly. Seeing some uneaten food once or twice won’t cause too much harm, but be aware of it. Another way to prevent overfeeding is to use high-quality fish food that is more appetizing and swap between a couple different brands of fish-food. Add in one day a week where the neon tetras don’t eat at all.

Neon Tetra Disease

Neon tetra disease is caused by a parasite that is far more common than most people know. Unfortunately, there is no cure for neon tetra disease and as it is highly contagious among other tetras, it can quickly kill off an entire tank if not dealt with immediately.

Other species of fish can also become infected, like guppies, barbs, rasboras and ornamental species like angel fish. It is called neon tetra disease because it is most well known in neon tetras. The disease begins slow, but quickly changes to severe and then fatal.


There are a number of symptoms that will become more obvious and severe as the disease progresses. They won’t all appear every time, or in the exact order as below. Fish owners should keep a keen eye out for any unexplained behavior in their fish.

  • Coloration begins to disappear

  • Restlessness

  • The body becomes uneven from cysts forming

  • Difficulty swimming

  • Curved spine

  • Fin rot

  • Bloating

Restlessness is often the first symptom to appear. The affected fish won’t school with the others and isolate themselves, acting agitated. This is the first clear sign that they are not well. As the disease continues, the fish will lose color as their muscles turn white. If damage to the body is bad enough, the spine will become curved and cause the tetra to have trouble swimming. If the body of the tetra looks lumpy or uneven, that means cysts are forming and further harming the muscles. Sometimes bloating and fin rot happen, which means there is another infection at the same time.

To Prevent

While there is no cure and sometimes no way to keep the parasite from appearing, precautions can be taken. Keep water quality excellent, which will help to prevent parasites. Avoid buying sick fish, which is the number one reason neon tetra disease happens. Water quality is secondary. Purchase fish from reputable sellers and examine them for any signs of illness. If it is at all possible, set up a tank to quarantine the new fish in until it can be sure that they aren’t sick. If any fish ever show signs of disease, immediately separate them from the others. Doing so may prevent the entire tank from passing away.

"Why Do My Neon Tetras Keep Dying?" - Final Thoughts

Neon tetras can live up to ten years in a well cared for tank. Fish owners of all ages and experience should take the above tips into consideration and keep an eye on their water and fish. Understanding why neon tetras may suddenly die goes a long way to preventing future mistakes and learning about what their needs are. Simply taking a few minutes each day to do nothing but observe the fish can catch many issues.

Having a school of neon tetras can be rewarding and relaxing. Don’t be discouraged by the ways they can pass away. Every pet has requirements and things that have to be avoided. Take it in stride and go forward with new knowledge and skills to help the occupants of any tank live longer and healthier.