Goldfish Minimum Tank Size – Choosing the Right Tank

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Tank size is the most important thing to consider when buying or preparing a goldfish aquarium.

If you don’t want to constantly upgrade to a larger aquarium as your goldfish grow, you’ll want to choose the right size for your goldfish from the get-go. There are multiple considerations here.

In this article, I’ll tell you everything you need to know to choose the perfect tank size for your goldfish.

We’ll go over what the ideal tank size is, why it matters, and how to know how many goldfish you can fit in a tank. Keep reading to find out more about this topic!

Ideal Tank Size for Goldfish

There’s a lot of confusion surrounding goldfish and tank dimensions. That’s because there are so many varieties of goldfish to choose from!

Not all grow to the same adult size, so they don’t have the same space needs. But a few things remain true.

Goldfish are active and curious. They need plenty of swimming space to stay entertained. Goldfish are also bottom-dwellers. They need wide floor space and enough room to turn around.

And they might need more space than you assume, but they aren’t territorial. They can get along with tankmates even in more densely populated tanks.

If you’re looking for an exact number, here are some species-specific approximates. Common goldfish need a minimum of 30 gallons. These fish are rapid swimmers and can grow up to 12-18 inches. With regards to floor size, they need a tank that’s at least 4 feet long.

The tank should be wider, rather than taller. For each additional fish, you’ll need 15-20 extra gallons worth of tank space.

Fancy goldfish do fine with at least 20-gallons worth of tank space. Each additional fancy goldfish will require an extra 10 gallons.

Fancy goldfish grow up to 8 inches long at most. They’re also slower, more mellow fish, so they don’t need that much room. A tank with floor space at least 3 feet long should suffice.

Why Is Goldfish Tank Size Important?

Goldfish are peaceful, friendly fish. They’re not territorial and they actually enjoy the company of other fish. Why, then, would you need so much tank space for them? Well, there are three main reasons for this.

First, you’ll have to consider water parameters. Goldfish can get very messy. They’re big eaters and have stocky bodies. They can excrete a lot of waste. Keeping multiple goldfish in a smaller tank can lead to rapid fluctuations in water parameters.

Not something you want for the long-term health of your fish. Excess waste can quickly lead to increases in ammonia, nitrites, and drops in pH, all of which can be stressful and even deadly for fish.

The second reason is competition for food. Keeping multiple goldfish in a crammed aquarium can increase stress levels not only due to water pollution. Feeding time also becomes a source of problems.

Goldfish are very friendly, but they’re not the type to share the goodies. Smaller or slower goldfish get the short end of the stick in this situation. The small fish won’t get enough food to thrive in such conditions.

And finally, cramming too many goldfish in the same space can stunt their growth. If you want your goldfish to grow as large as possible, you’ll want to pay attention to space requirements. There’s also a scientific explanation for why this happens.

Goldfish secrete a special hormone called gamma-aminobutyric acid (GABA). This hormone has a growth-inhibiting action. The more goldfish you keep in your tank, the higher the concentration of this hormone in the water.

And the higher the hormone concentrations, the stronger the growth-inhibiting effect. Constant exposure to high-level concentrations will stop your goldfish from growing and reaching its full-size potential.

How Many Goldfish Can Live in a Tank?

The answer depends on multiple factors. What’s your tank size? What species of goldfish are we talking about? We’ve already covered the minimum tank requirements for Fancy and Common goldfish.

But to make things even clearer, let’s organize the number of goldfish by species and by tank size:

  Tank Size (in gallons)
20 30 40 55 65 75 90 125 150 180
Goldfish Species  
Comet Goldfish 0 0 1 1 1 2 3 5 6 8
Common Goldfish 0 1 1 3 3 4 5 7 9 11
Fancy Goldfish 1 2 3 4 5 6 8 11 14 17
Jikin Goldfish 1 2 3 4 5 6 8 11 14 17
Shubunkin Goldfish 0 0 0 0 1 1 2-3 6 8 11
Wakin Goldfish 0 1 2 3 4 5 7 10 13 16
Watonai Goldfish 0 1 1 2-3 3 4 5 7 9 11
  Number of Goldfish Per Tank

Note that I’ve only included the major goldfish species. There are lots of subspecies, especially when it comes to fancy goldfish. Depending on the strain of goldfish you have, these approximates might vary.

You might also find lower tank volume requirements for some of these species. Goldfish can adapt even to less hospitable conditions, such as smaller aquariums. But I’ve only included the optimal tank sizes in this chart.

Can Goldfish Live in a Glass Bowl?

Absolutely not! This is a common question for newbie aquarists. And there’s no better way to get all the goldfish enthusiasts heated.

You’ll see people with very strong opinions on this topic. Some swear that their goldfish are just fine and happy in a tiny glass bowl. But the overwhelming majority, myself included, strongly advise against this.

There are so many reasons why a glass bowl is a catastrophic idea. Starting with the most obvious issue, they don’t provide anywhere near enough space! Most goldfish need at least 20 gallons worth of tank space to swim freely. Some species need at least 30-75 gallons! Most fishbowls can hold somewhere between 3-5 gallons of water. Quite a long way from the minimum 20-gallons.

The constricted space can lead to developmental issues in fish. It’s true that goldfish won’t grow larger than their aquarium space. But an unnaturally small space like a glass bowl can lead to growth deformities, affecting the fish’s internal organs.

Glass bowls are also a poor choice because they impose needless setup difficulties. The rounded shape and the small space make it very difficult to equip the bowl with a filter.

Let’s not even mention heaters or water pumps. But the issues don’t stop here. There are many other potential problems that apply to both glass bowls, and small fish tanks in general, as we shall see in the next point.

Problems with Small Goldfish Tanks

Fishbowls and nano tanks are all the rage. They come in sizes ranging from 3 to 14 gallons on average.

They’re slick, compact, and they look really cool. Who wouldn’t want a tank that can fit neatly in a bookcase or on a side table?

The impressive aesthetics make these setups very tempting. But you probably know my opinion about this already. Small tanks stink. Quite literally. Small aquariums are unstable and difficult to manage.

Even if you were to keep just one goldfish, the water quality would change rapidly.  Remember, goldfish create a lot of waste.

Due to the smaller water volume, the levels of ammonia and nitrates can increase rapidly. The water will get dirty and smelly very rapidly.

These rapid fluctuations mean more frequent monitoring and maintenance. In the case of aquariums under 10 gallons, you might have to perform daily water changes, on top of running a filter. You’ll also have to siphon the gravel and wipe the aquarium more often.

Small aquariums can experience rapid changes in water parameters. Important values such as temperature and pH can fluctuate in a matter of hours or even minutes.

This is very stressful for your fish, and in some cases, can be fatal. The only way to mitigate these issues is to monitor the water parameters closely.

You’ll have to test the values multiple times a day, to ensure that no wild swings happen. As you can see, small tanks can be more time and energy-consuming. Most importantly, they’re very unhealthy for your fish and come with many potential dangers.


As you can see, the ideal tank size differs slightly depending on the goldfish species. Fancy goldfish are the easiest to keep because they need at least 20 gallons worth of aquarium space.

Exotic species such as Shubunkins do better in 50-75-gallon tanks. There are also some exotic goldfish that do well in smaller aquariums, like the Jikin goldfish.

Whatever species you have or are planning to buy, one rule stands. More room is better than too little!

Goldfish like swimming around and playing. They’re also too messy to keep in small aquariums. Whatever you do, just avoid keeping your goldfish in tanks with a capacity lower than 20 gallons.

Author Image Fabian
I’m Fabian, aquarium fish breeder and founder of this website. I’ve been keeping fish, since I was a kid. On this blog, I share a lot of information about the aquarium hobby and various fish species that I like. Please leave a comment if you have any question.
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