Why aquarium fish die?

11 Shocking Causes Of Why Aquarium Fish Die Without Specific Reasons

Are your aquarium fish dying? If so, you’re not alone. Every aquarist will eventually face the heartache of losing a beloved pet–it’s an unfortunate part of the hobby. But don’t despair! With some knowledge and detective work, you can figure out why your fish are dying and take steps to avoid further losses.

As an aquarium enthusiast, I’ve seen it all: from nutritional deficiencies to bacterial infections.

In this article, I’ll explain how to identify the cause of death for your fish and suggest ways to prevent future deaths in your tank.

11Shocking Causes Of Why Aquarium Fish Die

Here is a glimpse of the major reasons:

#1 Poor Aquarium Setup

When it comes to aquarium fish health, one of the most important factors is proper setup. Poor aquarium set up can lead to a wide range of issues that ultimately result in dead fish.

For example, the quality of tank water and regular water changes are essential for maintaining healthy conditions and preventing toxic levels of ammonia.

  1. Quality tank water and regular water changes maintain healthy conditions and prevent ammonia toxicity.
  2. Maintain stable temperatures within acceptable ranges to avoid stress and ensure fish survival.
  3. Research temperature preferences of fish species to ensure compatibility.
  4. Install adequate filtration systems for removing harmful bacteria and oxygenating the water.
  5. Improper maintenance techniques can lead to future issues, so be prepared with the necessary tools before adding fish to your tank.

#2 Unsuitable Fish

  1. Ensure fish compatibility and avoid mixing freshwater and saltwater species.
  2. Avoid housing aggressive species together, such as incompatible cichlids.
  3. Overcrowding causes stress due to limited swimming space.
  4. Beware of bad bacteria or parasites introduced to the tank over time.
  5. Provide optimal conditions based on each fish’s needs, including temperature, pH, and quality food.
  6. Understanding and meeting these requirements is crucial for maintaining healthy fish.

Taking these measures will increase their life expectancy and improve their overall well-being during their stay in captivity.

#3 Too Small Tank

Aquariums come in many different shapes and sizes, but the size of your tank can often be a major factor when it comes to why your fish are dying.

If you have a smaller aquarium, even if it is still larger than the recommended minimum for the species or types of fish that you have inside, there could still be too much stress on them from sudden movements or overcrowding. This can cause an unhealthy environment for the plants and other life in the tank as well.

#4 Incompatible Species

It is essential to consider the type of fish you are keeping in your aquarium. Not all types of fish can be kept together and this could lead to serious health issues for your aquatic friends.

An incompatible combination of species will cause stress levels to increase, which leads to unhealthy behaviors such as aggression and dominance. As a result, disease can spread quickly throughout your tank resulting in sick or dying fish. 

#5 Overfeeding

For aquarium owners, it can be tempting to overfeed their fish due to the desire for them to look healthy and happy. However, feeding your fish too much can end up being more harmful than beneficial in the long run.

  1. Uneaten food contributes to ammonia, harmful to fish and tank ecosystem.
  2. Consider the quantity and species of fish when determining food amount.
  3. Avoid overfeeding to prevent food waste and excessive ammonia production.
  4. Proper feeding practices maintain a healthy balance in the aquarium.

The key takeaway here is that an appropriate amount of nutritious quality fish food goes a long way towards keeping our underwater pals safe and sound.

#6 Disease and Parasites

Fish, like humans, are susceptible to diseases and parasites. Healthy fish have a strong immune system and exhibit good scales and skin, capable of fighting diseases and parasites, while stressed fish are prone to illness.

  1. Fish can catch diseases quickly due to stress, even faster than humans.
  2. Continuously monitor your fish and isolate any diseased individuals.
  3. Failing to separate diseased fish can lead to the transmission of diseases to others in the aquarium.
  4. Take proactive measures to maintain the overall health of your fish population.

#7 Lack Of Maintenance

Another common cause for aquarium fish dying is a lack of maintenance. Experienced aquarists know that regular cleaning and water changes are essential to keeping their tank inhabitants healthy and happy, but these same tasks can be intimidating to new or inexperienced aquarists.

  • It’s important to perform regular maintenance on your aquarium in order to keep the environment clean and free from any pollutants that could harm its inhabitants specially a new set-up tank.
  • A newly set-up tank should have an initial partial water change of 25% done immediately after installation, followed by another partial water change every two weeks thereafter with a good quality water conditioner used in each gallon of fresh water added.

#8 Rapid Water Changes

Rapid water changes can be one of the leading causes of pet fish deaths. When aquarium owners are not diligent in monitoring and maintaining healthy ammonia levels, their fish may suffer from poor water quality issues. 

  • Exercise caution with frequent large-scale water changes during regular tank maintenance.
  • Unchecked large-scale water changes can result in an ammonia spike.
  • Test the pH balance, temperature, and water hardness using test strips before adding fresh dechlorinated water.
  • Establish a baseline for these parameters to determine necessary adjustments after making changes to the tank’s chemistry.
  • Proper preparation and monitoring ensure a stable and healthy tank environment for your fish.

#9 Destruction of Beneficial Bacteria

After making a rapid water change, the next step for fish health involves understanding how beneficial bacteria are affected.

  • Beneficial bacteria are vital for maintaining a healthy aquarium and cleaning the environment.
  • Lack of these bacteria can have deadly consequences for tropical fish.
  • Complete the cycling mode process to ensure the activity of beneficial bacteria.
  • Before adding new fish species, use a bacteria starter solution following the product label instructions.
  • This promotes the growth of beneficial bacterial colonies in the tank before introducing Betta or other tropical fish.

Also read: Beyond Goldfish To 10 Best Fish Species For Indian Aquariums

#10 Stressful Transportation

Stress is one of the most essential signs of fish dying. Transporting aquarium fish can be an incredibly stressful experience for the animals. Even when handled with the utmost care, things like temperature changes and water quality fluctuations can take their toll on your fish, leaving them vulnerable to illnesses or even death. Fish keepers must pay close attention to stress levels while transporting their beloved pets if they want to ensure a successful journey.

#11 Other Factors Contributing To Death

Having discussed the stressful transportation of aquarium fish, it is important to consider other factors that can contribute to their deaths.

While many processes and parameters must be carefully monitored in order to ensure fish health, errors can still occur if one or more elements are overlooked.

For instance, loud noises from outside sources such as music or sirens could cause stress for aquarium fish; this means that any tank should ideally be located in a quiet area away from these disturbances.

Additionally, using fresh water instead of tap water with no additives is essential for sustaining healthy levels of nitrate and pH. It is additionally crucial not to overcrowd the tank with too many aquatic animals which will inevitably lead to unstable water conditions and an excess of waste matter such as dead leaves.

Simple Tips On What To Do When A Fish Dies In Your Aquarium?

Witnessing aquarium fish deaths can be devastating. To prevent future losses and maintain a healthy environment, it’s crucial to assess the cause of death. Here are tips for diagnosing the reasons behind the loss:

  • Look for signs of disease or harmful bacteria, such as discolored or swollen skin or gills, rapid breathing, red streaks, and cloudy eyes.
  • Separate any unhealthy fish showing similar symptoms as they may have contracted fatal fish diseases.
  • Quarantine new arrivals to prevent potential illnesses caused by adapting to different water conditions.
  • Check for poor water quality, overfeeding, or a sudden attack if multiple deaths occur within 24 hours. Leftover food can spike ammonia levels, so monitor pH, nitrates, and ammonia regularly, and feed fish in appropriate amounts as instructed on the packaging.

Taking steps like these will help ensure that any future losses can be avoided and your tank remains balanced and happy.


In conclusion, aquarium fish health is largely dependent on the maintenance of their environment.

It’s important to maintain proper water temperature, feed your fish regularly and appropriately, use a suitable filter for your tank, test the water quality regularly, and use an appropriate substrate.

By following these steps, you’ll be able to provide the best possible home for your aquatic friends and help ensure they live long healthy lives. It can be difficult to identify why your aquarium fish are dying without understanding what kind of environment they need to thrive.

The newbies especially lose interest when they witness their fish death primarily due to “new tank syndrome,” which expert aquarists know how to deal with.

If you’re having trouble with this, don’t hesitate to reach out to an aquarium fish health specialist who will be able to offer additional advice.

You can keep your aquarium healthy and happy for years with the right knowledge and care.

Frequently Asked Questions

  1. What is the ideal water temperature for my aquarium?

    A good range is between 72°F and 82°F (22–28°C) for most of the common aquarium fishes.

  2. How often should I feed my fish?

    The general rule for feeding frequency is twice a day, but with moderation – only as much as your fish can consume in two minutes or less. Overfeeding can cause ammonia poisoning, water pollution and health problems.

  3. Does tank size affect fish size?

    Yes, tank size does affect the fish size. Fish will only grow as large as their given space allows them to. If a fish is placed in a mini fish tank, then it will not be able to reach its full-size potential.

  4. What is the best type of filter for my tank?

    We recommend a good hang-on-back or canister filter; these will provide optimal filtration while being relatively easy to maintain.
    When choosing a filter, ensure it has enough power to turn over at least 4 times the amount of water in your tank each hour.

  5. How do I test the water quality in my tank?

    As a fish owner, invest in an aquarium testing kit that can save time and money by providing accurate readings with minimal effort – all you need to do is follow the instructions included.
    You should test your aquarium’s pH, ammonia, nitrate, and nitrite levels at least once a week or more if you’re starting a new tank.

  6. What type of substrate should I use in my tank?

    Gravels are good all-around options, while sand is an excellent choice if you prefer a more natural look. Make sure your chosen product has been thoroughly washed so it won’t cloud your water.

  7. What to do when a fish dies in an aquarium?

    Remove the fish with a small net, change the water, and pour good bacteria as dead fish releases few gases and ammonia in the fish tank. It could be extremely harmful for other fishes to survive.

  8. Should I change the water if a fish dies?

    Yes, you must change the water as the dead fish in the aquarium releases ammonia that contaminates the entire water. After changing the water, it is necessary to check the pH level. This will enable you to ensure that the clean water quality is safe for other fish to survive easily.

  9. How do you know if your fish is stressed?

    When the fish tries to swim back and forth speedily or hides in the bushes, it is an alarming situation that your pet fish is stressed.



Meet me, your dedicated author and fish aficionado. With a deep-rooted passion for all things aquatic, I bring a wealth of knowledge, experience, and enthusiasm to this fish and aquarium website. As an avid fishkeeper myself, I understand the joys and challenges that come with creating a thriving underwater world. Through my articles, guides, and recommendations, I strive to provide you with accurate, reliable, and engaging content that will enhance your fishkeeping journey. Join me as we dive into the fascinating realm of fish and aquariums, and together, let's make your aquatic dreams a reality.

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