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Goldfish suddenly die: common causes

If goldfish suddenly die in the pond or aquarium, the causes must be found urgently so that, ideally, remaining stocks can still be saved. The most common causes can be found below.


Water temperature

If the temperature in the pond or aquarium rises sharply, the oxygen uptake of the water deteriorates. This can lead to a serious lack of oxygen from which goldfish can die from suffocation within a few hours. The control of the water temperature is especially necessary during hot summer days. The following aspects must be taken into account:

  • Goldfish can tolerate water temperatures between four degrees Celsius and 30 degrees Celsius
  • permanent temperature not exceeding 20 degrees Celsius
  • correct immediately if the water temperature is suboptimal
  • Make the water circulate to promote oxygenation


If the goldfish suddenly die, it may be due to poisoning. This is mostly due to care errors or insufficient water purification. However, too high a fish population in a body of water that is too small can cause values ​​that are too high, which most frequently affect nitrite, ammonium and ammonia.

  • Control of values
  • Risk of poisoning with nitrate levels of over 30 milligrams per liter
  • Ammonium and ammonia are created when the pH value is too high, above 7.0
  • if limit values ​​are exceeded, filter the water immediately
  • Ideal case: move goldfish temporarily into fresh water until the pond / aquarium has been filtered or the water has been changed
  • Use an oxygen or circulation pump to stimulate oxygen
  • Regularly clean water as a preventive measure, test the water quality and optimize it if necessary
  • reduce fish stocks if necessary - guideline value: two goldfish per cubic meter of water


Goldfish do not have a feeling of satiety and can overeat if they are fed too much too often, but they do not die in large numbers and suddenly. The cause is leftover fish food, which causes the water quality to tilt at the bottom when it rots. Then the same thing happens as already described under “Cause poisoning” and the countermeasures look the same.


Also due to poor water quality, ascites is often the cause of the sudden death of the fish. This sets in motion a life-threatening bacterial infection. They show special features that indicate the disease. Without correcting the cause and treating them, they die relatively quickly. If suitable measures are taken early, the chances of survival for the remainder are good.

Recognize ascites

  • stay in a pond / aquarium corner
  • hardly swim
  • have a clearly bloated belly
  • protruding scales
  • possible imbalance disturbances with the impression of disorientation
  • Eyes may protrude puffy


  • Check the water quality immediately and correct the values
  • Administer a broad spectrum antibiotic (active ingredient nifurpirinol is recommended by many experts - 1 tablet per 25 liters)
  • Check fish stocks and reduce them if necessary - ideal: two goldfish per cubic meter of water
  • Thoroughly aerate the water during the treatment and filter it continuously
  • Activated carbon cleaning is ideal - it reliably removes drug residues from the water
  • make sure to clean the floor

Copper wires

One of the most common causes of sudden death for goldfish is old copper pipes that allow water to enter the pond / aquarium. If the copper content in the water increases, poisoning of the entire fish population is possible within a few hours. The copper content can usually be seen just by looking, because the water is slightly rusty in color. It often smells metallic too. This is how further fish deaths can be countered:

  • With all available filter pumps, the water can also be cleaned at full speed
  • Alternative: remove the fish immediately, put them in fresh water with an oxygen pump and empty the pond / aquarium
  • Thoroughly clean the pond / aquarium
  • ensure sufficient oxygen before fish can return to freshly filled water
  • Giving a fish mineral promotes vitality and promotes detoxification
Tip: Not every goldfish owner can replace copper water pipes. Here it is important that another source of water is used for the filling or that the copper-containing water is at least treated beforehand with suitable additives that neutralize the copper content. BioTeich Vital is just one example of a suitable product.

White spot disease (Ichthyo)

White spot disease is widespread worldwide and is caused by parasite infestation in the so-called ciliates. They get into the water either through infected newcomers or the addition of (used) stones / decorative elements with parasite infestation. There they spread rapidly and mainly attack stressed goldfish and / or with a weakened immune system. With immediate discovery and correct treatment, the goldfish dying can be put to an end relatively quickly. However, very weak animals have little chance of survival because it takes a little time before treatment is effective. Dying within a few hours is possible.

Recognize white spot disease

  • white spots on fins (initial stage)
  • in the later stage distributed over the whole body
  • Unwillingness to eat
  • pinching the fin
  • infested goldfish separate from the group
  • slimy, inflamed skin
  • itch on objects, because sometimes severe itching, depending on the degree of inflammation of the skin


  • First aid: Increase the water temperature briefly to 30 degrees Celsius (maximum two to three days) - kills numerous parasites
  • If the water temperature is higher, it is essential to connect the oxygen pump continuously
  • Alternative: relocate diseased goldfish into fresh water every twelve hours for seven days
  • most effective: administration of malachite green, for example (treatment duration approx. 20 days)
  • Thorough cleaning of stones and decorative elements (vinegar helps against parasites - but has to be washed off meticulously before going back into the water, as vinegar negatively changes the pH value)


Columnaris is a bacterial infection that is the most common cause of sudden death in goldfish, just behind white point disease. The infection can spread rapidly to other conspecifics and in this way kill large groups of goldfish and other fish species within a very short time. The disease usually occurs in aquariums. The infection cannot be clearly distinguished from all bacterial diseases. These bacteria often form in wounds after fights for hierarchy with other fish or are introduced by newcomers.

Typical characteristics

  • Fin clamps
  • rocking movements when swimming
  • apathetic behavior
  • affected fish usually stay on the bottom


  • If possible, isolate sick animals immediately
  • Treatment with broad spectrum antibiotic
  • UV lighting to kill any remaining bacteria in the pond / aquarium
  • Filter the water well

More bacterial infectious diseases

There are far more bacterial diseases that can kill goldfish's life quickly. As a rule, they have almost similar typical characteristics to those of Columnaris. The measures required and treatment with a broad spectrum antibiotic are also identical. Two bacterial infections are most common:

  • Chlamydia epitheliocystis - additional identifying features: possible breathing problems and protruding gill covers
  • Tuberculosis - additional distinguishing feature: possible breathing problems
Note: Bacterial infections are very common from new pond / aquarium inhabitants. To avoid this, new fish should ideally be housed in isolation for two weeks. During this quarantine period, it usually shows whether they have any illnesses.

frequently asked Questions

If antibiotics are given to diseased goldfish, isn't it dangerous for the healthy fish in the same water?

No. Antibiotic active ingredients also break down fish bodies almost completely. But as with humans, drug resistance can be the result if they are given antibiotics too often. Then another treatment / another active ingredient must be selected. For this reason, it is important to ensure that bacterial infections cannot spread as much as possible and that new fish do not immediately get into the water with the others, but that it is first observed whether they are healthy or sick.

How do I know if my goldfish are sick when I see them almost only lingering on the pond floor?

This can be a sign of illness, but it doesn't have to be. For example, try to animate the fish to move / swim with a net. This usually shows further signs if there are illnesses. When they are apathetic, they don't move far away, often even poking them without a response. Or do they swim uncoordinated “wobbly”? Can you catch them with the net and examine them for visual signs as described in the article. In any case, the water quality should be tested.

Can goldfish suddenly die of frostbite in the garden pond during the winter?

That depends on the prevailing conditions. When keeping goldfish, a pond must have a minimum depth of 80 centimeters, better one or 1.5 meters. So they can withdraw into the deeper realms, while only the water surface freezes over in the cold and it does not reach the goldfish. It is also important that there is an air hole in the ice layer so that oxygen can get into the pond, otherwise it would suffocate.