Why Your Fish Keep Dying? 14 Causes & How to Stop it

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Why do my fish keep dying?

This is one of those dreaded questions beginner hobbyists fear asking. It is a sign of several things going wrong, mainly due to a lack of experience in the field. But do not worry, we have all been worried like you, and we figured out the answers.

If your fish constantly die, you should not fret since most causes are easily preventable. Stress is the number one cause for constantly dying fish, subsequently caused by many reasons related to water quality, unsuitable water parameters, poor aquarium ecosystem, poor fish acclimation, and aggression from other fish, to mention a few.

why do my fish keep dying

If the fish keep dying, but the water is fine, this points to illnesses, old age, poor feeding habits, poor tank conditions, toxins from external sources, and prior problems with the fish.

Read on to learn the top causes of this issue and how you can easily prevent it with several precautions.

Most Common Causes of Your Aquarium Fish Dying

1. Poor Water Quality and Unsuitable Water Parameters

The water is the most important aspect of your hobbyist journey. This ranges from the quality of the water to the water parameters, including the pH levels, temperature of the water, nitrogen/ammonia concentration, and salinity.

Poor water conditions are the number one reason why your fish keep dying suddenly. It indicates that the environment is so severe that the fish cannot last long. As an aquarist, the condition of your water should be your highest priority.

A testing kit is a vital tool for this case. Take readings regularly and ensure you notice any water parameter changes at any time. Different fish require different water conditions; check with your supplier and the internet on the most suitable conditions for your species.

The important part is to keep the parameters stable. A perfect reading is great, but you will only benefit from it sometimes. Clearwater is only sometimes the best, but stable parameters are.

A common problem in aquariums is ammonia level spikes (acceptable ammonia levels are zero). Ammonia increases due to lots of uneaten food, dead plants in the tank, dirty filter pads, and decaying algae.

Poor Water Quality and Unsuitable Water Parameters

These lead to the burning of gills at low levels and eventually brain & organ damage till the fish eventually dies. You can prevent ammonia and other dangerous parameter spikes by performing regular maintenance, keeping a healthy number of bacteria, avoiding overfeeding, and keeping the appropriate number of fish in your tank.

Also, ensure you get rid of any dead decomposing aquatic life in the water: from fish to snails, plants, and other dead living organisms. Decomposing aquatic life can lead to ammonia spikes in the tank.

2. Poor Tank Conditions

‘New Tank Syndrome’ is a common issue among first-timers. It refers to a set of unlivable conditions caused by the accumulation of toxic compounds, resulting in the contamination of fish in a new aquarium. Good bacteria are beneficial in processing the fish’s waste, but it takes time to build up about two months.

It is advisable to cycle your aquarium and introduce friendly bacteria before adding in the first fish. It would be best if you also started with persistent species that can survive longer in such conditions to build a friendlier ecosystem. Add more fish afterward.

Also, the number of fish in your tank can make the aquarium unlivable and cause the fish to die. One small fish per gallon of water is the recommended starting point for newbies; later on, the mature aquarium can fit two of them per gallon of water.

Did you know the aquarium light is only for you to see your fish? The aquarium fish only need light to know its day or night, but a naturally well-lit room is more than sufficient to do the job.

You should keep your aquarium lights on for 8 hours or less. This is because too much of it can cause algae to grow faster. It can also promote attacks from aggressive fish and obstruct the hiding spots of certain fish that like to isolate themselves, hence raising the fish’s stress levels.

You will need some extra equipment to make your aquarium more sustainable. A wave maker is one example that helps oxygenate the water through surface agitation.

It would help if you also considered getting backup air in case of power failure that may cause your fish to die overnight during a blackout. A functional heater system is great for ensuring the temperatures are optimal.

3. No Fish Acclimation

Why did your fish die when you put them in a new tank? Fish dying in a new tank is a clear indicator of poor fish acclimation (and sometimes poor tank conditions), especially when the fish die immediately after you place them in a new tank.

It is vital to ensure you do not induce shock on the fish when you introduce them to new water conditions. This is done by a process called fish acclimation. It applies to new fish coming into your mature tank, new fish in a new tank, or introducing fish back into the tank after some maintenance.

There are several ways of acclimation, but the main principle is to gradually introduce/reintroduce the fish into the water conditions in your tank. Shock can happen when the temperature is not the same as the one the fish is used to.

Other water parameters such as pH, salinity, nitrates, and magnesium levels are also important. Follow a quick guide to acclimation to avoid shocking the fish, which can lead to death.

Also Read: How To Acclimate Fish

4. Low Maintenance

Performing maintenance on the aquarium can seem like a daunting task, but you will be surprised at how easy it can be. About 30 minutes a week is what you need to prevent common problems and illnesses befalling your fish. Start with checking the vital water parameters to ensure they are optimal.

The most important aspect of the maintenance is changing about 10 – 15% of the water in two weeks, followed by vacuuming the gravel to get rid of waste, accumulated food, and toxic compounds on the tank floor.

Remember to get rid of chlorine when adding new water. Tap water usually has chlorine, which affects the fish by damaging their gills and making it hard for them to breathe. Tap water also kills natural bacteria. Dechlorinate new water by neutralizing the chlorine or using a water conditioner.

The filter is another crucial part of the tank that needs to be serviced at least once every month. The filters are where all the dirt and trash accumulate. It is important to get rid of this waste to avoid contamination.

Empty the filter and only use tank water/fresh water to clean it to avoid disrupting any friendly bacteria on the device. Detergents and other cleaning chemicals kill good bacteria.

When performing maintenance, ensure to alternate between water changes and filter cleaning. Performing these two tasks together will disrupt ammonia concentration.

Long-term maintenance ranges from keeping the heater in optimal condition and ensuring the filter works properly.

Low maintenance leads to poor living conditions that create a toxic accumulation of waste, algae, and uneaten food that kills fish. Cloudy water is a clear sign that you have been far behind your required maintenance hours.

Also Read: 14 Best Algae Eaters

5. Wrong Fish Ecosystem

The species in your tank are very important. Some fish do not coexist well with other species. Please ensure you have a habitable environment for your different breeds in a harmonious and non-aggressive environment.

6. Illnesses

All animals are subject to diseases, attacks from parasites, and dangerous bacteria. Brace yourself if you are a new hobbyist because diseases will attack your fish sooner or later, and it is always good to prepare yourself.

The good news is that healthy fish living in a healthy environment will fight the most common diseases. However, if the habitat isn’t well maintained, the chances of the fish contracting something deadly go higher.

A common issue that leads to illnesses is ammonia poisoning. Symptoms on the fish include but are not limited to purple/red gills and fish that swim on the surface to get fresh air.

A similar condition is nitrite poisoning, characterized by the same gasping for air and brown/tan gills. You can prevent this by a 50% water change and neutralizing the ammonia/nitrite levels to zero.

Bad bacteria cause fins to rot, but a full tank cleanout can rectify it. Take a look at a comprehensive fish disease guide to know all the precautions you can take to prevent your fish from dying.

Related: How to Save Dying Fish After Water Change

7. No Quarantine

Quarantine is something many people skip over. It is rarely a cause for concern, especially when getting new fish from the same source as the prior ones. Quarantining new fish is important when introducing them to an aquarium holding other fish for months or even years.

The animals get so comfortable in their habitats that it becomes hard to fight new diseases and contaminants. If the new fish has some pathogens, it can quickly attack the older fish and kill them.

To quarantine, you must place the new fish in a similar tank with a similar habitat for about 2 to 4 weeks. Attend to both tanks as normal; once time passes, you can put the two stocks in one main tank.

8. Old Age

The saddest of realities also faces fish just like it faces human beings; old age leads to death. The life expectancy of fish varies across species. Your fish may frequently die because they come from an old fish stock or are aging after being owned by a previous hobbyist.

Take heed of aging fish signs like its stated life expectancy, weight loss, skin discoloration, poor eating patterns, breathing problems, and the fish floating on its side.

Old age can also cause death without prior signs due to their unique evolution properties that hide their age and only present themselves in slight environmental changes.

9. Poor Feeding Habits

Poor feeding habits are common causes of fish dying when you are starting on your fish-keeping journey. Many newbies tend to overfeed their fish.

This leads to a lot of fish waste production and accumulation of uneaten food in the tank that is toxic to the habitat. Improper digestion is another concern that can lead to fatty liver disease in fish.

Feed your fish with the recommended portions. You can gradually increase or reduce the amount of food by monitoring what goes uneaten in about five minutes. This will help you know what portions the fish need to sustain themselves and how you can set a stable, healthy feeding schedule.

Always remove uneaten food from the tank with a net.

10. Toxins from External Sources

It is unsafe to clean or touch the water in the aquarium with unclean hands. External elements can be toxic, including perfume, hand lotion, or any cleaning chemicals used to remove waste and perform maintenance.

11. No Lids

Aquarium tank lids are vital for keeping external toxins from entering the habitat. Simple elements like the chemicals from a bug spray or a whiff from your elegant perfume can sip into the water and alter the water quality/parameters.

12. Agitation During Transport and Certain Movement

Transportation from the pet store to your aquarium at home can be a hassle for you and the fish. A sudden movement in the bag, water conditions of the transportation container, and traveling conditions can stress and shock the fish to death.

It would help if you noted any agitation and sudden movement while performing regular maintenance.

13. Stress

As we can tell, all the above conditions lead to a lot of stress on the fish. Fish are very sensitive to unstable water quality and water parameters. Spikes in pH levels, temperature, ammonia, and magnesium can agitate the fish easily, leaving it vulnerable to ailments and more attacks.

Stress can show itself in a fish from how it eats and if the fish gets sick often due to a weakened immune system.

Bullying from other fish is also a major contributor to the stress leading the fish to hide most of the time and eat irregularly.

14. Prior Problems with The Fish

If you have gone through all the causes above, you may still wonder why your fish keeps dying after ticking all the boxes. It is frustrating, I know.

But this is where we let you know that some causes are out of a hobbyist’s control.

The fish may have congenital issues that make it harder to survive in any environment. You may also have obtained the fish from a bad stock, especially if you bought it from an inexperienced/less-cautious supplier in a small shop. Or maybe the fish was unhealthy, to begin with.

It is sad, but such is the nature of keeping fish. Sticking to experienced huge online and physical shops is a good start. You can also look for any signs of illnesses in the fish you want to get or stick to young, healthy breeds.

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Final Thoughts

Most fish die because of human error. It is natural for human beings to make mistakes. Your fish may be dying because you forgot to keep up with the proper maintenance schedule, overfed them, or failed to turn on the filters or lights after your frequent maintenance.

This is more common for beginners but also happens to expert aquarists. Do not fret; it happens, and you will get the hang of it. Take it easy; we have all made these mistakes and learned from them, and you will too.

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2 thoughts on “Why Your Fish Keep Dying? 14 Causes & How to Stop it”

  1. This is very helpful thank you for writing this I recently got fish and I am a newbie and all died in a week. I feel terrible but I will take the advice I read here and apply it for future set ups.

    I am gonna let my tank run for a few weeks with no fish or simple ones like goldfish or guppies.

  2. I left my fish tank in care of someone else while on vacation,and all my fish died. It was a well contained tank. Although I’m not sure what the person did. This reading was very helpful. Thank you.


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