Do Goldfish Need A Heater? (Indoor & Outdoor)

“Do goldfish need a heater?” This is one question a lot of goldfish keepers may ask themselves when starting out. However, it isn’t as simple as a yes or no answer. In this article, you’re not just going to find out whether goldfish need heaters or not. You’ll also learn what temperature goldfish need to survive, what happens when the temperature becomes too low or high, what happens if the temperature changes too, and whether outdoor goldfish need a heater.

So keep reading to find out more!

What Is The Ideal Temperature For Goldfish?

The ideal temperature for goldfish really depends on what type of goldfish you have. Common goldfish are the hardiest and can survive in temperatures between 39-75°F. However, ideally, the temperature should remain between 60-70°F.

If, however, you’re looking after fancy goldfish, the temperature they need will differ depending on what type you have.

What Temperature Do Fancy Goldfish Need?

Different types of goldfish are going to need different temperatures. So before you purchase one, it’s important to make sure you know what temperature they need. (As you’ll find out later if you don’t get the temperature right, a lot of problems can begin to occur.)

Here are the temperatures different fancy goldfish need:

  • Japanese Tamasaba goldfish – 60-70°F
  • Fantail Goldfish – 75-80°F
  • Lionhead goldfish – 60-75°F
  • Bubble Eye goldfish – 70-80°F
  • Phoenix goldfish – 65-72°F
  • Oranda goldfish – 65-72°F

As you can see, the temperature varies depending on the fish. This is partly due to the way they’ve been bred and that some are also more susceptible to disease than others.

So Do Goldfish Need A Heater?

As you can see from the temperatures goldfish need above: Whether or not a goldfish needs a heater depends on the type you have. If you’re keeping common goldfish, you won’t need a heater; however, most fancy goldfish breeds will definitely require a heater to keep them healthy.

Can You Put Goldfish In A Heated Tank?

You may also be wondering whether it’s possible to keep goldfish in a heated tank (i.e., with tropical fish). Well, as long as all the water parameters are met and make sure they can both live happily at the same temperature, it’s entirely possible to add goldfish to a heated tank.

As well as looking at the temperature, you’ll also need to make sure they need similar pH levels and environments too.

Also, goldfish are much more likely to breed when the tank is warmer, so you’ll need to prepare for this when you’re adding your goldfish to a heated tank. And if you’re going to add a goldfish to a heated tank, you should also make sure you’re oxygenating the water more for them, as warmer water can’t hold as much oxygen.

(As well as a filter, you should also consider adding a filter and air pump to the tank.)

Do Goldfish Kept Outside Need A Heater?

Goldfish that are left outside will rarely need a heater. As long as the temperature of the water doesn’t fall below 39°F, then they are able to survive. This is because they go into a dormant, almost hibernation mode, where they stop eating and remain near the bottom of the pond where it’s warmer.

However, that doesn’t mean you should just leave your pond. You should make sure that if the pond freezes over that there’s a hole in the ice where oxygen is able to enter, and carbon dioxide is able to leave.

One of the best ways to do this is to get a deicer. Deicers hear up the water around them, making sure that a hole remains for the gas exchange to occur. While they won’t heat the pond entirely, they’re definitely not going to harm the temperature.

But of course, if you’re willing to shell out for a pond heater, then your goldfish will definitely be grateful. While they can survive in low temperatures, it’s never going to be as pleasant for them as water that’s between 60-70°F.

And, of course, this advice isn’t the same for fancy goldfish. If you’re keeping fancy goldfish in your pond, then you’ll need to make sure the water temperature doesn’t fall below their suggested parameters.

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What Happens If The Temperature Becomes Too Cold?

When the temperature becomes too cold for your goldfish, you’ll notice a few different things happening. And if you spot them (especially in fancy goldfish, you should do anything you can to raise the temperature).

Here are the most common things that are likely to happen when the temperature is too low.


First of all, you’ll notice that your goldfish is acting lethargic and not moving around as much. If they’re common goldfish, you may notice that they stop eating altogether. If you’re keeping them in a pond, you should stop adding food when you notice they stop eating, as it will only pollute the water.

If you’re keeping fancy goldfish, however, the temperature in the tank should never drop to the point where they become lethargic.

More Susceptible To Disease

If your goldfish become lethargic, it’s because their metabolism has slowed down dramatically. This isn’t healthy for them, and it will often result in a weakened immune system which means they’re going to be much more susceptible to disease.

Stunted Growth

You may also notice that if your goldfish haven’t reached their full size yet that their growth will be stunted. When the water is too cold, they’re not going to be eating as much. Therefore they won’t have as much energy or nutrition to grow, and they won’t reach their full size.

While this may seem like a good thing, many harmful effects can be associated with stunted growth.

What If The Water Gets Too Hot?

You may think that if the water gets too hot, it won’t be as harmful. But this simply isn’t true. Water that’s too hot for your goldfish is going to be just as dangerous as water that’s too cold for your goldfish.

Here are some of the problems that can occur when you keep your goldfish in water that’s too hot for them.

It Will Affect The Bacteria Levels

If the water becomes too hot in the tank, one of the first things to be affected is the bacteria levels. The beneficial bacteria that keep the ammonia levels low can die off, which will cause ammonia spikes that can often be fatal.

As well as this, bacteria, as well as fungus and parasites, often thrive better in warmer water. This means that your goldfish are much more susceptible to diseases, especially when combined with the next fact.

They’ll Become Stressed

As well as this, when the waters are hotter, it’s also going to stress your goldfish out. Their metabolism is going to speed up, which wreaks havoc on their body. All of this is going to weaken their immune system. And when their immune system is weakened, they’re much more likely to suffer from a disease of some kind.


When the water gets warmer, it isn’t going to be able to hold as much oxygen in it as cooler water. As you know, fish breathe by drawing out oxygen from the water. This can be worked around by adding an air bubbler to the tank.

What Happens If The Temperature Changes Suddenly?

While the temperature being too high or low is bad, what’s worse is when the temperature changes suddenly. If the temperature changes too quickly, then it could be extremely dangerous for your goldfish.

Temperature Shock

The most likely thing to happen is that your goldfish will suffer from temperature shock. Temperature shock is extremely fatal and will kill your goldfish in a matter of minutes.

This is why it’s so important to make sure that if you’re keeping fancy goldfish, you use a heater to ensure the water remains at the right temperature.

Respiratory Problems

As well as this, if the water temperature rises too quickly, then the oxygen will leave it faster. And, of course, when this happens, your goldfish is going to have a much harder time breathing.

When this happens, you may notice them gasping for breath or that their gills are moving really fast.

Make Sure You’re Using A Thermometer

And lastly, make sure that you’re using a thermometer when you’re using a heater for your goldfish. A thermometer will help you notice if the water is too hot or too cold and allow you to adjust it accordingly.

If you’re not sure where to get thermometers, luckily, you can pick them up extremely cheap off Amazon.


Now you know the perfect temperature for goldfish, as well as how to keep them at the right temperature.

Remember, when the temperature gets too hot, your goldfish is going to suffer. The oxygen levels will drop, they’ll become more stressed out, and the chances of disease and illness are going to rise.

If the water gets too cold, then they’re going to become lethargic and stressed as well.

And most importantly, you also need to make sure that the water temperature doesn’t fluctuate too much either. When that happens, your goldfish can go into temperature shock, which can become fatal in minutes.

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