Goldfish Tank Size: Why It Could Be Harming Your Fish

If you’re thinking about getting a goldfish, you might be wondering what size tank is suitable for these little swimmers. Well, you’ve come to the right place! In this article, we’re going to dive into the world of goldfish tank sizes and give you the lowdown on how much space your fishy friend needs to be happy and healthy. So, let’s get started!

How Many Gallons Does a Goldfish Need?

When it comes to goldfish tanks, bigger is always better.

A single goldfish needs at least 20 gallons of water in order for them to remain healthy with each new goldfish you add after needing an additional 10 gallons.

Secondly, it’s important to understand that goldfish can grow quite large, depending on the breed. Some can reach up to 10 inches in length, so a tiny bowl or small tank is simply not sufficient. In fact, it’s a common misconception that goldfish can thrive in small spaces when in reality, they require a lot of room to swim and explore.

the filtration system should also be considered when choosing a tank size. Goldfish produce a lot of waste, so you’ll need a filter that can handle the bioload. As a general rule, your filter should be able to process the entire volume of your tank at least once per hour.

What’s the Minimum Tank Size for Goldfish?

Contrary to popular belief, goldfish require much more space than a small bowl or tank can provide.

The minimum tank size for a single goldfish is 20 gallons, and 10 gallons for any additional fish. For example, two goldfish would require a minimum tank size of 30 gallons. Keeping goldfish in a small space can lead to stunted growth, weakened immune system, and a shorter lifespan.

The reason for this minimum tank size is not just a matter of space for the fish to swim. Goldfish are messy and produce a lot of waste, which can quickly accumulate and create toxic conditions in a small tank.

A larger tank will provide more water volume, which dilutes the waste and makes it easier for a filter to keep the water clean and healthy.

It’s also important to note that the shape of the tank matters, not just the size. Goldfish are active swimmers and require a lot of horizontal swimming space. A tall, narrow tank may provide the necessary volume of water but won’t offer enough swimming space for your goldfish. A long, rectangular tank is the ideal shape for goldfish.

In addition to the tank size and shape, other factors play a role in goldfish health and well-being. For example, goldfish prefer cool water temperatures, so their tank should be kept between 65 and 72 degrees Fahrenheit. They also need plenty of hiding places and decor to reduce stress and mimic their natural environment.

Goldfish Tank Size By Breed

If you’re curious about the tank size for your fancy or common goldfish, here is a handy table to help you remember!

BreedMinimum Tank Size
Comet Goldfish20-30 Gallons
Oranda Godfish30 Gallons
Black Moor Goldfish20 Gallons
Ranchu Goldfish20-30 Gallons
Shubunkin Goldfish75 Gallons
Ryukin Goldfish20-30 Gallons
Fantail Goldfish20-30 Gallons
Bubble Eye Goldfish20 Gallons
Veiltail Goldfish20-30 Gallons
Pearlscale Goldfish20-30 Gallons
Telescope Goldfish30 Gallons
Butterfly Goldfish20 Gallons
Lionhead Goldfish20 Gallons

What Happens When A Tank Is Too Small for Goldfish?

While they can often be seen swimming in small tanks, it’s important to understand that these tanks will affect a goldfish’s health and well-being. So, here’s what happens when goldfish are kept in tanks that are too small.

1. Stunted Growth

Goldfish can grow quite large, depending on the breed. But when kept in a small tank their growth can become stunted. This means they won’t reach their full size and will even have a shortened lifespan. In addition, stunted growth can lead to deformities and health problems, such as weakened immune systems and digestive issues.

2. Overcrowding

Goldfish produce a lot of waste, and when kept in a small tank, this waste will accumulate quickly. This can create toxic conditions in the water, leading to health problems for the fish. When there are too many goldfish in a small tank, then it will obviously become overcrowded. When this happens it can cause stress, aggression, and a higher risk of disease.

3. Poor Water Quality

When goldfish produce waste, it creates ammonia and nitrite in the water and the less harmful nitrate. In a properly sized tank with a good filtration system, these substances are converted into less harmful nitrate. However, in a small tank, the waste builds up quickly and can cause dangerous spikes in ammonia and nitrite levels. This can lead to burns on the fish’s skin and fins, difficulty breathing, and even death.

(Find out more about ammonia poisoning in goldfish.)

Increased Risk of Disease

When goldfish are stressed, their immune systems weaken, leaving them more vulnerable to disease. In a small tank, overcrowding and poor water quality increase the risk of disease. As you can imagine bacterial infections, fungal infections, and parasites are all more likely to occur in a small tank with high levels of waste.

Shortened Lifespan

And lastly, the most obvious problem of keeping your goldfish in a tank that is too small is a shortened lifespan and increase risk of death.

How To Tell if Your Goldfish Needs a Bigger Tank?

While a bigger tank is always better for the health of your fish, here are a few tell-tale signs that will let you know it’s time to upgrade. Here are the warning signs that indicate your goldfish needs more room.

1. Difficulty Breathing and Swimming

One of the most obvious indicators of an overtaxed tank is difficulty breathing or swimming in your goldfish, such as swimming sideways. If your fish is having difficulty moving around, gulping at the surface, or laboring to stay afloat, it’s likely that they need more space in their tank.

Overcrowding can cause stress and oxygen deficiency in fish tanks; this in turn can make it difficult for your goldfish to breathe properly. And a whole range of health issues such as swim bladder disease and dropsy.

Lethargy and Loss of Appetite

Goldfish who are in a tank which is to small will display symptoms such as lethargy, hiding from other fish, and even loss of appetite. These behaviors may indicate that something isn’t quite right with their environment; a cramped or overstocked tank can lead to overcrowding issues which will eventually hurt their health.


Goldfish can become territorial, especially if their tank isn’t big enough. If you notice your goldfish chasing or attacking other fish in the tank, it could be a sign that it needs more space to claim its territory.

The Quality Of The Water Is Getting Worse

The water quality of an aquarium that’s too small will suffer quickly which causes an increase in ammonia levels. Poor water quality leads to increased stress levels and makes it difficult for your fish to thrive; look out for cloudy water or changes in temperature and pH levels as warning signs that you need an upgrade.

What Size Tank Do I Need for 1 Goldfish?

When it comes to tank size for goldfish, the general rule of thumb is to provide at least 20 gallons (75.7 liters) of water per adult fish. This may seem like a lot, but it’s important to keep in mind that goldfish can grow up to 10 inches (25 centimeters) in length, depending on the species.

On top of this, they are active swimmers and need plenty of space to move around, as well as enough water volume to dilute their waste.

In addition to the 20-gallon minimum, it’s worth noting that goldfish do best in larger groups. If possible, it’s recommended to keep at least two or more together in a larger tank. This not only provides more social interaction for the fish but also helps dilute their waste and creates a more stable ecosystem.

How Many Additional Gallons Does Each Goldfish Need?

The minimum recommended tank size for one goldfish is 20 gallons, however, each additional fish will need an additional 10 gallons of water.

Goldfish can grow fairly large depending on their breed and will require more space than a smaller fish. Having enough room for multiple fish means that they won’t feel cramped or overcrowded; having an overstocked aquarium could lead to poor water quality from too much waste and may cause stress or illness in your fish.

It’s important to be mindful of how many goldfish you plan on keeping before purchasing your aquarium; adding too many can quickly become overwhelming and difficult to maintain – not only from a water quality standpoint but also financially speaking (larger tanks mean more costly filtration systems).

Additionally, you’ll want to make sure that everything else within the aquarium (such as substrates, rocks, and decorations) don’t take up too much space which could have been used by your fish instead.

What Will Your Goldfish’s Tank Need?

If you’re considering keeping goldfish as pets, it’s important to provide them with a suitable habitat that meets their needs. Goldfish require specific tank conditions in order to thrive, including proper water quality, temperature, and space. here are some of the key components of a goldfish tank, so you can ensure your fish have a happy and healthy home.

1. Tank Size

One of the most important factors to consider when setting up a goldfish tank is size. Goldfish are active swimmers and require plenty of space to move around, so a larger tank is better. Provide at least 20 gallons of water per adult goldfish. This will not only give your fish plenty of room to swim but also help dilute their waste and maintain good water quality.


Goldfish are notorious for producing a lot of waste, which can quickly build up in the tank and harm the fish if not removed. A strong filtration system is essential for keeping the water clean and healthy. Look for a filter that can handle at least 2-3 times the volume of your tank, and clean it regularly to prevent clogs and maintain optimal function.


Substrate is the material used at the bottom of the tank that helps maintain water chemistry and provides a home for beneficial bacteria to grow. Gravel or aqua sand are good options for goldfish tanks, but make sure you avoid substrate with sharp edges, which could injure them.


Goldfish are coldwater fish and prefer water temperatures between 65-72°F (18-22°C). Avoid drastic temperature fluctuations, as this can stress the fish and compromise their immune system. Use a thermometer to monitor the water temperature and adjust the heater or cooler as needed to maintain a consistent temperature.


Goldfish appreciate plenty of hiding places and things to explore in their tank. Adding plants, rocks, and decorations can provide shelter and stimulate their natural behavior. However, be careful not to overcrowd the tank with too many decorations, as this can make it difficult to clean and compromise water quality.

Appropriate Lighting

Lighting plays an important role in keeping your goldfish healthy and also creating an aesthetically pleasing environment. Choose lighting appropriate for underwater life and make sure it isn’t too intense, as this can cause stress to your goldfish. Additionally, it’s best to limit direct sunlight on the tank as it may cause algae growth.

Did you know if your goldfish doesn’t get enough light they can start to turn white?


Here are some frequently asked questions people have about their goldfish’s tank size

Is 2 Gallons Enough for 1 Goldfish?

No, two gallons is not enough space for a single goldfish. As a general rule, the minimum tank size for a single goldfish is 20 gallons—although this could be higher depending on the variety of your fish. It’s important to remember that additional gallons are also required if you are keeping more than one goldfish in the same tank.

Will a Goldfish Grow to The Size of Their Tank?

A goldfish won’t grow to the size of their tank, however, they can be stunted by the size of their tank. So ensure you’re keeping your goldfish in a tank big enough to keep them healthy.

Can You Keep Goldfish in A Bowl?

You should avoid keeping your goldfish in a bowl since it doesn’t provide them with enough space or proper filtration. Goldfish need plenty of room to swim around freely without getting stuck in tight spaces, so make sure you choose an appropriate tank size based on the variety and size of your fish.

Can Different Species of Goldfish Live in The Same Tank?

Different species of goldfish can cohabitate peacefully in the same tank, provided they have plenty of space and similar water quality needs. However, it is important to research each fish variety carefully before mixing different species together, as some breeds may be more aggressive or require higher water temperatures than others.

Goldfish Tank Size_ Why It Could Be Harming Your Fish


In conclusion, when it comes to goldfish tank size, bigger is definitely better. Goldfish require plenty of swimming space and ample filtration to thrive, so it’s important to choose a tank that’s appropriate for their size and number.

While it may be tempting to opt for a smaller tank, it’s important to remember that overcrowding can lead to health problems and a decreased quality of life for your finned friends. So, if you want your goldfish to be happy and healthy, give them plenty of room to swim, play, and explore!

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