You’ve probably heard this before:

“Goldfish are cold-water fish. Keeping them in warm water can harm them.” 

But is that really true?

Today I’m going to show you the actual evidence that will show you the ideal goldfish temperature range for your water, depending on the kind of goldfish you keep.

Keep reading to discover the little-known secrets of goldfish temperature!


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What Water Temperature is Best for Goldfish?

Here’s the surprising truth:

All goldfish are NOT strictly cold-water fish.

There. I said it.

Goldfish breeds are classified into two main categories: slim-bodied or fancy.

Each class actually seems to have their own different preferences.

All goldfish can survive at cold temperatures, but not all will thrive.

Who needs what?

Fancy Goldfish Temperature Requirements

Fancy goldfish are delicate.  Far more delicate than slim-bodied goldfish.

Their organs are packed into a much smaller space.

They have exaggerated body features, like headgrowth, huge fins, or protruding eyes.

They don’t live as long due to being so hybridized.

They are prone to health issues.

Because they are so fragile, having the right temperature is EXTREMELY critical for their overall health.

They won’t die from cold water in and of itself, but it does put more stress on their immune system.

(As pet owners, we should always want to aim for more than “not dying…” right? 😉 )

So what range is best?

Studies suggest that 78-82 degrees F (or 25-27 degrees C) keeps the water the clearest of harmful bacteria, while still allowing for sufficient oxygenation.

They also show the most growth at that temperature.

This is where having an aquarium heater can really come in useful.

Heaters prevent day/night temperature fluctuations (common in smaller tanks) and can keep the water warmer than room temperature.

Unless you live somewhere where it’s really hot year-round, I highly recommend getting one.

I also like the shatterproof kind.


Colder temperatures put additional stress on their immune system and increase bad bacteria in the water.

Over time, it will most likely catch up to these delicate fish.

I won’t say you shouldn’t keep fancy goldfish in a pond that’s subjected to cold winters…

Or that they’re guaranteed to die if you do…

But there is mounting evidence that fancy fish that have to deal with winter don’t cope well with the burden of it in the long-term and tend to do worse year after year.

It’s worth noting that a few kinds of fancies (like Fantails) can deal with this better than others.

It’s true:

Uninterrupted times of warmer water increases their metabolism (part of why they grow more in warmer water), which can lead to a shorter overall lifespan.

This is because the fish isn’t going through winter, which hits the pause button on their lifespan.

But personally, I’d rather try to keep my fish as healthy as possible during the life that they live, rather than risking the numerous bacterial problems fancy goldfish often deal with (which can be fatal in and of themselves) in hopes of a longer life in cooler water.

And there’s also the fact that goldfish who don’t spawn can live much longer than those who do (and goldfish don’t spawn in water at the temperature recommended).

Each goldfish owner will need to determine what they feel is best for their pets.

Still, want a fancy goldfish pond?

A healthy balance could be to keep your goldies outside during the warmer months (spring, summer, maybe early fall) and bring them indoors once the temperature starts to drop).

(Read more about wintering goldfish here.)

Slim-bodied Goldfish Requirements for Temperature

Now let’s talk about slim-bodied goldfish.

You know, the long skinny ones – Commons, Comets, Shubunkins, etc.

These guys are much hardier than fancies.

Much hardier.

They are far more genetically equipped for the combats of pond life and actually do very well in temperatures as low as 65-70 degrees F (18-21 degrees C).

They can also cope with winter way better, and it actually seems to do them quite a bit of good to go through winter.

Coming back to the whole lifespan thing… being able to deal with long winters actually helps slim-bodied goldfish live longer than fancies when they go through a period where time just stops for them physically.

Then come spring, they are ready to spawn like crazy!

Temperature Shock

It’s important to note that sudden, drastic changes in water temperature can cause temperature shock in goldfish.

If it’s extreme enough, it may even kill them!

That’s why it’s recommended to make sure the new water is within 2 degrees of the existing water when performing a water change.

More than that can cause stress.

I always like to use a digital thermometer (the waterproof kind) as it is more precise than using your hands.


A sudden drop to cool temperatures is better than a drastic rise.

Symptoms of temperature shock include:
  • Sitting at the bottom
  • Rapid breathing
  • Lethargy
  • Floating aimlessly
  • Buoyancy problems
  • Excess slime production
  • Surface gulping (when the water is warmed too fast, reducing oxygen)


Extreme swings in temperature can also harm the beneficial bacteria in your filter, even to the point of crashing your cycle and causing an ammonia or nitrite surge.

If you suspect temperature shock, don’t try to bring it back to the original temperature all at once by doing a big water change with cold water – or you can really stress your fish.

After an episode of drastic temperature fluctuations, it is a good idea to use a good quality filter bacteria supplement to help reestablish your culture as fast as possible.

If your aquarium overheated, you can do a few things quickly to help your fish:

  • Use a fan positioned above the tank to blow across the water surface (minimal effect)
  • Place frozen plastic bottles of water in the tank
  • Be sure to increase aeration with a bubble stone to prevent your fish from dying from oxygen deprivation

Maybe you struggle with chronic hot temperatures and keeping your water in the recommended range.

If that is the case, an aquarium chiller might be a good investment.


What do You Think?

Did this article give you some new insight into the best goldfish temperature?

Do you use heaters to control the water in your aquarium?

Leave your comment in the section below!