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Is Goldfish Tank Size Important? The Answer May Surprise You!

goldfish in freshwater

Whether you’re new to the goldfish world or have been keeping goldfish for decades, you’ve likely heard some rule of thumb describing the tank size that goldfish require. The two most common seem to be 1 gallon for every 1 inch of fish and 20 gallons for a single fish with 10 gallons added for each additional fish. You may have even encountered people who accused you of abuse or encouraged you to get rid of your goldfish when they found out you’re keeping a goldfish in a 10-gallon tank. The good news for you is that those “rules” are outdated and not based on science, but for some people, that makes it even more confusing to figure out what size tank to get for a goldfish. Here are the things you should know about the importance of tank size for goldfish.divider-fishbowl

How Important is Tank Size for Goldfish?

tosakin goldfish
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The simplest answer to this question is that tank size isn’t as important as other aspects of tank care are. If you just got a feeder goldfish from the fair or pet store, then your fish will be perfectly happy in a tank smaller than 10 gallons. If you just adopted a 10-year-old goldfish from your friend’s pond, then you’re probably dealing with a fish that is much too large for a 10-gallon tank.

You may have heard that goldfish will only grow to the size of their environment. Interestingly enough, science tells us that’s mostly true. Goldfish release some types of growth-inhibiting hormones, which build up in the water and, essentially, tell your goldfish’s body to stop growing. The more goldfish you have in a given space, the higher these hormone levels will be.

What this doesn’t mean is that you should keep your goldfish in a 1-gallon bowl its entire life, but it does mean that your small goldfish is extremely unlikely to reach 12 inches in length in a 5-gallon tank.

What Does My Goldfish’s Tank Need?


aquarium filter
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Goldfish produce a high bioload, which means their waste products build up rapidly, even in large tanks. A filter that is rated for tanks larger than the tank your goldfish lives in is going to be your best bet for proper filtration. You aren’t going to over-filtrate the water, but you absolutely can under-filtrate the water.

Swimming Space

Aquarium light
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Goldfish enjoy swimming long lengths, which means they do best in long tanks versus tall tanks. Rectangular tanks usually make the best tanks for goldfish, although some cube-shaped tanks can work well. Round bowls and tanks usually do not provide much long swimming space. You should also consider the other things you are adding to the tank. If your goldfish is in a small bowl and you add in a filter, plants, and décor, then you’ve eliminated essentially all of the swimming space in your fish’s environment.


aquarium set up
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You wouldn’t want to live in a room with four blank walls and nothing to do, and neither does your goldfish! These social fish need entertainment and enrichment, which can be achieved with air stones, plants, and various types of décor. Introducing novel items from time to time will keep things interesting, and goldfish will never turn down an interesting snack.

What’s the Most Important Aspect of My Goldfish’s Tank?

It cannot be stressed enough that maintaining water quality is the top priority for goldfish keeping. Your filter can only do so much of the work for you! Invest in an accurate water testing kit that allows you to monitor your tank’s parameters, like ammonia and nitrates, to ensure the water quality is staying in tip-top shape. The smaller the tank or the more goldfish in the tank, the more frequently you’ll need to perform water changes to keep parameters in check. If your goldfish is in a small bowl or tank, you’ll need to perform very frequent water changes, sometimes even daily, to maintain the water quality. Not everyone has the time to dedicate to daily or weekly water changes. It’s up to you to take on what you can handle so you can provide your goldfish the healthy environment it deserves.

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How Many Goldfish Can I Keep in a Tank?

goldfish plant
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There’s no easy answer to this question, and the best answer is for you to use your best judgement. If the environment meets all necessary aspects of a healthy goldfish tank, then you’ve accomplished your goal. If your goldfish have plenty of swimming space, proper filtration, and an enriching environment, then they’re in an appropriately sized tank. Just remember that the more goldfish in a small area, the harder you’ll have to work to maintain the water quality.

What Issues are Associated with a Too-Small Tank?

eggfish goldfish
Image Credit: Csaba Nagy, Pixabay

Goldfish that are kept in small tanks with poor water conditions are prone to ammonia poisoning and nitrate poisoning, not to mention decreased immunity from the stress of a poor environment. Some people report an increase in fin nipping and bullying among their goldfish that are kept in crowded tanks. Not having enough space can also lead to some fish missing out on food if faster or larger tank mates are snatching all the food first. Illnesses can spread rapidly in overcrowded environments, especially those with poor water quality or little oversight to monitor for signs and symptoms of disease. A poorly kept, too-small tank will shorten the lifespan of your goldfish.

divider-fishbowlIn Conclusion

There is no “one and done” rule for the size of tank you should be keeping your goldfish in, but there are special considerations you should take if you choose to keep your fish in a small or overcrowded tank. Goldfish are hardy fish that can live for decades with proper care. Keeping goldfish in nano tanks is growing in popularity, and there’s nothing wrong with that as long as you are maintaining your fish’s environment. Giving your goldfish a healthy home will give them the best shot at a long, happy life!

Featured Image Credit: luckypic, Shutterstock

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