20 Gallon Fish Tank Goldfish: How Many Goldfish In A 20 Gallon Tank?

You intend to set up a 20 gallon fish tank goldfish and don’t know how many goldfish should be kept? This article is for you.

There is nothing more fascinating than having a tank full of goldfish as a pet, and anyone who has ever had the pleasure of having them knows what a tremendously therapeutic experience this can be. If you are brand new to fish ownership, chances are that you will have a multitude of questions related to housing and care, which is perfectly normal. One of the questions we most commonly hear is can they keep goldfish in a 20-gallon fish tank. In this article, we will answer all your questions about the 20 gallon fish tank goldfish.

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Goldfish Need a 20-Gallon Tank!

Before reading the next part, the very first thing we must keep in mind is that the traditional goldfish bowl is not suitable for keeping any types of goldfish for a long run! To grow comfortably and happily, goldfish require at least a 20-gallon tank.

But what are the reasons?

  • Goldfish quickly grow larger in the bowl and need more dissolved oxygen in the water. The small surface area provided by a bowl simply doesn’t meet that requirement.
  • Depending on the variety you choose, goldfish can grow quite large. A fantail goldfish can grow up to 8 inches long and a slim Comet or Shubunkin goldfish can grow up to 2 feet long!
  • Slim-bodied fish go best in a big garden pond, and fancy goldfish prefer a fish tank of at least 20 gallons.
  • Goldfish are not tidy fish, so a small tank will take you more effort to maintain and provide inferior water quality for the fish. These fish also produce a large amount of waste.
  • As a result, regular water changes are required to maintain a safe atmosphere for them. Their life expectancy increases when they are surrounded by fresh water.
goldfish need a 20-gallon tank

How Many Goldfish In A 20-Gallon Tank?

Keeping fish in the tank can be made simple if you follow a simple rule. One-inch fish per one-gallon tank. According to this rule, a 20-gallon tank is large enough to house twenty small goldfish. 

In any case, you must keep in mind that it is not advisable to keep that many goldfish in such a small space. There is a high probability that you will face issues with ammonia and nitrite build-up because the bio-load will be so great that the filter won’t be able to handle it.

When determining how many goldfish you can keep in a tank, there are many factors to consider. To determine the correct number of goldfish for the tank size of 20 gallons, you must also take into account the fish size and the type of fish. 

To ensure your goldfish’s health and well-being, you need to ensure that you provide them with sufficient space so that they can swim freely.

Read also: Two Goldfish In A Tank

Based On Goldfish Types: How Many Goldfish Can You Keep In A 20-gallon Tank? 

Common goldfish

In a 20-gallon tank, you can keep two common goldfish. The common goldfish needs a lot of space. The growth of the goldfish is one of the main reasons for this. The goldfish grows fast, and it can grow up to 2 feet in length. This is the reason why two common goldfish will suffice in a tank of 20 gallons.

Fancy goldfish

You can keep two common goldfish in a 20-gallon tank
You can keep two common goldfish in a 20-gallon tank

If they are one or two inches long, you can keep five to ten fancy goldfish. However, in the case you are planning to grow the fish quickly, you should not keep more than one or two goldfish in a 20-gallon aquarium. 

I have heard the rule of thumb that it takes 20 gallons to keep a fancy goldfish from several people, so it would seem that you could keep one.

Comet goldfish

 You should only keep one comet goldfish in a 20-gallon tank
You should only keep one comet goldfish in a 20-gallon tank

More than five to ten small goldfish can be kept in a 20-gallon tank. However, if you want to keep a comet goldfish in a 20-gallon tank, you should only keep one comet goldfish. Comet goldfish can grow rapidly and reach 12 inches in length when they become adults.

Fantail goldfish

You are only allowed to keep two small fantail goldfish in a 20-gallon tank
You are only allowed to keep two small fantail goldfish in a 20-gallon tank

If you have a 20-gallon tank, you are only allowed to keep two small fantail goldfish in it. That would be a better space for them to swim freely.

If you put too many of them together, your tank will be overcrowded, and they won’t be able to find enough space to live happily.

Can A Goldfish Live In A 20 Gallon Tank?

A goldfish as mentioned above is able to live in a 20-gallon aquarium. It is totally safe for any goldfish to live and swim in the 20-gallon aquarium.

It is sufficient to keep up to 20 little or one-inch goldfish in a single 20-gallon tank. It’s not recommended that you should keep more than two adult goldfish in a single tank if you wish to keep them.

Every adult goldfish, regardless of species, will require a more than 10-gallon tank or space to grow and swim comfortably. The final answer is, of course, yes, a goldfish can survive in a 20-gallon aquarium.

What Goldfish Can Live In A 20 Gallon Tank?

We can say that a 20-gallon aquarium can be the perfect home for almost every type of goldfish. But the size of the goldfish determines how many can be kept in a 20-gallon tank. You may put 15 to 20 goldfish in a 20-gallon tank if they are all one inch in size.

Adult goldfish, on the other hand, cannot be kept in a single 20-gallon tank with more than two goldfish since they may grow to be 2 feet long.

  • Small fantail goldfish: This little goldfish may be kept in a 20-gallon aquarium. If you choose the smallest one-inch goldfish, a 20-gallon tank can contain 20 little goldfish.
  • Adult common goldfish: Adult goldfish may vary in size from 12 to 24 inches. So for a 20-gallon goldfish tank, two adult fish is a perfect number.
  • Adult comet goldfish: This type of goldfish may survive in a 20-gallon tank. However, the 30-gallon tank is preferable for the adult comet.
Factors Affecting The Number Of Goldfish In A 20-Gallon Tank

Factors Affecting The Number Of Goldfish In A 20-Gallon Tank

Now we have known how many goldfish we can put in a 20-gallon tank, let’s move on to the factors that can influence this number.

Goldfish species

The first consideration is the sort of goldfish you have. As previously said, goldfish come in a variety of forms and sizes. As a result, certain goldfish species demand more area than others.

Comet fish, for example, may reach 12 inches in length, but fantail goldfish can reach about 8 inches. This means that you can easily have two fantails in a 20-gallon tank but only one comet goldfish.

In theory, you can raise more than two smaller goldfish in a 20-gallon aquarium. However, keep in mind that goldfish are so active that they require a lot of area to swim. Consequently, we still recommend keeping no more than two fish in a 20-gallon tank.

Tank maintenance

Keeping your fish’s tank clean is important to keeping them healthy. This includes changing the water on a regular basis and sweeping the gravel to eliminate dirt and trash. These actions will contribute to the cleanliness of your fish environment, which leads to the happy of your goldfish’s life.

The number of goldfish you can keep in a 20-gallon tank depends on how often you clean it. Even though goldfish are quite hardy, they are still sensitive to their surrounding environment. A dirty tank can cause a variety of health issues for your fish, including illnesses and infections.

As fish owners, we are responsible for providing a clean and safe habitat for our fish. If you want to keep more fish in your 20-gallon tank, you’ll need to do more frequent water changes and cleanings.

Tank decoration

Regarding fish tank decoration, most hobbyists prefer a vegetated tank with a few stones, driftwood, and the like. That style of tank layout is far more appealing than a basic aquarium devoid of any decoration.

Your fish will enjoy the novelty of new things to investigate and plants to chew on.

However, this requires giving up tank capacity, which may be an issue if you already have many fish in the tank.

A tank with no decorations, on the other hand, may give a greater swimming area and room for your fish.

It will, however, make your fish feel vulnerable and anxious.

So, if you want to keep two goldfish in your 20-gallon tank, restrict your decorations to the perimeter to leave enough space in the centre of the water column for the fish to swim.

You may also utilize a variety of plants as decorations. The level of decoration you may utilize is determined on the size of your tank.

What Fish Can Live Together With Goldfish In A 20 Gallon Tank?

Goldfish are hardy doesn’t mean that it can live with any other species. Keep reading to know what type of fish can co-exist with goldfish in a 20-gallon aquarium.

Hillstream Loach

Hillstream loach

The flat-bodied loach might be the ideal tank partner for your goldfish. They both like living in cool water. But the hillstream loach, which likes to stay close to the aquarium glass. Because of this, the goldfish are unable to remove them. Therefore, a 20-gallon tank may contain both goldfish and the hillstream loach.

Rubber nose Pleco

Rubber nose Pleco

If you want an algae eater, you may choose a rubber nose pleco. It makes an excellent tank mate for goldfish. It can grow to be six inches long and will not be eaten by goldfish. As a result, the rubber nose pleco may share a 20-gallon tank with your goldfish.

Cold Water Minnows

Cold Water Minnows

If you have some fancy goldfish in your 20-gallon tank, you might want to try getting some cold water minnows. Cold water minnows and goldfish may coexist in the same cold water and at the same temperature.

Furthermore, cold water minnows may grow to be 1.5 to 2 inches long. In a 20-gallon tank, they can live with goldfish.

Hog-Nosed Catfish

Hog-Nosed Catfish

Cory catfish cannot be kept alongside goldfish because the goldfish can eat the tiny cory catfish at any time. However, the hog-nosed catfish is a fantastic choice for you.

They are large and appear to be too big for the goldfish to eat. As a result, a 20-gallon aquarium may contain hog-nosed catfish and goldfish.

Special Considerations For Small Tanks

Small tanks, such as 20-gallon tanks, have their own set of challenges. In addition to the tips and rules that apply to bigger tanks, there are a few more issues when stocking a small tank.

Watch out for aggression

Though goldfish are not naturally violent, they can become aggressive if stressed or territorial. This is more likely to occur in a small goldfish tank with little area for your fish to swim and explore. Due to a lackage of space, your fish may grow hostile towards one another, resulting in goldfish fighting and injury.

To avoid hostility, make sure that your fish have a lot of space to swim. We recommend keeping no more than one or two tiny goldfish in a 20-gallon aquarium. If they’re still immature, you might be able to keep 1-4 fancy goldfish together, but it’s best to be safe and keep them apart.

Water parameters should be tested on a regular basis

Another problem when stocking a tiny tank is that water quality can change fast. This is because tiny tanks contain less water, allowing trash and debris to build up more quickly. As a result, it’s critical to evaluate your water parameters on a regular basis and nip potential goldfish concerns in the bud before they become big difficulties.

Special Considerations For Small Tanks

Stick to our 1-2 goldfish per 20 gallons rule to avoid having an overcrowded goldfish tank in the first place. Then you may start using more creative methods to keep your aquarium clear. When choosing protein-based fish food, for example, search for items with fewer fillers and more natural components. These meals are not only healthier, but they can also help decrease waste in your tank.

You should also think about utilizing a gravel vacuum throughout your water changes. Gravel vacuums may assist remove trash and waste from your gravel, which can greatly enhance the quality of your water.

Furthermore, we recommend utilizing a filter built for a tank twice the size of your 20-gallon tank. A larger filter will not only assist keep your water clean, but it will also help minimize stress in your pet fish.

Growth could be slowed

Across all species, the average adult fish body length in the wild is slightly greater than the average home aquarium can accommodate. In reality, most home aquariums are only large enough to house a fish throughout its juvenile or adolescent period of life. As a result, if kept in a tiny tank, your mature goldfish may never achieve their maximum growth potential.

While this does not necessarily imply that your fish will be sick, it is something to consider if you intend to raise goldfish in a 20-gallon tank. Goldfish hobbyists who want to optimize growth frequently choose bigger tanks, such as 30-gallon or 40-gallon tanks.

Video About 20 Gallon Fish Tank Goldfish Setup


How long do goldfish live in a 20-gallon tank?

The life expectancy of goldfish is quite long. They can survive without water for up to three hours. Therefore, with a 20-gallon tank, they will surely survive more than years.
If you want to extend the lifespan of the goldfish, you should keep it in a pond. They can live for 20 years in a large pond.

Is 10 gallons enough for a goldfish?

If you are asking about a 10-gallon tank, I would say that it is only suitable for one or two baby goldfish. Once your fish outgrow the tank, you need to consider at least 20 gallons of space for each additional fish.

Can goldfish live in a bowl?

Goldfish can live a long, happy life in a bowl that holds from three to five gallons. But ideally, an adult goldfish should be kept in a bowl that holds at least ten gallons. This will allow for leeway with water changes when life becomes busy and ensure the quality of the water remains high. 


So, keeping a 20-gallon fish tank goldfish is possible. You have to decide how many goldfish you should keep, ensuring your fish can stay happy and healthy. 

To determine how many goldfish you should keep in a 20-gallon tank, you should consider many factors, such as fish size and fish type. Hopefully, our article has clarified this issue for you. 


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