What is the Optimal Water Temperature for Goldfish?

Some people believe that goldfish are coldwater fish; hence people should avoid keeping them in heated tanks.

If your circle has people who keep goldfish as pets, you may have heard a lot of conflicting information.

We have come up with a guide on what the optimal water temperature for goldfish truly is.

What Is the Optimal Water Temperature for Goldfish?

Goldfish can be kept in a tank or a pond, depending on people’s preferences.

But generally speaking, the optimal temperature is anywhere between 72-75 degrees Fahrenheit or 22-24 degrees Celsius.

For breeding purposes, 26 degrees Celsius is ideal for Goldfish.

When kept in a pond, goldfish are more exposed to outdoor elements like natural temperature changes.

On days when you have cold weather, goldfish will have a significantly reduced activity level, called torpor.

However, a common goldfish is able to withstand temperatures as low as 32-40 degrees Fahrenheit.

What Does Torpor Mean?

Torpor is when the goldfish gets in a state of lethargy, akin to semi-hibernation. While the goldfish are nevertheless awake, they move around quite slowly.

If your goldfish is in this state, there is nothing to be concerned about, as it is part of your goldfish’s natural lifecycle.

When the water temperature rises, the goldfish come out of torpor and start breeding.

People often increase the water temperature when they want their goldfish to start reproducing.

Monitoring the Goldfish Tank Temperature

It is extremely important to keep making sure the temperature of the goldfish tank remains in the optimal range.

One of the instruments used for this purpose is the aquarium thermometer.

There are different types of aquarium thermometers available in the market, each having its own features.

You can easily get a reading of the temperature of the aquarium by using a stick-on aquarium thermometer.

These are best if you want to save money and if you don’t want to adjust the water temperature for mere fractions of a degree.

However, to get the best and most accurate reading, digital thermometers are ideal for it.

Benefits of Warm Water for Goldfish

Goldfish activity levels become noticeably higher in warmer water.

Not only does it allow the goldfish to become a faster swimmer, but it also improves its digestion system.

Warm water can also boost its immunity and help the goldfish fight off certain diseases.

Adjusting the Temperature of Goldfish Water

Now that you know how to read the goldfish water temperature, how do you actually adjust it to make sure the goldfish are comfortable?

There are various methods, but if you want to go for the quickest and easiest one, an aquarium heater is the best option for you.

It is a common perception that a coldwater tank doesn’t require an aquarium heater.

That may be true if the aquarium is placed in a heated indoor area.

Although it won’t cause any fatal problems for the goldfish, temperature fluctuations can still have negative effects on the goldfish’s condition.

If you are planning to buy an aquarium heater, it is best if you buy one where you can manually control the output.

This is because many aquarium heaters have a fixed temperature setting.

These heaters are mostly suited for tropical aquarium tanks; hence there is a high chance of the water becoming too hot for the goldfish to survive.

How Does Water Temperature Affect Reproduction in Goldfish?

The breeding habits of goldfish are much affected by the water temperature and the environment.

The goldfish have evolved to such an extent that in warm water, they are capable of releasing more androgen, which is a reproductive hormone.

However, in cooler temperatures, androgen production is decreased. In this system, the goldfish larvae have a better chance of survival.

If you want your goldfish to start reproducing, the water temperature has to imitate the natural changes and conditions of the environment.

During the spring season, you may increase the water temperature to 25 degrees centigrade.

Conversely, in the winter season, the temperature should be reduced to between 10-12 degrees centigrade.

These water conditions will have a significantly higher chance of having a healthier goldfish larva.

Causes of Fluctuations in Goldfish Water Temperature

There are various factors that can affect your goldfish water temperature, regardless of whether you have an aquarium heater or not.

It is important to ensure your aquarium heater is working properly. Failure to do so will cause it to malfunction.

Therefore, if the water temperature drops, it will cause a lot of problems.

It is much easier to heat the water in case it gets too cool rather than cooling the water when it gets too hot.

Some common factors that affect the water temperature are given below.


If you have placed your goldfish tank near a radiator or a space heater, the water temperature will likely fluctuate and may rise considerably.

Room Temperature

Naturally, the room temperature of where you have placed your goldfish tank will have an effect on the goldfish water temperature.

In winter especially, it is important to make sure the room is slightly heated.

For the summers, you may have to use air-conditioning to regulate the water temperature on a particularly scorching day.

Sunlight and Drafts

Avoid placing the goldfish tank in direct sunlight or near a window.

Sunlight will directly increase the water temperature causing it to easily overheat if you are not careful.

In the winter season, the drafts and sudden gusts of wind will lower the temperature.

Although your aquarium heater should be able to adjust the differences, it is best if you avoid this entirely.

How to Treat Diseases by Adjusting Water Temperature

It is a fact that by adjusting the water temperature, you can treat certain parasitic infections.

However, it is absolutely essential if you get a consultation from a fish vet first.

Once the fish vet has diagnosed the disease, they may recommend changing the water temperature slightly by either increasing or decreasing it, depending on the situation.

Most professionals are of the opinion that if the goldfish is indeed suffering from a parasitic infection, the goldfish water temperature should be increased to 30 degrees Celsius for at least ten days.

However, it should be noted that many of the fish parasites have a high endurance level and can live on to potentially two months, sometimes even more.

The 30 degrees rise in temperature isn’t fatal for the parasites, but it is highly effective in slowing their activity and decreasing life expectancy.

It is also helpful in not only healing the goldfish but also boosting its immunity, making them less prone to diseases in the future.

You can also use Malachite green for a more effective result. This will help lower the stress levels of your goldfish and will make them recover faster.

Some diseases and parasitic infections require reducing the water temperature, like the herpes virus.

A goldfish with herpes virus has a 90% mortality rate if it is living in a water temperature ranging from 20-25 degrees Celsius.

On the other hand, that same goldfish has a 10% mortality rate if the water temperature is around 15 degrees.

Hence the reason why consulting a fish vet is imperative before you start their treatment.

What Else is Important for Goldfish (Apart from Water Temperature)?

While goldfish water temperature is quite important, you should also look out for their acclimation to their environments.

If your goldfish has become used to its surroundings, it can adjust to various temperature changes easily.

When you feel it’s the right time to change the water, you should keep in mind certain factors.

If the aquarium water temperature is around 70 degrees, for example, the refilled water should also have the same temperature.

Any extreme change in water temperature will cause the goldfish to go into shock.

Also, make sure you are changing the water temperature extremely carefully and slowly.

If you want to increase the temperature to a certain degree, do it by 1 or 2 degrees after every 12-24 hours.

Rapid temperature changes will also shock even the toughest of goldfish as they won’t have time to get acclimated to the new settings.

Concluding Remarks

You now know that the optimum water temperature for keeping a goldfish happy and comfortable is between 22-24 degrees Celsius.

You should have no difficulty in taking care of your goldfish.

Should your goldfish start behaving abnormally, consult a vet. Your goldfish may have some other problems which are not immediately visible to you.

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