Why is My Goldfish Dying After a Water Change?

Last Updated on 2023-08-08

Do you change the water in your aquarium, only to have your beloved goldfish die a few days later If so, you may be an aquarist who is at a loss to explain what’s killing them. This is a typical issue among fish hobbyists, so you’re not alone, yet it might be difficult to determine the root cause. But don’t lose hope just yet; we’re here to assist you.

We’ll break down the possible factors at play in your goldfish’s untimely demise, and then provide advice on how to improve future water changes for your fishy pal.

Why Is Your Goldfish Dying After A Water Change?

When it comes to cold-water exotic fish, the goldfish is among the most versatile and aesthetically pleasing tank species you can buy. Unfortunately, there are times when goldfish die shortly after being given a new water supply. This is especially common among inexperienced aquarists who aren’t aware of the importance of taking precautions.

For the most part, while changing the water in a goldfish tank, there are just four potential triggers for dying goldfish:

1.     Temperature Shock

In case you didn’t know, goldfish can survive in a wide range of temperatures. They are able to withstand icy to tropical water temperatures, though not for very long. This is appropriate for a species whose natural habitats feature variable climates and other environmental circumstances. Your goldfish may suffer from temperature shock if the change is too abrupt.

No matter how big or healthy a fish is, it can be killed instantly by an abrupt change in temperature. Fortunately, you can take preventative measures by paying attention to the warning signals of a temperature shock. Among these are:

  • Fish become lethargic in excessively cold water, resulting in slow or non-moving swimming.
  • The increased speed of gill movements indicative of rapid breathing is a telltale sign of the stress caused by warmer-than-usual water temperatures.
  • Your goldfish will die from lack of oxygen since they will constantly try to swim to the surface in heated water.
  • Goldfish swim erratically because the water temperature is too high, eventually wearing them out.
  • A goldfish in a coma will hang upside down and show diminishing vital signs.
  • Death

2.     Extreme Shifts in Water Quality Parameters

In order to keep the equilibrium of an enclosed aquatic ecosystem, water changes are required. The process cleans the air of dangerous substances, reduces the concentration of ammonia, and revitalizes the surrounding area.

Consequences may be severe if water is changed too frequently or in excessive quantities. In particular, the latter.

If your goldfish tank isn’t overcrowded and the water isn’t excessively warm, you shouldn’t need to change more than 10 percent of the water per week.

If you change too much of the aquarium water at once, you risk upsetting the delicate ecosystem that supports your fish.

When the water’s vital minerals, which form a protective layer and sustain the fish, are depleted, this occurs.

In addition to compromising the system’s stability, rapidly replacing the tank’s water can damage the biofilm that has developed on its walls, wiping out cultures of billions of helpful bacteria.

By degrading ammonia and nitrites, these bacteria operate as scavengers and effectively disinfect the system. Many of these cultures will be lost if too much water is displaced, but you might not notice the difference at first. However, without them, ammonia can quickly build up, potentially harming your goldfish.

If your goldfish aren’t overcrowded, you shouldn’t change more than 10 to 15 percent of the water in their tank per week.

3.     Dangers of Excessive Chlorine Exposure

Using municipal water supplies is a common cause of this issue. The chlorine in municipal tap water serves to disinfect it so that it can be safely consumed by humans. To humans, chlorine is completely non-toxic, but it is a deadly poison to the vast majority of aquarium fish. Depending on the concentration of chlorine in the water, the symptoms might be extremely severe.

Some examples of these are:

  • Symptoms of hypoxia appear when your fish are experiencing low oxygen levels.
  • Dead tissue in and around the gills
  • Disordered physical activity caused by neurological dysfunction
  • Rapid death

4.     Poisoning from Ammonia

This is an immediate consequence of a massive water swap. After you’ve finished cycling your aquarium and the system has stabilized, you should focus on maintaining that stability. It’s important to keep the tank’s environment stable by preventing drastic water changes that could wash away the cultures of helpful bacteria. These are what break down ammonia and nitrites into nitrates, which are safer for your goldfish, as previously discussed.

Ammonia levels will rise quickly without them, especially in a goldfish tank, because these fish are so filthy. The symptoms of excessive ammonia accumulation are context-specific and might change as the concentration of ammonia rises. At first, your goldfish may show signs of ammonia stress, including:

  • Struggling for breath
  • Hunting for a place to hide
  • Increasing hostility toward one’s tank mates
  • Displaying puffy eyes and an irritated anus
  • Notable sluggishness and lack of enthusiasm
  • Appetite suppression or loss

Ammonia poisoning, if present, will cause more severe symptoms in the fish. Among these are:

  • Changes in the color of the gills from red to blood red
  • Inability or refusal to consume food
  • Reddened, blemished, or otherwise broken skin all over
  • Inactivity on par with a coma
  • Inconsistent Strokes
  • Fins fastened together, lying on the tank floor
  • Bleeding both internally and externally
  • Death

How To Save A Dying Goldfish After A Water Change

Acting quickly and decisively is the only way to save the goldfish from imminent death. Here are a few things you need to do:

Do Not Feed

If the temperature in your fish tank suddenly drops or rises by a large amount, the fish may not be able to digest any food at all. This is more likely to happen if the water temperature drops below the fish’s metabolic threshold. Reduced digestive efficiency can lead to gas, constipation, and even compaction in the fish. Compaction is

a severe case of constipation in which the fish’s intestine stops producing mucus, causing waste to become trapped and dry out. Since it can cause so many other problems, compaction is typically fatal.

The second issue is that the shock may prevent the fish from eating. So, if you throw food into the tank, it will eventually sink to the bottom and rot. Ammonia levels will rise much higher, wreaking havoc on the ecosystem and making matters worse.

Let the fish rest and go back to normal by fasting for a few hours.

Aerate the Water

Aeration is not the same as oxygenation.

Dissolved oxygen is what we mean when we talk about oxygenation. However, aeration necessitates both the introduction of oxygen and the movement of water. To promote aeration, then, you must do two things: increase the water’s flow rate and increase the oxygen content.

Having a pump on hand makes aeration a breeze. You need merely adjust the pump’s settings to achieve the desired output. Additionally, you should increase the tank’s surface area, use waterfall filters, and add more plants. The water in the tank will be exposed to more air if you do this.

The comfort of your fish will greatly increase if you increase the aeration and oxygenation of the water soon after doing a water change.

Implement the Use of Chemicals

You should apply a water conditioner if you think a chemical imbalance is to blame for your fish’s death. These items are fantastic because they filter out harmful toxins, help fish heal, and shield them from the environment. Please use these conditions in accordance with the published guidelines. Seek the advice of an expert if you are unsure of how to carry it out.

Use Salt for Aquariums

When it comes to ill goldfish, aquarium salt is like a shot of adrenaline, especially for those who are experiencing issues due to water changes. Aquarium salt has many beneficial uses, including accelerating tissue repair, enhancing gill function, facilitating respiration, and supplying electrolytes that are lacking in tap water. Even though it has nothing to do with the subject at hand, it’s important to know that aquarium salt is effective against parasites, viruses, fungi, and bacteria.

To kill these bacteria, salt must dehydrate them, and it can do so at amounts that won’t harm the fish. This may be important to know if your fish develops secondary illnesses after suffering tissue damage from ammonia.

Utilize a Carbon Filter

When keeping numerous fish in a larger tank, a carbon filter is a must. Carbon filtration guarantees that harmful substances like chloramine, chlorine, ammonia, and other contaminants and organic and inorganic residues are removed from the water.

Following a systemic treatment, activated carbon can be used to remove any leftover drugs or antibiotics from the tank water. Plus, it gets rid of the smells that develop in an aquarium over time, especially if the tank hasn’t been well maintained.

In the event your fish exhibits signs of extreme stress or shock after a water change, you can utilize the procedures described above to treat them effectively.

betta care facebook group

Why Is Your Goldfish At The Bottom Of The Tank After The Water Changes?

Are you an aquarist who’s been wondering why your goldfish tends to sink to the bottom of the tank after water changes? It can be a mystery, but with a little bit of knowledge and proper maintenance routine, you can protect your goldfish from this common behavior. Read on as we discuss what could be causing this issue, how it affects the health of your fish, and tips on how you can keep it from happening.

Sudden Decrease in Oxygen Levels

Goldfish are sensitive creatures, and when there’s not enough oxygen in their environment. When there is insufficient aeration or filtration, the water quality will quickly become depleted of oxygen which can be harmful for your fish.  They become stressed and start to sink as a natural reaction. This happens because the fish’s gills aren’t able to extract enough oxygen from the water, leading it to become lethargic and lose control of its buoyancy.

Sudden Change in Water Chemistry

Water changes can result in significant fluctuations in pH, ammonia levels, nitrite levels and other parameters. Goldfish are highly sensitive to these changes and may struggle to adjust their internal physiology quickly enough. If the fish has been exposed to conditions too different from what it is accustomed to, it may feel stressed and sink to the bottom of the tank.

Sudden Drop in Water Temperature

Goldfish are extremely sensitive to sudden changes in temperature and may become lethargic if the water gets too cold or hot. If you recently changed the tank’s temperature, your goldfish may have been affected by it and may be sitting at the bottom of the tank as a result.


Another potential reason why your goldfish may be sitting at the bottom of the tank after water changes could be stress. Goldfish can become stressed from sudden changes to their environment, such as water chemistry shifts. Whenever there is a change in the environment, it can cause fish to become stressed out which can lead to them hiding and seeking shelter at the bottom of the tank.

Now that you know the possible causes of why your goldfish is sinking after water changes, it’s time to take action. To prevent this issue from occurring again:

  • Make sure you maintain a good maintenance routine to keep your tank clean and oxygen levels high.
  • Perform regular partial water changes and use a dechlorinator for each change.
  • Test your tank’s water parameters regularly and monitor the levels of ammonia, nitrite, and nitrate.
  • To reduce stress levels, make sure that you are providing plenty of hiding spots and reduce noise and activity levels in the tank.
  • Finally, make sure you keep your filter clean to avoid any buildup of waste in the tank.

With these simple yet effective steps, your goldfish will stay healthy and happy in its aquarium environment!


How Sensitive Are Goldfish to Water Changes?

Water changes don’t seem to affect goldfish too much, however it depends on how you go about doing them. Ten percent to fifteen percent water changes every week is the sweet spot. While this is sufficient to improve the goldfish’s surroundings, it is insufficient to significantly alter the water’s chemistry.

Can a Goldfish Survive in Fresh Tap Water?

Goldfish can only survive in tap water that has been properly treated to remove potentially harmful chemicals. The chemicals in tap water will kill all of the “good bacteria” in your tank.


Water changes are a necessary part of keeping your goldfish healthy and happy, but sometimes they can be stressful for your fish. Be sure to acclimate your fish slowly to any new water conditions, whether it be temperature or chemical makeup, and pay close attention to them after the change. If you notice any changes in their behavior or appearance, act quickly to save them. With a little bit of care and attention, you can keep your goldfish happy and healthy for years to come.

Ultimate Betta Fish Care Guide
About the author

Hey! I'm Nicolas from Iguane Media !

Blogger and Owner of the betta care fish guide
Thanks for reading this blog

I'm an Animal Lover

Leave a Comment


Enjoy this blog? Please spread the word :)