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Home > Goldfish > Nano Goldfish Keeping: Vet-Approved Guide

Nano Goldfish Keeping: Vet-Approved Guide

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Dr. Luqman Javed Photo

Reviewed & Fact-Checked By

Dr. Luqman Javed

Veterinarian, DVM

The information is current and up-to-date in accordance with the latest veterinarian research.

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For years, there was a lingering belief that goldfish were suitable for fish bowls. There are a lot of misconceptions in fish keeping, and one of the most prevalent is the belief that goldfish should only be kept in bowls that are far too small for even a single fish.

Thankfully, people are becoming more aware of the science behind fish keeping. This increased knowledge has led to questions about the viability of nano tanks. It’s important to understand the risks of a nano tank, though, especially when keeping heavy bioload producers like goldfish.


What is a Nano Fish Tank?

A nano tank is typically considered to be any tank that is 5 gallons or smaller. Some people would consider tanks up to 10 gallons to be nano tanks.

Nano tanks can be a great option for people with limited space because the tanks themselves don’t take up much space. This makes them suitable for places like desks and offices, bedrooms, apartments, and dorm rooms. It’s easy to see why there would be appeal to keeping a nano tank. They’re often marketed as beginner tanks because of their small size.

square goldfish tank with overhead light
Image credit: Karl Muscat, Unsplash

Do Nano Tanks Require Less Maintenance?

It’s a misconception that a nano tank would require less maintenance and cleaning than a larger tank. The maintenance may be less in that you are changing less water with water changes, but the overall cleaning and maintenance schedule is not reduced. In fact, with heavy bioload producers, you may have more frequent cleaning and maintenance needs than you would with a larger tank.

The reason that you may have increased maintenance needs with a smaller tank is because the tank will get dirty more quickly. You also are likely to have less filtration in a small tank than you would in a larger tank, which means your tank’s nitrogen cycle may not be able to keep up on clearing waste products, like ammonia and nitrite, from the water like it would be able to with a larger tank.

Can Goldfish Be Happy in a Nano Tank?

At a glance, a nano tank seems counterintuitive to goldfish care. Their high bioload, large adult sizes, and activity levels render most nano tanks impractical for long-term housing. However, nano tanks can be useful for the goldfish keeper in many situations.


This is perhaps the most useful aspect of a nano goldfish tank. They are ideal for housing goldfish babies, otherwise known as fry. Goldfish cannot be housed with their parents as these fish have no parental instincts whatsoever (they will even eat their eggs if given the opportunity).

When goldfish are born, they are exceptionally small. They are 3/16″ (4.5mm) in length. This is less than half a centimeter in size! Even when they are free-swimming, they are relatively small, at 7/32″ (5mm) in body length.

Goldfish tank with gravel substrate
Image Credit: Hineck, Pixabay

This is where nano tanks come in. They are excellent nurseries for goldfish fry, and because of their size they can easily be stacked or placed in close proximity to each other – this helps when it comes to feeding, rehoming, and sorting your goldfish fry as they grow.

In addition, there are other reasons why you shouldn’t house them in a tank that’s too large:

  • It’s more difficult to monitor small groups of goldfish fry in a very large tank.
  • The large open spaces in a large aquarium will likely scare your fry into hiding, as they instinctively fear large open swimming spaces (because a predator might be lurking around).
  • Fry have to swim greater distances in a larger aquarium to acquire food, which means they spend more energy, and therefore their growth is slower in larger aquariums.
  • The built-in filters in large tanks are often too strong for fry to cope with. The wrong filter inlet may even suck away some fry and trap them in the filter itself.
  • Smaller volumes of water changes are generally more convenient and less stressful for newborn fish.


If you’ve ever been admitted to a hospital, you might recall being placed in a room with a comfortable bed for closer monitoring and treatment either before a procedure or for recovery from an ailment or illness. A nano tank can serve a similar purpose for your goldfish by acting as a hospital tank for a sick individual.

Temporarily placing sick goldfish in the nano tank will help you monitor them closely as they recover. Your goldfish may also appreciate the opportunity to rest and recover in peace in a small space rather than finding a hiding spot in a large aquarium, where other fish might disturb them.

Ryukin Goldfish
Image By: Ek Ing, Shutterstock

In addition, because sick goldfish are often weak, they sometimes don’t get their fair share during feeding time when housed with other fish. In a nano tank, they can eat at their pace without the risk of a greedy tank mate stealing their morsel. Since nutrition is a big part of recovery from a disease, this is a great perk of a nano tank.

Finally, many aquarium medicines come in a liquid form that you have to dilute according to the water volume in your tank. In a nano tank, you would use less medicine. This would save you money and product in the long run.


Though plastic bags are the preferred choice when it comes to transporting fish, some goldfish may just grow far too big for a plastic bag. It’s hard to find a bag large enough to hold a 12-inch individual for a trip. In such a circumstance, a nano tank might be a better transport option for your fish. Please be mindful that because 1 gallon (3.8 L) of water weighs 8.3 lb (3.8 kg), even a small aquarium can be extremely heavy relative to its size.

a calico wakin goldfish in an aquarium
Image By: JuanCarlosPalauDiaz, Shutterstock

For especially long trips, a nano tank with a lid might be a better option than a plastic bag, because it could be easier to aerate for such a journey. A small hole can be drilled into the lid to pass an air tube through, which can then be attached to an airstone in the water of the aquarium. Outside the tank, the tube can be attached to an air pump that can be powered by your car or a spare battery. It’s also easier to perform small water changes in a nano tank during your trip because if a plastic bag is sealed with oxygen, it will instantly lose the oxygen once you open the bag for a water change.


Finally, even when not being used to house goldfish, nano tanks can be a great addition to your aquariums as you can use them to grow food for your goldfish. This can be in the form of plants or any live food you prepare for your pets. Propagating live feed at home is often more cost effective in the long run, and has the added benefit of controlling what you feed the food before you provide it to your fish. Store-bought live food might not be as nutritious and might at times carry pathogens you wouldn’t want in your aquarium.

brine shrimps in a tank
Image By: Napat, Shutterstock

Will Goldfish Outgrow a Nano Tank?

There is a little bit of science and a lot of guesswork required to answer this question, but the simple answer is that it depends.

Goldfish can produce growth-inhibitory hormones, such as somatostatin. In nature, these hormones are used to reduce competition by suppressing the growth of other fish. In a tank situation, with the lack of regular water changes and a small aquarium, this hormone can build up and suppress the growth of the goldfish that produces it.

These hormones are generally not ideal for goldfish to live in. They would have anti-nutritional effects and are known to suppress the immune system. With sufficient water changes, a goldfish could theoretically outgrow a nano tank. However, without any means of measuring the hormone levels in the water, it wouldn’t be possible to know how frequently these water changes must be performed.

If you're new to the world of goldfish keeping or are experienced but love to learn more, we highly recommend you check out the best-selling book, The Truth About Goldfish, on Amazon.The Truth About Goldfish New Edition

From diagnosing illnesses and providing correct treatments to proper nutrition, tank maintenance and water quality advice, this book will help you to ensure your goldfish are happy and to be the best goldfish keeper you can be.

Is Growth Stunting Harmful to Goldfish?

It’s unclear if growth stunting is harmful to goldfish. The goldfish that holds the record for the longest lifespan was a carnival prize goldfish named Tish. He lived to be 43 years old and only reached around 4.5 inches in length. Nobody knows if Tish’s growth was stunted due to living in a bowl for some time or if he was simply genetically predisposed to a small size.

There aren’t any studies that show a strong link between just growth stunting and health problems. However, some goldfish experience growth stunting due to living in a high-stress environment, like living in a tank with poor water quality. Therefore, the prevailing consensus is that stunting is harmful for fish. It is also considered harmful because it isn’t something that would happen naturally to a goldfish in nature. Anecdotally, some goldfish have developed unusual problems, like curved spines, after being kept in a too-small tank or bowl for an extended period, but these problems sometimes fix themselves once the goldfish is moved to a larger tank.



In Conclusion

Keeping a goldfish in a nano tank is a time and effort commitment that many people cannot commit to. There is a large amount of care required to maintain high water quality and your fish’s health in the long run. It’s important to understand that goldfish can live for many decades, so they are not a short-term commitment, especially when provided with excellent care.

If you choose to keep goldfish in a nano tank setup, you need to be prepared for an upgrade soon, as it isn’t considered a good long-term option to house them in.

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Featured Image Credit: Skumer, Shutterstock

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