Why did my Goldfish Die?
Reasons and Prevention (2024 Guide)

Lionhead goldfish died due to poor water quality i.e. ammonia poisoning. Dead Small fish on the surface of water.
Dr. Mollie Newton
Published by Dr. Mollie Newton PHD| Senior Editor
Last updated: June 5, 2024
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Regardless of their experience, all fish owners are disheartened by unforeseen fish deaths. Frequently, novice fish enthusiasts question, “Why did my goldfish die?” It becomes particularly frustrating when the causes are unclear, especially when the fish haven’t been with you for an extended period.

Article Summary

  • Common reasons for goldfish dying quickly include uncycled tanks, shock, and poor water quality.
  • Avoid purchasing sick-looking fish or cheap feeder goldfish.
  • To reduce the chances of premature goldfish death, provide them with proper care, including adequate rest, a suitable tank or pond, a clean environment, and a healthy diet.

Knowing the potential cause of your goldfish’s death can help you realize your mistake or error, allowing you to learn from the experience so you know what to do (or what not to do) with your next fish.

Here I’ll be going into some of the most common reasons why goldfish die, as well providing some tips on how to keep your goldfish happy and healthy.

Why Did My Goldfish Pass Away So Quickly?

Goldfish Floating On Top of Fish Bowl
Goldfish Floating On Top of Fish Bowl

There are numerous reasons why goldfish pass away so quickly after being added to a tank, including improper setup, sickness, shock, and poor water quality. Let’s take a closer look into the possible factors of goldfish dying shortly after being brought home.

Uncycled Tank

Perhaps one of the biggest causes of early death in goldfish is ammonia poisoning, often caused in uncycled tanks. Before you add fish to an aquarium, it’s important to cycle it to allow for good bacteria to colonize and prevent toxic water. Look out for symptoms such as black patches on scales, red or bleeding gills, and gasping for air.

You’ll know your tank has successfully completed the nitrogen cycle when ammonia levels and nitrite levels are zero, and your tank is producing nitrates.


Shock in fish can be caused by a few factors, including incorrect acclimation, pH swings (usually as a result of overly large water changes), and drastic changes in temperature.

Goldfish are sensitive to rapid changes in their water, and your aquarium is likely to have different water parameters than that of the water your fish was packaged in.

Acclimating your fish allows them to slowly adjust to the temperature, pH, and hardness of your tank water, which helps prevent shock and stress.

Alternatively, if you perform excessive water changes, the rapid difference in pH and temperature can cause shock in fish, which can be fatal.

Poor Health

Fish can pass away quickly after being added to an aquarium if they were already sick beforehand.

Furthermore, the stress of moving tanks can trigger illness in fish who were in poor health at the pet store.

When choosing goldfish at pet stores, observe the fish closely to spot any signs of sickness or poor health.

Unfortunately, most fish at stores are kept in small living conditions, which can lead to stress and illness.

What to look out for

If any fish in the tank are lethargic, gasping at the surface, lying at the bottom, swimming abnormally, or display other signs of illness like torn fins, mouth rot, fin rot, and ich, try a different store.

If one goldfish is suffering from an illness or disease, the other fish will likely contract it sooner rather than later.

Try to avoid purchasing cheap feeder goldfish too. Feeder fish are sold to be used as food for other animals like reptiles, so they are often in bad shape and poorly cared for.

Why Did My Goldfish Pass Away Overnight?

Fish in Plastic Bags
Fish in Plastic Bags

If your new fish died overnight or a day after you put them into your tank, it’s likely due to one of the reasons above.

However, if you’ve set up your tank properly and acclimated your goldfish but they died during the night, they were likely sick when you purchased them from the pet store.

The shock and stress of moving tanks was probably too much for their body to handle, causing them to pass away.

Do Goldfish Die Easily?

With proper care, goldfish are one of the hardiest species of fish, especially the comet goldfish and common goldfish.

As long as you’ve set up your goldfish tank properly, perform routine maintenance, created an ideal goldfish feeding schedule, and your new fish isn’t showing signs of an existing illness or disease, they’re likely to be with you for many years (often between 10 to 15 years, sometimes more!).

Tank Size

While keeping a goldfish in a bowl isn’t against the law or is an act of animal cruelty, it is still best to give your goldfish enough space for them to be comfortable.

A single common or comet goldfish variety should be kept in at least a 75-gallon tank or pond. Both these goldfish species can grow up to 12 inches long. Ideally, these fish should be housed in spacious outdoor ponds with their own kind.

On the other hand, a single fancy goldfish like the oranda can be kept in a tank size of 20 gallons, adding 10 gallons for each extra goldfish.


The Fluval Accent Aquarium is a good pick for a single oranda as it’s 25 gallons volume. It’s a great starter tank if you’re a beginner fishkeeper as it comes with all the basic necessities.

How Do Goldfish Act When They Are Dying?

Below are some signs that sick fish and dying goldfish can exhibit. If you spot any of these behaviors in your fish, it’s important that you take swift action to identify the underlying cause.

Attempting to Get Out of the Tank

If your fish is attempting to jump out of their tank, it could be due to poor living conditions, such as a dirty environment, overly acidic/alkaline water, temperature drop/rise, pH swing, etc, all of which can be deadly if not swiftly dealt with.

Any one of these issues can lead to fish attempting to escape their tank in search of more favorable conditions. If you spot your fish trying to escape their tank, check your water parameters with an aquarium test kit to make sure everything is in order.

Looks Confused, Disoriented or Swimming Upside Down

Dead Goldfish In Fish Bowl
Dead Goldfish In Fish Bowl

Goldfish who appear confused, disoriented, changing color to white, or begin to swim upside down is a cause for concern. Again, poor water quality or an unsuitable environment may be the cause of aquarium fish displaying these symptoms, or it could be due to illness or disease.

Swim bladder disorders, which are common in goldfish, can cause fish to lose their balance while swimming, resulting in them swimming upside down, on their side, or head/tail down.

Bumping into the Glass or Objects in the Tank

If your new goldfish is bumping into the glass or decor/objects in their tank, they could be dying or be suffering from an illness or disease.

Again, a swim bladder disorder could be at fault.

Issues with your fish’s swim bladder are usually a sign of a larger problem, including constipation, intestinal parasites, being fed poor-quality or incorrect food, and bacterial infections.

Swimming Erratically

If your fish is swimming erratically like continuously darting across the tank or rapidly moving in circles, they may be suffering from an illness/disease like internal parasites or swim bladder disorder.

It could also be due to bad water quality like incorrect pH levels, temperature changes, and high ammonia, nitrite, or nitrate levels. If the problem is not addressed, it can result in your aquarium fish dying.

Swimming to the Surface Appearing to Gasp for Air

Fish lingering at the surface or gasping for air is not a good sign, especially if their gills are inflamed or a reddish/purplish color.

See it in the video below…

Are your fish gasping at the top?

Oxygen deprivation or ammonia poisoning are likely causes, but other factors that can cause breathing problems in fish include gill flukes and sudden changes in temperature.

Why Did My Goldfish Pass Away?

Even the most experienced aquarist is not immune to unexplained fish deaths – it’s, sadly, all part of keeping fish.

When the inevitable happens, it’s important to know how to dispose of dead fish properly.

There have been a few times in my fishkeeping journey where some of my goldfish died suddenly, even when the fish appeared perfectly healthy the day before.

If you’re unsure what caused your fish’s death, here are some possible explanations and causes to help you figure out what may have happened.

Unsuitable Living Conditions or the Wrong Setup

If your goldfish died, especially after only a short time of being with you, it might be due to unsuitable living conditions like the wrong type of water or the incorrect setup. If you didn’t already know, goldfish are freshwater fish, so they cannot survive in saltwater environments.

Learning to build a goldfish tank is your first step towards a long and healthy goldfish lifespan.


Goldfish need to be kept at temperatures between 68 to 74 degrees Fahrenheit. Any hotter or colder than this (especially if the water temperatures rise/decrease too suddenly) can be fatal

Additionally, goldfish are messy fish as they are untidy eaters and produce a lot of waste. So you’ll need a powerful, high-quality filter to match their high bioloads and keep your goldfish alive and healthy.

Tank Size Too Small

An undersized tank can cause a lot of health issues for fish, including stunted growth, weakened muscles, spinal deformities, and other developmental issues. These often lead to a shortened lifespan.

Goldfish forced to live in an overly small tank are also at risk of other illnesses/diseases due to stress.

A stressed fish will have a compromised immune system, opening them up to illness and disease.

Alternatively, if you have too many fish in your tank and have not identified the goldfish sex, it can lead to territorial behaviors and aggression, particularly among male goldfish.


Remember, a single fancy needs a minimum of 20 gallons, while a lone common or comet goldfish needs at least 75 gallons. Add on an extra 10 gallons per additional fancy goldfish and at least an extra 30 gallons for every additional comet/common goldfish.

Incompatible Tankmates

Goldfish in a Tank
Goldfish in a Tank

Housing your goldfish with the wrong tank mates can be disastrous, especially if they are aggressive fish species. Goldfish might be better off alone than live with incompatible tank mates. Goldfish are passive species of fish, so they will be easily targeted by aggressive and semi–aggressive species like bettas, tiger barbs, and African cichlids.

In addition, common plecos and other large pleco species have been known to suck the slime coat on goldfish, the mucus barrier on a fish’s body that helps protect them from bacteria and parasites.

Goldfish Species

Fancy species should also not be housed with common, shubunkin, and comet goldfish as they are slow-moving and less active, causing them to be outcompeted for food or bullied.

The ranchu goldfish is especially slow, so it should only be kept with other slow-moving fish and fancy species.

Avoid small fish as goldfish are greedy and will attempt to eat anything that they can fit in their mouths.


If you want to keep your goldfish in a community tank, small pleco species like the bristlenose and rubbernose often make good tank buddies.

Neglecting Water Maintenance

Failing to keep your tank clean or stay on top of maintenance can cause your pet fish to perish as the water will be full of toxins like ammonia, nitrite, and nitrate. You should aim to remove 20 to 30% of fish tank water each week, replacing it with fresh, dechlorinated tap water.

Chlorine, chloramine, and heavy metals are found in tap water, all of which are toxic to aquatic life. If you don’t add a water conditioner to your tap water to neutralize these pollutants, it can be extremely harmful to your fish and can lead to death.

Substrate Cleaning

Alongside water changes, clean the substrate once a week using a gravel vacuum to remove uneaten food and fish waste, helping prevent ammonia spikes and the development of anaerobic bacteria. Keep an eye out for any dead fish as they will quickly pollute the water and cause an ammonia surge if they are removed quickly.


Check that your aquarium equipment like your heater and filtration system is working properly too, making sure to give both a clean around every 3 to 4 weeks. Only use old tank water when cleaning your aquarium equipment so you don’t kill off any good bacteria.

Poor Water Quality

Water Movement
Water Movement

As mentioned above, neglecting tank maintenance will result in poor water quality, leading to many health issues and, eventually, a dead fish. Ammonia, nitrite, and nitrate will build up if you don’t perform water changes or clean your tank regularly.

Beneficial bacteria is needed to break down organic matter like fish waste and excess food in your aquarium, but if the amount of ammonia and nitrite exceeds that of the good bacteria, it will not be able to convert it quicker enough.

This is common in new tanks that have not undergone the cycling process and dirty aquariums.

Nitrate Levels

High nitrate levels are also harmful to fish. Although less toxic than ammonia and nitrite, nitrate concentrations over 20ppm can have serious consequences. If they are not reduced, fish will begin to display symptoms like rapid gill movement, gasping at the surface, and heavy breathing.

Within a few days to a few weeks, your fish will usually pass away. If your goldfish is subjected to extremely high nitrate levels, they may suddenly die in as little as 24 hours.

Oxygen Deprivation

A lack of oxygen in the water can cause sudden goldfish death. If your fish isn’t getting enough oxygen, they may linger at the surface of the tank, act lethargic, breathe rapidly, or stay close to the filter.

Check that there is water movement at the surface of your tank.

A good-quality aquarium filter will usually create enough surface agitation to encourage gas exchange, but you can also use a bubbler or an air stone alongside a filter to increase oxygen levels in your tank.

Heavy Metals in Tank Water

Chlorine and heavy metals like zinc, magnesium, and cadmium are found in tap water, which is why you should never use it in fish tanks unless it’s been treated with an aquarium dechlorinator beforehand.

Chlorine, chloramine, and heavy metals are poisonous to fish and can lead to sudden death.

Water Parameters

Incorrect or sudden changes to your tank’s water conditions can severely impact your fish’s health and lead to death. This includes keeping your goldfish at the wrong pH, hardness, temperature, or by not letting your first goldfish get used to the water in their new tank properly.

Goldfish do best when their aquarium water has a pH of between 6 to 8 (ideally, around 7.5), with a GH of around 4 to 8 dGH. Investing in an aquarium pH meter would be a good decision as it can be quite useful in monitoring and maintaining the pH levels of your aquarium.

Rapid Water Changes

Performing excessively large water changes, especially in a short period of time, can be one of the reasons why a goldfish dies suddenly. Fish are very sensitive to water chemistry, and any drastic change can result in shock and sudden death.


Additionally, removing too much water at once can eradicate large amounts of beneficial bacteria, causing your tank to re-cycle, even if it’s been established for over a year or more.

Fighting with Other Fish

FISH TANK BRAWL: Aggressive Goldfish

If your fish is attacked by another fish, including another goldfish, they could become critically injured and die as a result. To prevent this scenario from occurring, keep your goldfish in a large enough tank and with compatible tankmates.

Don’t add fish who are aggressive or overly boisterous as goldfish are very peaceful.

Accidents or Injuries

When owning fish, it’s almost certain that one of your fish will get into an accident or injure themselves at some point. This can include a fish tearing their fins/tail against a sharp object, heater burn, jumping out the tank, or getting stuck behind a filter or object.

Choosing Decor

You can decrease the likelihood of your fish injuring themselves by removing sharp decor from the tanks and opting for live plants or silk fake plants instead, as well as using a heater guard and aquarium cover/hood, and ensuring there are no small gaps behind aquarium equipment that your fish can squeeze into.

Illnesses and Diseases

Unfortunately, even healthy fish can get sick from time to time, but feeding your goldfish a good-quality diet and conducting proper maintenance of their tank will help you keep them alive and less likely to contract an illness or disease.

Some common ailments that can affect goldfish include fin/tail rot, ich, hole in the head disease, cottonmouth, swim bladder disease, dropsy, flukes, popeye disease, and fish TB. A fungal or bacterial infection is usually caused by poor water quality, especially if the fish has an open sore or wound.

While prevention is the ideal approach, having knowledge of how to treat common diseases in goldfish, such as ich, can come in handy during an emergency situation.


Make sure you quarantine any new fish or live plants for at least 2 weeks before adding them to your main tank as they could carry an illness or disease that could infect your other fish.


If you’ve had your fish for many years, their cause of death may be age-related. Compared to other fish, goldfish have a pretty long life expectancy when looked after properly, averaging between 10 to 15 years. Some varieties can even live up to 30 years!

Most pet store fish are only a few months old, so provided you give them all the TLC they need, your fish will stay with you for many years to come.

Final Thoughts

Sadly, there’s no way to completely prevent death in goldfish, but you can reduce the chances of it occurring prematurely by giving your goldfish enough time to rest or sleep, a good-sized tank/pond, a clean environment, and a healthy diet. This helps you keep your fish alive and healthy.

Remember, if your goldfish die quickly after you added them to your tank, it may be because it hadn’t finished cycling, you didn’t acclimate your fish properly, or they were already in poor health, such as suffering from a bacterial infection or parasite.

Feel Free To Share!

If you know any other goldfish owners or friends and family in the fish keeping hobby, share this post so they can learn some helpful tips on caring for their pet fish and so they would know the answer to the question, “How did my goldfish die?”.

Take a look at my other guides on aquarium fish and equipment, too, if you get the chance!

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