Goldfish Tank Size Guide (Minimum Size + Tips)

-- By Carol

Anyone who has ever thought about keeping a goldfish must have heard that it needs a big tank.

How big should the tank be, though? There is always a lot of confusion surrounding this question.

Today we will answer all your queries regarding the size of a goldfish tank in detail. Keep reading to learn more.

Table of Contents

What Should be the Size of Your Goldfish Tank?

There is no one fixed size perfect to meet all your goldfish tank requirements. However, an estimate can be made to stay in the safe zone.

The ideal tank size for a single fancy goldfish is a 3-feet long tank that can hold up to 20 gallons of water.

On the other hand, a single common goldfish requires a tank size of 4 feet in length and a capacity of at least 30 gallons of water.

It is important to note that the tank measurements are only suitable for one goldfish. People usually keep a pair of goldfish, and you will need a much larger tank to accommodate them.

There is a rule that you can follow to ensure that all your goldfish get enough space in the tank. You can use the measurements mentioned above as the starting point.

For example, a single fancy goldfish requires 20 gallons of water. If you add another fancy goldfish, add another 10 gallons of water to the tank.

Similarly, a single common goldfish requires 30 gallons of water, but if you add another common goldfish to the tank, you will have to add another 12 gallons of water.

You can also keep different species in the same tank. In such a case, start by adding 30 gallons for a single common goldfish and then add 10 or 12 gallons of water for each goldfish in the tank.

This is a handy trick to ensure that your tank size is adequate to keep all the goldfish healthy. However, this is not the only method.

Another method can also be used to get an estimate for the goldfish tank. You will have to multiply your goldfish’s potential size by six, which will give you the number for how considerable your tank’s length should be.

One advantage of this method is that you can keep the size of your goldfish tank constant from the beginning.

You will not have to keep upgrading the size of your tank as your goldfish grows.

However, people often mistake multiplying their goldfish’s current size with six rather than their potential size. The potential size is the maximum size your fish can grow into depending on its specie.

The potential size of a fancy goldfish is 6-8 inches, while a common goldfish can grow up to 12 inches. These are the numbers you must keep in mind.

These are two beneficial methods to help you get a fair idea of how big your goldfish tank must be.

Why Does Tank Size Matter for Goldfish?

It is not always necessary to arrange for a huge tank to keep a single goldfish. There are ways to compensate for the size of the tank.

However, keeping them in bowls like new aquarium owners is not advisable.

Sometimes a nano tank is also used to keep a goldfish, but it may not be sufficient to meet the actual tank requirements of a goldfish.

The size of the tank greatly varies depending on your goldfish species too. There are other factors to consider as well before we conclude on the ideal tank size for a goldfish.

So, let’s start by listing these factors that impact the tank size requirements for a goldfish.

What Factors Should Be Considered Before Getting A Tank For Your Goldfish?

The factors to be considered before getting a tank for a goldfish are as follows:

The Species of Goldfish

As already mentioned earlier, the size your goldfish will reach as it grows depends on the species you have.

Certain fancy species grow up to a couple of feet, while a common goldfish can grow twice as big as the fancy species.

You must ensure the tank size matches the species of goldfish you’re getting. You cannot keep a common goldfish in a tank suitable for a fancy species of goldfish.

A small tank will also stunt the growth of your goldfish and will significantly affect the other tank mates.

The Potential Size of a Goldfish

People usually buy small goldfish and keep them in bowls. It grows up to a specific size and then stops. This is usually misunderstood for its potential size.

What most people fail to understand is that a goldfish often grows as big as its tank size. They usually have the potential to grow up to a foot long.

If a goldfish is not given a big enough tank to grow to its full potential, it will stop growing after a specific size and leave some space for it to swim.

Hence, it is crucial to know how big an average goldfish can grow and keep a suitable tank based on it.

The Quantity of Goldfish in a Tank

You may have gotten a big enough tank for your goldfish to swim happily and grow to its full potential.

However, new aquarium owners often make the mistake of keeping two fish in a tank that is only adequate for one goldfish to grow.

You need to adjust the tank size based on the fish population in the tank.

There must be enough space for all the fish to grow to their maximum size and still have enough space to swim around.

The Size of the Initial Goldfish Tank

Another common mistake made by my new aquarium owners is that they keep their small goldfish in a bowl and plan to move them to a bigger tank as it grows.

A goldfish adapts to its environment. If the initial environment is not big enough, they will only grow as much as the tank allows them, and they will stop growing afterward.

Shifting a goldfish to a bigger tank, later on, will not always restart the growth process, and your fish may never reach its full potential size.

Hence, keeping a goldfish in a big tank from the beginning is essential.

Now let’s see how big the goldfish tank should be and what measurements must be kept in mind.

How To Tell If Your Goldfish Needs a Larger Tank?

Even if you regularly feed your goldfish with a healthy diet and maintain clean water conditions, your goldfish will still require a couple of years to reach its full size.

Contrary to popular belief, size is also not the only factor that helps determine if your goldfish needs a bigger tank or not.

If you notice poor water conditions inside the tank, it is an indication that your goldfish needs to be moved to a large tank.

To identify that, check the nitrate and ammonia level of your fish tank’s water.

If there is excessive waste in the tank at one point, even the filter will fail to clean up the water. The only resort at this point is to shift your goldfish to a larger tank with cleaner and healthier water conditions.

Besides this, there is another physical indicator that your goldfish needs a larger tank.

If you notice your little friend having trouble turning around or swimming only in a straight direction, it means that they are suffering from spinal curvature.

Spinal curvature is a common medical condition amongst goldfish, caused by shallow or smaller-sized tanks.

In addition, if you notice your fish’s tail hitting the bottom or wall of the fish tank, it is a clear-cut indication that the tank size is too small for the goldfish, and they need more room to swim freely.

At last, if you notice any scars, scratches, or missing scales on your goldfish, this also signifies that the tank space is too small for the fish. So much so that it starts affecting their physical appearance.

Watch out for the signs above and immediately shift your goldfish to a larger tank, based on the calculation method shared above.

Keeping Goldfish in Small Tanks

Keeping goldfish in small tanks is not advisable as the fish will eventually grow out of the tank and feel uncomfortable in a small bowl or tank.

Moreover, goldfish waste will accumulate inside the tank populating the water and creating unfavorable living conditions for the goldfish.

If you have a small fish tank of around 10-gallon, it is recommended that you keep not more than one fancy goldfish in that tank.

Similarly, for a 20-gallon fish tank, two fancy and one juvenile goldfish would suffice.

In addition, you will also have to ensure that your fish tank is adequately filtered and cleaned regularly, up to 4 to 6 times a month.

If you have a larger fish tank and want to add another goldfish to it, ensure that you add approximately eight to ten gallons of water for each new fancy goldfish.

Similarly, if you want to add a common juvenile goldfish to a tank, ensure you add approximately 18 to 20 gallons of water for each fish.

Don’t forget that you also have to leave room for placing pebbles, plants, and other decoration items in the tank to make your goldfish feel at home and be part of a community.

If keeping a small goldfish tank is your only option, ensure you get a young goldfish that can easily adjust in the tank for a few months.

Once the goldfish starts aging within a couple of months, you must move it to a large tank to ensure that your fish stays healthy and nourished.

Also read: What Fish Can Live in a Bowl?

Tips for Determining Goldfish Tank Size

Let’s look at some practical stocking hacks that can help you get the right tank size.

For an initial goldfish tank size, 10 gallons of capacity is good enough for a couple of goldfish. You may need to shift them to a bigger tank soon so they can reach their adult size. However, for starters, this is a decent size tank.
Follow the rule of 1 gallon of water for each inch of a newly added goldfish in the tank. But you must ensure that there are at least 20 to 30 gallons of water in the tank for the first goldfish.
A slight tweak may be needed in the prior rule for a messy fish or in the case of aggressive tank mates. You will need to add 2 gallons of water per inch of a goldfish rather than 1 gallon for an inch.
Roughly doubling the tank water capacity when more than one goldfish is added can also help in some instances.
A common goldfish will always require twice the tank water compared to a fancy goldfish.

What Should You Add To Your Goldfish Tank?

Once you have determined the ideal tank size for your goldfish, you will need to pay attention to other things in the tank-like decorations.

Decorations and plants in the tank can make the tank look closer to the natural habitat of the goldfish.

Decorations and plants also take up a decent volume in the tank; hence the initial measurements must be made keeping these things in mind.

Goldfish love to swim at the mid-level of the tank. Hence, the plants must be low-lying and should not take up goldfish swimming space.

Goldfish are also known to nibble on live plants. Low-lying grass-like plants are ideal for keeping in a tank with goldfish.

You can also keep fake plants in the tank. But you must ensure that the fake plants are soft and not made of hard plastics.

Plants made of rigid plastics can damage the delicate fins of goldfish.

Hence, it is not just the species or quantity of goldfish that contributes to determining the size of the tank but also the plants and decorations that take up some space.

Also read: 20 Best Plants for Goldfish Tank (with Images)

The Bottom Line

Goldfish are amongst the starter packs for new aquarium owners. They are beautiful and comparatively easier to maintain.

All you need to pay attention to is the size of the tank and the amount and quality of water in the tank.

Hopefully, we have resolved all your confusion regarding the size of the goldfish tank.

You can now easily figure out what should be the appropriate size of the tank for your goldfish and ensure that their health is in check.

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