7 Reasons Your Tetras Keep Dying (+ How to Save Them)

Watching your tetras consistently die is a frustrating and heartbreaking experience. Despite your best efforts and intentions, the tetras in your care might still be falling victim to a variety of deadly problems.

So, why do my tetras keep dying? Your tetras might keep dying for a variety of reasons:

  • Unhealthy water quality
  • Insufficient tank maintenance
  • Overcrowding of your tank
  • Excess stress
  • Overfeeding
  • Cold water temperature
  • Contagious illness

This article will help you figure out which of these potential issues is causing your tetras to keep dying. It will also help you solve these issues and create a healthy aquarium environment in which your tetras can live long and happy lives.

Unhealthy water quality

One reason your tetras might be dying is that the water in your tank is toxic and unhealthy. In order to maintain healthy water quality and lengthen the lifespan of your tetras, you first need to understand how the chemistry of aquarium water works.

Aquarium water chemistry: a basic overview

The water quality in your aquarium is largely determined by how you process the waste in your aquarium. This waste can include fish droppings, uneaten food, deceased fish, and excess plant matter. These kinds of biological waste will release ammonia, which is poisonous to fish.

Once ammonia is in the water, a type of bacteria called Nitrosomonas converts the ammonia into nitrite. Nitrite is also toxic to tetras, but fortunately the conversion process does not end here. Another type of bacteria, Nitrobacter, converts the nitrite into nitrates. While prolonged exposure to Nitrates can cause health problems in tetras, they are much less toxic than nitrate and ammonia.

The nitrate level in your aquarium water is typically kept in check with aquatic plants, frequent water changes, filtration, and a conservative feeding strategy.

New Tank Syndrome

One of the most common causes of tetra death is New Tank Syndrome, which occurs when ammonia and nitrite levels rise to dangerous heights. While ammonia and nitrite are typically kept in check by nitrifying bacteria, new tanks often don’t have enough bacteria to keep the ammonia and nitrite levels in check.

So if you’ve just installed a brand new tank with brand new gravel and a clean and fresh filter, you need to be extremely cautious about adding new fish into the community. The nitrifying bacteria need time to reproduce and spread. If you add too many sources of biological waste (AKA too many new fish) at once, the bacteria won’t be able to handle all of the ammonia and nitrite they produce, and your tetras may die as a result.

Other sources of water contamination

Ammonia isn’t the only thing that can poison your fish. Plenty of foreign materials and substances can turn your aquarium water into a toxic pool.

One common example is cleaning liquid that can contaminate your tank during a water change. If you use a bucket or bowl during your water changes, make sure you only use that bucket or bowl for every single water change. You should also make sure to never wash this bucket or bowl with cleaning liquids, as even the tiniest bit of cleaning liquid can mix with your tank water and cause irreparable harm to your fish.

Another common toxin in tank water is chlorine. If you use tap water that has been chlorinated, you run the risk of poisoning your tetras with excess amounts of chlorine. The easiest way to make tap water safe for your fish is to condition it with a dechlorinating substance. If your tap water has chlorine in it, you can use this API Tap Water Conditioner (available on Amazon) to remove the chlorine and make the water from your faucet aquarium-friendly.

Insufficient tank maintenance

Regular water changes and tank cleaning sessions will go a long way toward improving the lives of your tetras. Fish waste and uneaten food can build up surprisingly quickly. If you don’t change your water and vacuum your gravel on a weekly basis, the water quality can quickly become unhealthy and toxic. This is especially true of new tanks, as ammonia and nitrite levels will rise more quickly than normal due to the lack of nitrifying bacteria.

Overcrowding of your tank

Adding too many tetras to a small tank is a straightforward way to spike the ammonia levels in your aquarium. Fish waste is the biggest source of ammonia in your tank, and adding a bunch of fish at the same time can quickly overwhelm the nitrifying bacteria that keeps your community safe.

As a result, you should be cautious and methodical about adding new members to your freshwater community. Only introduce a few new a few at a time, and give your tank and your fish ample time to adapt to the increased population.

Excess stress

As humans with particularly resilient immune systems, we don’t often equate stress with an increased risk of death. However, extended periods of stress can weaken both your and your tetras’ immune system, and your tetras are much more fragile than you are. As such, you need to do all you can to keep your tetras’ stress level at an absolute minimum. If you don’t, they are more likely to get sick ‒ and they will have a harder time fighting off the illness than if they were in a calm and peaceful state of mind.

Here are a few ways you can lower your tetras’ stress levels:

  • Don’t place your hands in the tank unless you absolutely need to. Large human hands can look like a hungry predator to a tetra, and they can get anxious and frightened at the sight of them.
  • Don’t scare your tetras with loud noises. This includes tapping on the tank walls, playing loud music, yelling near your aquarium, and any other loud sounds that might scare your fish.
  • Don’t house your tetras with known bullies. Some fish love to nip and bite at other fish, and this constant harassment can create a permanently heightened level of anxiety in your tetras.


Overfeeding is one of the most common causes of premature tetra death. While it’s surprisingly easy to place too much food in your tank, you need to be careful about doing so. The danger actually isn’t in your fish eating too much ‒ it’s in uneaten food decomposing at the bottom of the tank and increasing the ammonia levels in the water.

While the easiest way to fix this issue is to only give your fish enough food for five minutes of munching, there are a few other ways you can deal with excess food rotting at the bottom of your aquarium:

  • Get a bottom feeder fish. They will scour the gravel at the bottom of your tank and suck up any food they find.
  • Change your water regularly. While this won’t get rid of any food sitting in your tank, it will reset the heightened ammonia levels in the water back to normal.
  • Clean out any uneaten food when you change the water.

Cold water temperature

Tetras are tropical fish, and they need a sufficiently warm tank in order to thrive. They are also cold-blooded, so they rely entirely on warm water to regulate their metabolism.

Tetras prefer water that is between 75 to 78 degrees Fahrenheit. To maintain this temperature, you can use a submersible aquarium heater (available on Amazon) to keep your water temperature at a steady and livable level.

Contagious illness

Contagious illness is one of the scariest parts of owning a community fish tank. If one fish gets sick, your entire aquarium is also at risk. Fortunately, there is a lot you can do to prevent, detect, and cute contagious illnesses before they decimate the tetras and other fish in your community.

If you’re concerned that your tetras are sick, you can read this guide on tetra diseases and treatment from AquariumInfo.org.