Why Is My Cardinal Tetra Keep Dying?

Cardinal Tetra Keep Dying

You just bought some beautiful Cardinal Tetras to keep in your tank. The next day, you find them floating upside down in your tank; they’re all dead. Time and again, you find your Cardinal Tetras dying for no reason. “What’s wrong? Why do my Cardinal Tetra Keep Dying?” you ask yourself.

To help you understand why your Cardinal Tetra keeps dying, I came up with many mistakes you might’ve made while the caring process.

It might be that you didn’t recycle your tank before keeping your Cardinal Tetra. Poor water conditions or extreme fluctuation of water parameters might have messed up your Tetras health. Overfeeding, overcrowding, rapid water changes, stress, and diseases might be the reasons why your Cardinal Tetras keep on dying in your tank. 

In this article, I’ve listed every reason as to why your Cardinal Tetra seems to be dying, and also the solutions to those problems. Without further ado, let’s start.

Reasons Why Your Cardinal Tetras Keep Dying And Ways To Prevent Them

I’ve compiled a long list of reasons why your Cardinal Tetra keeps dying. If you find that you’ve made any mistakes like below, go through the solution so that you can prevent further death of your fish buddies.

New Tank Syndrome

So, this is the commonest mistake that you might make!

See, the aquarium you just bought harbors not only your Cardinal Tetra but also tiny microorganisms. These beneficial bacteria help to convert your Tetra’s wastes into harmless compounds and keep the water healthy. (Tetras wastes have high ammonia which is poison to your fish.)

In your brand new tank, there is no such microscopic colony yet. So, if you go around adding your Cardinal Tetra in this tank, there will be no beneficial bacteria to make water healthy. This results in an ammonia spike in your tank. And ultimately, your Tetras will die overnight or slowly within a week.


If you’re a newbie in fish keeping, you should definitely research the nitrogen cycle. You should “cycle” your tank before keeping your Cardinal Tetras in it.

Rapid Water Changes

In a well-balanced tank where all the fish, microorganisms, and plants are living in harmony, you can create tornadoes by performing rapid water changes. Your aquarium is a small ecosystem, you see. And disrupting this ecosystem by swiftly changing everything at once is unsettling and stressful to your Cardinal Tetra.

Cardinal Tetras are hardy fish. But, this doesn’t mean that you experiment with extreme temperature, pH, salinity, tap water, and so on with your Cardinal Tetra.

For example, you decide to suddenly change 75% of water in a day. Or you decide to increase the temperature by 20 degrees. Or you decide to add baking soda to increase pH. Well, the bad news is you’re disrupting the ecosystem of your tank. It may shock your fish and even cause death.


This is also the reason why you should acclimatize your Cardinal Tetra before keeping it in your tank.

Every change should be slow and steady in your tank. And always maintain the water parameters that your Cardinal Tetra will thrive in. 

Adjust the pH of your tank for Cardinal Tetra.

Thinking of increasing the temperature of your tank? Increase the temperature slowly and only at a temperature that your Tetras will thrive in.

Poor Water Conditions

Just remember that bad water means dead fish, sooner or later.

A Stable aquarium doesn’t fluctuate that often. But, fishbowls and aquariums with no heaters or filters are prone to bad water conditions. There may be wild swings of pH, temperature, salinity, ammonia spikes, and so on in an unstable aquarium. This is harmful to your Cardinal Tetra and maybe the reason why they seem to die for no reason.


Always check the pH, temperature, nitrogen, ammonia, levels in your tank. A pH of 4.5-7, a temperature of 73-81 Fahrenheit are ideal for your Cardinal Tetra.

There are many test kits available that will check the parameters for you.


Now, this is also the most common mistake that you might make.

See, whatever goes in your Tetra’s mouth also needs to come out. The more food you give, the more wastes are produced. As a result, it will foul your tank. The beneficial bacteria will have a hard time converting these wastes to good water. Also, excess uneaten food fouls your tank even further and produces ammonia and nitrogen.

Overfeeding may be the reason why your Cardinal Tetras are dying.


Cardinal Tetras benefit from eating once or twice a day. That too, in a small amount. Feed your Cardinal Tetras only what they can eat in under 3 minutes. If excess food remains at the end of 3 minutes, scoop the extra food with a net.

If you’re worried your Tetra is getting less food. Why not provide a nutritious diet? So that, the food they eat actually benefits them rather than giving huge junks of filler foods. High-quality flakes, pellets, blood worms, veggies are some variations you can make in your diet.

Note: Fasting is actually far more beneficial than overfeeding.


Everything I’ve mentioned in this article from bad water conditions, overcrowding, unclean tanks, bad tank mates, everything stresses out your Tetra.

Mostly, stressed Cardinal Tetra swims up and down the side of the tank. Stressed Tetra also hides behind plants or caves when they’re threatened by tank mates. Your Cardinal Tetra seems to lose weight and appears thin and weak. So, it becomes susceptible to diseases. As a result, death occurs.


Just look at the signs of stress and check what’s wrong with your tank. Is the water bad? Are you overcrowding your tank? Or maybe you’re keeping cardinal tetras with bad tank mates.

Go through this article and find out why your Cardinal Tetra is so stressed. After you’ve corrected the underlying cause of stress, your fish will be happy. There will be less death this way.


An overcrowded tank is a death ground. Well. How much work can a limited colony of beneficial bacteria do? After overworking, they burn out too.

With so many fish, there will be a large amount of poop. The beneficial bacteria can’t keep up with so much poop. This results in an ammonia spike. And this may be the reason why your Cardinal Tetras are dying.

Moreover, there is a lack of oxygen in a small tank. Because every Tetra needs to breathe but there is limited oxygen, your fish will suffocate slowly and die.


See, the larger the tank, the larger the beneficial bacteria to cut down the wastes. If you keep calculated Cardinal Tetras in a small tank, the bacilli can convert all that waste into good water.

Since Cardinal Tetra grows up to 2 inches and needs to be kept in groups (schooling fish needs a group to survive), you need at least 20 gallons of water for 4-5 Cardinal Tetras. If you don’t have a tank of such capacity, I recommend you get Cardinal Tetras. Because overcrowding will be a death sentence to them.

Incompatible Tank Mates

Cardinal Tetras are a friendly species of fish harming no one. Instead, other fish will harm and eat them up. Especially territorial, aggressive and fin nippers are big enemies of Cardinal Tetras. This stresses out your Tetras, even injuring some of your Tetras which may be the reason why they’re dying.


Well. The solution for this is simply keeping compatible tank mates for your Tetras. Research about bad tank mates to avoid. Some of the good tank mates are:

  • Neon Tetras
  • Zebra Danios
  • Hatchet fish
  • Mollies
  • Dwarf Gourami
  • Angelfish
  • Guppies

Buying Unhealthy Fish

Some fish shops are scammers who give novice fish owners unhealthy fish. If you are buying Cardinal Tetras from the shop at a low price, chances are something is wrong with the Tetra already.

Most shops also reduce the price of stressed out, sick, or fish who are bought up in poor tank conditions. And such Tetras die easily. These fish also infect the healthy fish in your tank which may be the cause of all your Cardinal Tetras dying.


If this is the case, always buy your Cardinal Tetra from reputable breeders. Also, knowing the signs of diseased stress, and unhealthy Cardinal Tetra may make you avoid buying such Tetras in the future.

Unexpected Toxins

You may clean the tank wall with bleach, dish soap, and so on. Or you may end up using bug spray to kill the insect floating at the top of your tank.

But remember. Toxins like dish soap, perfumes, lotions, creams, bleach, gasoline, bug sprays, are harmful to your fish.


Well. The solution is to avoid these chemicals and toxins. Don’t clean your tank with soap or gasoline, bleach, etc. Also, don’t try to grab your fish after moisturizing your hand with cold cream. If you think spraying perfume in your tank will remove the fish odor, it will. But, all it does is kill your fish slowly but surely.

Bad Tank Management Practices

A well-balanced aquarium rarely requires your intervention for keeping it clean. Maybe, once a month, you can dedicate a one hour time to check if everything is alright or not.

Many fish owners let the beneficial bacteria, shrimps, and cleaning fish do their job. But, hey, at the end of the day, you need to look after your tank too.

Frequent Water Changes

Now, frequent water changes mean that you need to remove 25% of the water every 2 weeks to clean your tank. This ensures that you’re diluting waste chemicals and keeping freshwater for your Tetras.

But, too many changes can harm your fish. Too many water changes reduce the good bacteria in your tank. So, this may be the reason why your Cardinal Tetra is dying.

Vacuum The Floor

Uneaten food, fish wastes, live in the gravel of your tank. And the good bacilli live there too.

But, vacuuming once every 2 weeks is beneficial. Your Cardinal Tetra can’t clean the gunk inside the floor, you see. So, you do this job.

Clean Algae

Algae growth is not rare in an aquarium. Although some fish in the wild eat alga, Algae is actually bad for your tank’s ecosystem.

Algae feed the pest snails and create a hullaballoo in your tank. So, it’s better to remove them with your hand. Or use scrapers and scrubbers to remove them.

Filter Maintenance

Now, filters have beneficial bacteria living in them. So, ditching these filters will only cause harm. So, try to Ditch your filters only after they’re worn out or if the manufacturer recommends so.

I try to replace the activated carbon monthly though! And I use sponges on my filters so they run for a long time and effectively so.


You will want to get familiar with diseases that Cardinal Tetras suffer from. Look. Cardinal Tetras are hardy. But, stress, bad water parameters, and other factors will affect your Cardinal Tetras to such an extent that their immune system lowers down.

A lower immune system will make it easier for parasites to infect your Cardinal Tetras so they die from diseases.


Well, the solution to diseases is to research Cardinal Tetra’s diseases. And then provide antibiotics, anti-parasites, and maintain good environmental conditions to make your Tetra calm down.

Search for any unusual symptoms. Does your cardinal Tetra have white spots on its body? Is your cardinal Tetra swollen? Do you see inflammation of the gills or mouth? Is your Tetra doing labored breathing? If you see such unusual signs and give medicine and treatment accordingly.  

Old Age

Finally, there is old age. For a beginner, this reason is not the answer to your question.

But, if you’re a seasoned fish keeper who has kept Cardinal tetras for 5 years or more, this might be your answer. Well, cardinal Tetras in captivity live for 5 years.


Old age is inevitable and so is death. The best thing you can do about this is to mourn and provide a good funeral for your Cardinal Tetras.


What Is the Lifespan Of Cardinal Tetra?

Cardinal Tetras live for 5 years in captivity. Due to parasites, predators, and so on, Cardinal Tetras live only a few years in the wild. 

How Do You Save A Dying Cardinal Tetra?

Firstly, add 1 tablespoon of salt per gallon of water. Then, keep your Cardinal Tetra in that salt water for 3 minutes. Remove your fish from the saltwater. After that, transfer your fish to your tank.

This salt bath kills parasites and calms down your Tetra.

Final Words

I hope that among the many reasons I wrote, something clicked with you. Mistakes are common but repeating the same mistake is literally a crime. Especially if it involves your fish buddies. 

By researching more about the problems of your Cardinal Tetra, you can prevent your Cardinal Tetra from dying. 

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