Why are my Fish Keep Dying? Top 10 Reasons & Prevention


Why are my Fish Keep Dying?

Managing an aquarium fish tank is fun and rewarding. However, it can be frustrating when the fish die.

You might buy a tank, place it in a perfect place in your home and ensure that the water is running properly. After adding the fish, they start puttering happily around the new home.

It will not look good the next morning when you wake up to find that the fish are dead. It can be sad when the fish die, particularly when you believe that you have done everything in the right way and you do not know what happened.

It is perfectly normal to feel bad, but your goal should be to learn more so that the future fish can be safe. Each time one of your fish dies, you should revisit your tank management.

Today, I have put together the leading causes of fish deaths in an aquarium and the best ways to prevent them.

10 Reasons Aquarium Fish are Dying

So, why are your fish keep dying? Aquarium fish mostly die due to inadequate water and tank conditions. Beside poor water quality they can also suffer from different diseases, stress or it can be a genetic problem that causes fish death.

In the following, I will present you 10 most common reasons why aquarium fish die and will give you some tips on how to prevent fish from dying.

1. Poor Water Quality

Poor water quality in a fish tank is the fastest killer. In fact, the water does not need to be visibly dirty to kill all your fish. Chemicals from the uneaten food and the decomposing fish waste are likely to contaminate the tank and make the water toxic.

Most aquarium fish are known to survive in harsh environments because they have the ability to gulp air from the surface when the water quality is poor and the oxygen level is low.

However, the fish will only survive for a short time. It will take a short time before you start observing the many negative effects of poor water quality in your aquarium tank. Several diseases, such as fin rot, are likely to develop in addition to high-stress levels that can reduce the lifespan of your fish.

To solve the problem, choose a large tank so that your maintenance work can be easier. Use a quality filter and vacuum the gravel during the water changes. Regular water changes will ensure that the living space of your fish is clean.

2. Non-Cycled Tank

A non-cycled aquarium tank is one that is yet to grow good bacteria in the gravel and filter. Addition of fish to a non-cycled tank is not good. Aquarium process is a vital step that beginner level aquarists skip, especially in the form of ammonia.

Fundamentally, fish release wastes continually into the water in smaller amounts. Fortunately, there are bacteria in the water that like ammonia and ready to consume it. That causes another great problem – nitrite. In fact, nitrite is among the most harmful elements to fish.

But just as there are bacteria that love ammonia, there are others that love nitrite. After consuming it, they will output nitrate, which is safe for the fish. The bacteria are easier to grow but their growth may take a long time.

Normally, people cycle their new aquarium tank sans fish but if you already have fish in the tank, you need to approach things in a different way. You will need a test kit to monitor the ammonia level and prevent the death of the fish.

3. Ammonia Poisoning

As I have stated, ammonia is inevitable in uncycled aquarium tanks that contain fish.

The ammonia level might not rise to deadly levels but if you find that the ammonia level is very high – above 1ppm – or the fish are showing any sign of ammonia poisoning such as discolouration, gasping of air, red gills and sluggishness, you will have to take the necessary measures to prevent premature death. Big changes in water are not recommendable because they are likely to stress the aquarium fish.

Change around 50 percent of the water and ensure that the temperature and PH matches, retest the ammonia. 50 percent water change will be enough to reduce the ammonia level. That is all you need to do.

4. Overfeeding

You have to ensure that you are feeding your fish in a healthier way. In other words, you have to provide high-quality pellets, flakes and occasional treats. Unfortunately, some fish owners go overboard and choose to add a lot of food for a single fish to consume in a day.

One cause of illness in fish is overeating. Remember that anything that goes into a fish will definitely come out, which means that the waste in your aquarium tank will be more.

Moreover, the uneaten food will also contribute highly to the amount of waste. Stick to feeding your fish only once in a day because they will eat a lot of food in 1-3 minutes and ensure that you are wasting the least food possible. Consider a fasting day.

5. Overcrowded Fish Tank

If your aquarium tank is very small, it means that the fish will be overcrowded. In fact, that is a death sentence for the fish because of so many reasons. Generally, a small tank will have less good bacteria to break down the waste.

Adding more fish to the aquarium tank will result in more and more poop. If the fish poop more than what the good bacteria can manage to break down, then the water will turn toxic and kill the fish within the process. Most beginners witness this problem, particularly if they have placed their fish in a very small tank.

In addition to overcrowding, a small tank will not provide enough space for your fish to swim. That can cause stress, which is a known cause of premature death. Overcrowding can cause suffocation of fish.

Fish require more oxygen and without it, they will definitely die. Many fish in a small aquarium will breathe faster than the rate of oxygen replacement. That alone will cause suffocation. Remember that your fish can be small today but in a few months, they will have grown.

6. Aggressive Tank Mates

In some situations, your fish will need tank mates. However, when choosing a tank mate, you will have to be careful. Some species of fish might provoke aggression in others. Some are known to mistake others as males or females.

Moreover, there is another good reason to select the tank mates carefully and you might not think of it until it is very late.

Even though some fish are known for fighting and aggression, they might be small and slow moving. The large fish can attack and bully them. The smaller fish might end up nipping at the fins. In other words, the fish will have to deal with long-term stress, which is a known cause of premature death.

After establishing a community aquarium tank, you will need a backup tank to transfer some of your fish if a disaster occurred. It can be a small temporary tank or something similar.

7. Disease or Parasite

Did you know that you are more likely to catch a cold if you are stressed? That is the truth and research has shown that the same is true for fish. Healthy stress-free fish have a stronger immune system. Their scales, skin and the slime coat are capable of resisting any parasite or disease.

Stressed fish, on the other hand, are more prone to diseases and illnesses, which can end up killing them.

Fish are very tiny creatures with primitive brains. They are known to do many unexpected and ridiculous things from time to time.

Sometimes, you will find them sleeping and looking as if they are dead and at other times you will find them spending time on only one part of the tank. That might not be an indication of sickness or parasites.

However, fish get ill like other creatures and stress and dirty water are the two main causes. You will have to familiarize yourself with some common afflictions and diseases like dropsy, ich and fin rot. Ich is a parasitic infection that fish contract from the others.

If you notice any bloating, ragged fins and inflammation of the mouth or gills, tiny white spots, you should know that your aquarium fish have a problem.

8. Water Temperature

Not all fish will do well in unheated aquarium tanks. Some will need low temperatures to survive but others will need temperatures between 75 degrees F and 80 degrees F.

Cool water will mean more stress for some species, illness and even premature death. It can be warm in your place, but temperature drops at night will cool your aquarium tank water rapidly. Choose a large water tank because small amounts of water will cool rapidly.

You can also use a heater. Most importantly, monitor the water temperature to know whether your fish are safe throughout the day.

9. Old Tank Syndrome

Old tank syndrome results from tank conditions that have degraded with time, particularly the chemistry of water. In addition to overgrowth of algae, several other changes might have occurred in the aquarium tank. Phosphates and nitrates are usually high in degraded tan. The water hardness, PH and carbonate hardness will be very different from that of the water you supply.

Typically, PH will become more acidic over time. A falling PH should indicate Old Tank Syndrome. You might assume that everything is right because your fish will be still alive but after adding one or two fish, they will die within a very short time. Some people realize the condition and decide to do a massive cleanup.

The result is usually the death of more fish because they subject the fish to changing water conditions. You have to correct the problem slowly and steadily and never make massive water changes.

Try 10-15 percent of daily water changes to reduce the ammonia and stabilize the PH. To prevent the condition, do weekly water changes and remove debris like excess food particles from the tank bottom soonest.

10. Bad Genetics

At times, you might maintain the needed water conditions and feed the fish appropriately but the fish will be predisposed to diseases. To avoid the death of the fish due to bad genetics, buy them from the reputable and trustworthy breeders solely.

You should not allow a fish with deformities and any of the known issues to breed because it might pass the disease to the offsprings.

How to Keep your Fish Healthy?

Up to this point, I have discussed the potential causes of deaths in aquariums. So, it is time to prevent the unexpected loss of fish in aquariums. Here are the steps to take.

Proper feeding schedule

Overfeeding of fish is a common cause of fish death in aquarium tanks. Unfortunately, most aquarists have the tendency of providing the fish with more and more food throughout the day.

The stomach of your fish will swell if you overfeed them and they do not have the mechanism to realize that they are full and should stop eating. Do not overfeed your ornamental fish regardless of their peculiar characteristics.

If you have been feeding your fish once in a day but providing more than they can consume within 1-3 minutes, then you have been overfeeding them. Fish do not need snacks as you do.

Choose a good time of the day for feeding your fish and stick to it. Remember to teach the other people in your household about the decision and avoid killing your fish with kindness. Feed the fish with vegetables and meaty foods.

Regular tank maintenance

Considerable increase in toxic chemicals is one of the key causes of death of ornamental fish. If you have not set up a robust cleaning cycle of the tank, the introduction of many fish will spoil your tank.

Most of the fish in home aquarium tanks cannot handle instant changes in the water cycle. Some fish are aggressive and might fight with the others in your tank. Fight among the aquarium fish is another known cause of death.

Regular water changes

You will have to change the water in your aquarium tank regularly to prevent the death of your fish. Direct addition of water to the aquarium tank is another common cause of sudden death of fish and you should avoid doing it at all costs.

Buy specific chemicals and use them to remove chloramines from the water. Municipal water departments might add chemicals in the water they supply to kill algae and to prevent scaling in the distribution lines. They do that regularly.

Call the water department to find out the days they add the chemicals. They might have made it a regular practice. That way, you will avoid introducing the chemicals to your tank.

Prevent or combat diseases quickly

Inspect the dead fish carefully and if you see any sign of a disease such as blood under the scales or fins, know that it is a sign of ammonia poisoning or bacterial infection.

If there is anything that is three-dimensional such as white spots, it is a sign of parasites such as anchor worms or ich. White cottony material tufts on the gills, skin or mouth then that is a sign of fungus.

If the fungal infections worsen, they will block the mouth of the fish and prevent them from eating. To prevent death, you will have to do several water changes to remove the swimming parasites and freshen up the water. Treat the symptoms promptly.


After deciding to keep fish, the next thing that you should do is to familiarize yourself with the feeding requirements and the right water conditions maintenance.

Some fish are hardy than others are, but that does not mean that you should not care for them. Feed the fish appropriately and ensure that the water conditions are right to prevent premature death.

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