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How Big Of A Tank Does A Goldfish Need 

How Big Of A Tank Does A Goldfish Need 

Goldfish are one of the most common pets – especially for first-time pet owners who want to start keeping animals at home. Unfortunately, due to this reason, they are also the pets that go through a lot of mistreatment, simply due to lack of knowledge of fish keeping. 

Goldfish require at least 10 gallons of a water body to stay in, but are commonly kept singularly in bowls. The size increases per 10 gallons for each goldfish you have.

If you are a beginner fish keeper, this article might come in handy for selecting a perfect tank.

Read on to know more!

Also check: How Many Goldfish Can You Keep in a 10-Gallon Tank?

Goldfish Minimum Tank Size 

The minimum size requirement for a single goldfish is 10 gallons as that is adequate space for growth, exploration, and breathing space.

It is also enough for oxygenation to continue smoothly and is the average tank size, so will be equipped with tank accessories like filters, oxidizers, and lights. 

You will also need a bigger tank if you get more than one goldfish, as the requirements for a goldfish tank are 10 gallons per fish. 


goldfish_typesFancy goldfish, like either oranda, ryukin, or comet, need a bigger tank as these species can grow up to be 12 inches long and will need a 50-gallon space at least. In warmer conditions, even the common goldfish (which can be recognized by a single tail) can grow up to 18 inches in length.

The following is a table that can help you understand what size of tanks a certain species need:

Goldfish Species Average Adult Length Minimum Tank Size 
Common goldfish 9 – 12 inches 4 feet long, at least 40 gallons

Extra 12 gallons per fish

Fancy goldfish 8 – 12 inches 3 feet long, at least 20 gallons

Extra 10 gallons for each fish

Single tail goldfish 12 – 16 inches 15 gallons

Extra 10 gallons per fish

Comet goldfish 10 – 16 inches 75 gallons

Extra 50 gallons per fish

Shubunkin Goldfish 10 – 12 inches 15 – 20 gallons

Extra 30 gallons per fish

Common goldfish 10 – 12 inches 10 gallons

Extra 10 gallons per fish

Fancy goldfish have odd swimming patterns, so they do not need a very deep tank, but a wider one.

Hence, with the following tank size requirements in mind, go for one that fulfills the minimum requirement for your goldfish, as well as space for decorations and equipment. 


Limitations Of A Small Tank For Goldfish

The size of the goldfish bowl does not matter as much as the quality of the water does. A small swimming space does directly add to this problem since it traps food and makes the bowl dirty faster, which is why we recommend you get a bigger tank. 

Growth Of Fish 

When you initially get a goldfish, generally, it is a baby-sized one that does not require a lot of space. Smaller goldfish are only 2-4 inches; you have no idea how big this species can grow, with some reaching even 12 – 16 inches long. Hence, it is better to get a bigger tank from the very beginning. 

Also check: 20 Best Tank Mates for Goldfish

Inadequate Space For Swimming 

Fishes require enough space to swim around and grow – both fancy and common ones have their own reasons. 

Fancy goldfish have longer fins with compact body shapes. Additionally, they also normally have very bad vision and increased head growth, so it is hard to swim in a small bowl.

They do not require very deep tanks, but a wide one will be ideal due to their funny swimming patterns. 

On the other hand, common goldfish are extremely active, swift, and energetic. To keep them mentally happy and give them enough room to swim around, you need a bigger tank. 

Lesser Oxygen 

A major problem with smaller bowls is the water surface area which does not get aerated and as easily oxygenated as a bigger tank does.

You will have to optimize the swimming area by filling the bowl to the brim to make up for the lack of space so that oxygen level requirements are met. 

Loneliness And Limited Entertainment 

This is a lesser-known fact, but goldfish are social creatures who enjoy being around other fish.

They are also compatible with most aquariums, and if you decide to keep two together, you will often see them swimming around, sleeping, or hanging together.

So if you consider getting two of them, one bowl will not be enough. 

When it comes to swimming space, there is no upper level, as fish are creatures of larger water bodies and would always appreciate more room to swim. In a small tank, they can end up getting stressed, which will lead to further problems. 

Frequent Water Changes 

Goldfish let out a lot of toxins as they produce a lot of bioload due to their big appetites. They eat a lot, so the ammonia and nitrate levels of the bowl will also get dirty quicker, and you will have to clean the bowl every day so as to not raise toxicity. 

At least 50% of the water should be changed every day to maintain a clean living environment for your goldfish in a bowl. 

Lifespan Of Goldfish

Goldfish live for a long time – the longest one having survived up to 43 years. Even the general lifespan of the fish is 20 years, which is a long time to live in a small bowl with no fancy decorations or swimming space.

It is cruel to keep a living creature in these conditions, so a larger tank will easily resolve one problem. 


How Do I Keep My Goldfish Alive In A Small Tank? 

A small tank has many limitations that make the life of a goldfish much shorter since there is a lack of space, oxidation, and a proper pH level.

A proper tank also ensures that installation of extra machinery like filters, LED, and oxidizers is easy since most of them are up to date with modern facilities. 

Getting a bigger tank is highly recommended for the longer lifespan of your fish as they can grow in size when temperatures get warmer.

However, even if you have a small tank, for the time being, there are things you can do to better the living conditions of your goldfish.  

More: How Big Do Goldfish Get?

Improve Oxygenation

Oxygen levels can be improved by maximizing the surface area of the fish bowl and filling your bowl to the brim.

Keep it in a spot that receives a lot of air, but never directly under the sunlight. It makes the goldfish grow in size and you will have to get a bigger tank so that your fish do not die. 

You can keep your bowl somewhere under the fan as it helps with oxygenation in the water. Otherwise, you should consider adding a small pump that can help clean up the bowl frequently. 

Avoid Overfeeding Fish

Overfeeding is bad for your fish as leftover food will result in an increase of nitrates and ammonia in the bowl.

It will get dirtier quicker and unhygienic water conditions to result in conditions like swim bladder disease which can be fatal. It can also harm the liver and result in difficult digestion. 

A lot of times, fish are unable to eat up all of the pellets as they are too dry and difficult to break down.

You can always soak your pellets in lukewarm water to soften them up and also cleanse unnecessary toxins from food. It will also prevent the formation of gas which happens from extremely dry food. 

Apart from fish pellets, other clean food items they can eat are frozen greens, spirulina flakes, egg yolk (hard-boiled), brine shrimp, and live plants. 

Add Aquarium Plants

Adding miniature aquarium plants will help with the oxygenation in the tank and also give your fish an interesting environment to live in.

They are a natural filter for your aquarium and can also absorb the CO2 produced by the fish. It will increase oxygen levels and also produce a beautiful look for your bowl.

The following are some bowl-friendly options that also require minimum care for growth and maintenance.

  • Java Moss: Java moss can even grow in the dark and contributes towards keeping the bowl clean by trapping toxic matter. 
  • Brazilian Elodea: Brazilian elodea is a hardy plant that grows super fast in certain climate conditions. Make sure that its growth is allowed by local regulations. 
  • Hornwort: Hornwort is a hardy plant that requires minimum care as it can survive in most water conditions and like Brazilian Elodea, grows even in the dark.
  • Anubias Barteri: Anubias Barteri is a plant that can grow even without being planted into aquarium gravel. They can grow by being half-submersed and need low levels of sunlight to grow. 

Getting plants that require dim light is ideal for fish bowls as aquarium plants grow even in artificial light, which can take up swimming space and raise the temperature.

They can also trap harmful bacteria if water is not changed frequently and grow invasive if not cleared on time. 

goldfish and angelfish

Choose Proper Gravel

Choose the correct kind of gravel for bowls, as you also do not want the substrate to eat up your goldfish’s swimming area. Look out for the following things when buying goldfish bowl gravel: 

  • The pellets should be big enough for your goldfish to not swallow them and cause indigestion. 
  • Even if it’s meant for goldfish only, get the gravel used in aquariums as they are usually of higher quality. If getting gravel from a bigger aquarium, try and score one from minimum fishes or none at all to lessen the risk of disease in your fish bowl.
  • All the ingredients of the gravel should be natural so that the water is not infested with chemicals. In smaller water bodies like bowls, this tends to happen faster. 
  • Get gravel that is also plant-friendly for the survival and growth of your aquarium plants. 

Before adding the gravel to the bowl, give the pellets a good wash with water for hygienic and safety purposes.

Whenever you make a water change, remember to clean your gravel properly as well since it tends to be loaded with waste particles and old food that can increase the nitrate levels. 

You can also clean the gravel from bacteria and fungus by soaking it for 10 minutes in potassium permanganate or in alum water (two teaspoons per gallon) for two days. 

Maintain Quality Of Water

Problems with keeping fish in a tiny bowl are many – quicker algae formation, less space for your pet to move around, and difficulty balancing water parameters.

You need to maintain a healthy pH level (6.5 – 7.5) for the survival of your fish. Make frequent water changes (at least 50% every day) as bowls tend to get dirty faster. 

If you are going to use tap water, then you would have to treat it and rest it for a day to balance chlorine levels. Keep the following conditions in mind when cleaning your fish habitat: 

  • Before you add your fish to the aquarium water, make sure that it is at the correct pH level and temperature.
  • Try not to come in contact with your goldfish when you change half of the water every day and keep it in a separate plastic bag or tank instead.
  • To avoid touching the water as well, you can remove the trapped waste in the gravel by simply moving them a bit.
  • Make sure to clean all aquarium plants and decorations properly without any chemical soap or detergent. 

How Big Can A Goldfish Get In a Small Tank? 

There is a common belief that goldfish grow according to the size of the tank they are put in. While there is no written fact to confirm the belief, certain observations have shown that fish in a tank do stay small (around 2 – 6 inches).

However, a lot of factors except tank size affect the growth of the fish. 

In a small bowl or tank, there is not adequate room for your fish to swim around, limiting exercise. Nitrates and ammonia are also formed more quickly and can lead to unhealthy living conditions. Fish also tend to be bored more often, which may lead to stress or depression. 

All of these factors that are caused by a small tank can be possible for stunted growth, which is why a larger tank is automatically required for the full growth of your fish. 

Related Questions

Can A Goldfish Live In A 1 Gallon Tank? 

Though goldfish can survive in a 1-gallon tank, they will not be living long. A 1-gallon tank is not an appropriate size for any kind of fish. 

Can A Goldfish Live In A 5 Gallon Tank? 

Goldfish can live in a 5-gallon tank, but the lifespan will not be as long as it would if kept in an appropriate-sized 10-gallon tank. 

Can You Keep A Single Goldfish?

It is possible to keep a single goldfish, but like all creatures, they are not solitary by nature, and getting a companion for them is a better way to ensure their content and happy life. 

Final Thoughts

Goldfish are almost always seen in an appropriate water body size – in plastic bags, common bowls, or old glass jars – all of which contribute towards their short lifespan.

Hence, if you are planning to get these little pets for your home, do it the right way by responsibly getting them at least 10 gallons of water to swim around.