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Why Are My Goldfish Dying? Common Causes & Solutions

Goldfish are relatively hardy fish, but as I’ve found out over the years, unfortunately, there are some things that can kill them. If you wonder: why is my goldfish dying? here’s the answer:

Quick Answer

Some of the most common causes of goldfish dying include poor water quality, overcrowding the tank, inadequate filtration, improper feeding, temperature fluctuations, incompatible tank mates, general stress, and all sorts of diseases.

Keep reading to find out what all of the most common causes of goldfish death are, and what you can do to prevent them from occurring.

Main Reasons Why Goldfish Die in an Aquarium

There are several reasons why your goldfish could die. Let’s go over them one by one.

1. Age

A goldfish that is well cared for may live for around 10 or 15 years at the very most. Therefore, if you’ve had a goldfish for many years, and it starts slowing down or it dies, chances are that it was due to nothing more than old age. Goldfish don’t last forever. Of course, there is no solution to this problem at all.

two goldfish in aquarium with green plants in the background

2. Poor Water Filtration and Bad Water Quality

One of the most common causes of goldfish death, besides old age, is poor water filtration which results in bad water quality. 

The simple fact of the matter is that you need to have a good water filtration system for your aquarium, or else your fish will not survive.

You need to have a filter that engages in all three major types of water filtration, which include mechanical filtration, biological, and chemical filtration.

Mechanical filtration is designed to remove all sorts of solid waste such as fish waste and uneaten food from the water. Biological filtration is designed to remove ammonia, nitrites, and other substances from the water. 

Chemical filtration is designed to remove toxic substances such as heavy metals, chlorine, as well as odors and colors.

Now, there are plenty of substances that can build up in the water when there is a lack of adequate filtration. One of the most common and problematic ones is ammonia, which is released by fish food and fish waste, as well as dying plant matter. Ammonia spikes can very quickly kill your fish, essentially burning them from the inside out.

The best solution to this problem is to upgrade your filtration unit so that it performs all three major types of water filtration adequately. Your filter should be able to process at least three times the total water volume in the tank every single hour. 

If your filter is working properly, you’re definitely on the right track, although there are also other factors that can cause poor water quality, such as overcrowding, which we will discuss further below.

However, as far as poor water quality is concerned, an immediate solution is to perform a water change of up to 50%. Keep in mind that generally speaking, you only want to perform water changes of 30% at a time, and only up to once per week. 

Changing any more of the water can also cause issues, mainly in relation to biological filtration and beneficial bacteria that are removed from the tank with every water change. However, if you think that there is a big ammonia spike, doing a big water change will take care of this problem.

3. Overcrowding

Although many people may not see overcrowding as a leading cause of goldfish death, the simple fact of the matter is that a crowded environment causes many problems. 

First and foremost, the more fish you have in a single tank, especially in a small space, the more waste they will produce and the more uneaten fish food they will leave behind.

Simply put, the higher the concentration of fish in a smaller space, the dirtier the water is bound to be. This means that your filter needs to work overtime to keep the water clean. This may also lead to a spike in ammonia and other contaminants in the water which can be harmful to your fish.

At the very least, if your fish are overcrowded, they may become extremely stressed out. Stressed out fish become much more susceptible to disease, something we will discuss further below. Stress itself can in some cases kill fish, and if it’s not the stress, then it will likely be disease.

4. Temperature Issues

Yet another big cause of goldfish death are temperature fluctuations. Remember that goldfish are cold water fish and they are quite sensitive to temperature fluctuations. 

Generally speaking, the ideal temperature for goldfish is between 65 degrees and 75 degrees Fahrenheit, with somewhere around 70 degrees being best.

Now, goldfish can survive in a wide temperature range, as low as 55 degrees and as high as 80 degrees, so it’s not as much the temperature that is the issue as much as the temperature fluctuations. 

If the temperature constantly changes, it will stress out your goldfish and cause health issues.

Temperature fluctuations may cause cold stress or heat stress, which can make them more susceptible to disease and death. Worst case scenario, extreme temperature fluctuations can cause heat stroke or quite literally cause your goldfish to develop hypothermia and freeze.

The simple solution here is to get yourself an aquarium thermometer so you can constantly monitor the temperature inside of the tank and make adjustments as necessary. 

Want to learn more? Check out our guide on the ideal temperature for goldfish now!

5. Improper Feeding Practices

The next common cause of goldfish death is improper feeding. If you don’t feed your goldfish the right types of food, it can lead to a variety of digestive issues. Remember that goldfish need to have a whole lot of protein in their diet, and if they don’t get it, it will cause problems.

Not eating your goldfish the proper diet can cause high levels of stress, therefore making your fish much more susceptible to a variety of diseases. 

Improper feeding practices, especially if the wrong food is concerned, may also cause a few such as compaction, bloat, and more. Furthermore, maintaining a good feeding schedule is also important.

Both overfeeding and underfeeding your goldfish can also cause serious health issues that can lead to death, even in the short term. Make sure that you feed your goldfish only twice per day, and only as much food as they can eat in two or three minutes at the most. 

Using high quality fish flakes and fish pellets is also recommended.

6. Incompatibility with Tank Mates

Although this cause of goldfish death is not quite as common as some of the others that we have talked about so far today, the fact of the matter is that there are times when tank mates can cause problems for your goldfish.

Sometimes, if you get much larger tank mates, they may bully or even kill your goldfish outright. At the very least, bigger and faster fish may end up eating all of the food meant for your goldfish, which essentially causes your goldfish to starve.

Therefore, before you get any kind of new page to put in your goldfish tank, make sure that the two are compatible and that they will not bully or try to kill each other. 

Remember that there are also types of fish known as fin nippers, which may nip at the fins of your goldfish, which in itself can also cause serious problems.

7. Handling Stress

The unfortunate reality is that in the grand scheme of things, goldfish are still relatively fragile, as are most fish. The simple stress created by transporting them, such as from the pet store to your home, can in some cases be enough to kill them.

Unfortunately, there is not all that you can do to mitigate this problem. Sure, you can transport them using the proper equipment and you can make sure to take things nice and slowly, but inevitably, some fish will die as a result of being handled and transported.

8. Chemical Contaminants in the Water

Although also not quite as common a cause of goldfish death as some of the others on the list today, there are still some chemicals, medications, and other toxic substances that may be present in the water which can be harmful to your fish.

One of the biggest ones are a variety of heavy metals, something that you can effectively remove from the water with some regular chemical filtration. Always make sure that you are using clean water that has been tested and treated for any such substances if necessary.

Another important thing is that your tap water needs to be suitable for goldfish. More on whether goldfish can live in tap water can be found here.

9. Disease

There are then many other causes of goldfish death which can all be put into one category, disease. Unfortunately, there are a variety of diseases that can affect your goldfish, so let’s take a quick look at each of them.

A. Ich

Ich is a disease characterized by white spots or cysts on the skin, gills, and fins of the fish. You may notice your goldfish rubbing against objects.

If your goldfish has ich, the treatment is to raise the water temperature slightly, up to 80 degrees Fahrenheit over the course of the several days, and to use a proper treatment for the disease that contains copper or formalin. You also need to quarantine the affected fish.

B. Fin Rot

If you notice that your fish has ragged, torn, and decaying fins which are also discolored, then it is likely that your fish is suffering from fin rot, something which can rather quickly lead to death.

There are antibiotics designed specifically to treat this issue, with the other solution being to do rapid water changes to quickly improve the water quality. Getting a better filtration system is also an option.

C. Dropsy

Yet another common cause of goldfish death as far as disease is concerned is known as dropsy. Dropsy is a disease characterized by scales sticking out of the skin like pinecones, a swollen abdomen, loss of appetite, and lethargy.

To treat dropsy, make sure to isolate the infected fish so it does not spread. Furthermore, you then need to maintain stable water temperatures, improve the water quality, and there are also antibiotic treatments. 

Unfortunately, dropsy is one of the harder issues to deal with, and even with proper treatment may still result in death.

D. Velvet Disease

Velvet disease is characterized by a rust-colored film on the fish’s skin, flashing, and rapid gill movement. To take care of this issue, you need to increase the water temperature to roughly 80 degrees Fahrenheit and treat it with a medication that is copper based, which is designed to treat parasitic infections.

E. Bacterial Infections

There are a wide variety of bacterial infections that may also affect your goldfish. Some of the most common symptoms include ulcers, frayed fins, red sores, lethargy, and a lack of appetite.

If you think that your fish might have a bacterial infection, you need to isolate infected fish and treat them using a broad-spectrum antibiotic design specifically for fish. 

Also make sure to perform regular water changes and to ensure that the water quality is quite high in general.

F. Anchor Worms

Yet another issue that your fish may be faced with are known as anchor worms. Here, you will see small greenish or white worms that protrude from the skin of your fish.

To take care of this issue, use some tweezers and a cotton swab dipped in hydrogen peroxide to physically remove the worms. There are then also a variety of medications that you can use to treat external parasites in fish.


I know that this sounds like a super intimidating list of all of the different things that can kill your goldfish.

However, the reality is that in my best estimate, upwards of 75% of goldfish deaths are a result of improper handling, poor water quality, inadequate filtration, and issues that generally come back to a lack of proper care.

Therefore, if you feed your goldfish a proper diet, maintain good water quality, give them good filtration, and handle them with care, you should be able to prevent any such causes of death.

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