Today I’m going to shock you with a statement you would expect to hear from an uninformed pet store employee:

Goldfish don’t NEED a big tank.


“You’re joking, right?”

No, I really mean it.

After nearly 20 years of goldfish keeping, I’ve come to realize that all the hype about making sure your goldfish has to have an ocean to swim in is just that…


And this is why:

How Many Goldfish Can You Put in Your Tank?

That, my friend, is the $64 million dollar question.

I’ve seen countless unsuspecting fishkeepers – new and experienced – get totally ripped to shreds (verbally) for posting a photo of their goldfish in “too small” of a tank (or even more horrifying, a bowl) online.

It’s like they might as well have posted:

“I’m an animal abuser who loves torturing goldfish.”

Why all the hate?

Because they’ve broken the unstated “RULES.”

The question is… exactly what rules?

You’ve probably heard any of the following stocking ratios for goldfish:

  • 1 inch of fish per gallon

  • 1 inch of fish per square foot of surface area

  • 10 gallons per fancy fish

  • 20 gallons per fancy fish

  • 20 gallons for the first fancy fish plus 10 gallons for each additional fancy fish

  • 30 gallons per fancy fish

  • 30 gallons per slim-bodied fish

  • 40 gallons per slim-bodied fish

  • 50 gallons per slim-bodied fish

  • 55 gallons per slim-bodied fish

  • Slim-bodies should only be kept in a pond

And these aren’t all.

So you can see that there’s all kinds of ideas floating around out there on exactly how many gallons of water a fancy or a slim-bodied fish needs…

… And precious little evidence to show why one is superior to the others.

No wonder people are confused about goldfish tank size!


When it comes down to it… those “rules” (none of which are in agreement) are just different guidelines people have made up over time, usually based around doing a 25% water change once every week or two and having a typical filter.

The problem?

None of them take into account that you might be able to have lots of plants, more water changes, carefully regulated feeding or greater filtration capacities – things which can really offset having a smaller water volume.

Every situation can vary drastically.

So what it all boils down to is there are no set “rules” about tank size – there are too many other factors at play from fishkeeper to fishkeeper.


Listen carefully now:

Because water volume does NOT have a direct influence on the health of your goldfish (provided the fish can swim around enough to prevent muscle atrophy).

Water quality does.

Tank size can only play a direct role in the following:

  1. How frequently you have to go between water changes
  2. How big of a goldfish you can house (i.e. swimming room)
  3. And (potentially) aggression between more concentrated tank mates.

If you’re a beginner wanting a good starting point – a general suggestion – and you have the space and money, feel free to start out stocking your fancy goldfish tank at 10-20 gallons per fish.

Or 20 gallons, or 30, whatever you like.

A bigger tank means less work for you because the greater water volume dilutes toxins between water changes.

It also means your fish can get bigger comfortably.

This is more desirable if you are wanting your fish to get large.

As the hobbyist, you choose your goals.

If you want to keep a chunky 6-8″ fancy goldfish or even a 12″ slim-bodied fish, there’s no question that you’ll need more space for them (yes, many of them can get that big with the right conditions).

Some find their foot-long single-tailed fish appreciate having as much as 55 or 80 gallons to itself, others feel 30 or 40 gallons is enough.

If you’re looking in your tank and really feel like your fish needs more swimming space, by all means go for it – pets are not fun to keep if you feel like yours is not happy.

As the owner, you know your fish best.

So more power to you 🙂


Some fish don’t seem to appreciate lots of space, others do, sometimes it just depends on the fish.

But maybe you’re just starting out with a little 2″ Comet you brought home from Walmart or a funfair.

Maybe you’re on a tight budget.

And maybe you don’t have a lot of room for a big tank.

Some people will go ballistic and tell you, “That fish is gonna get huge! Don’t you know it can’t live in such a small space?! You need to give your fish away, take it back to the store,” etc.

Not me.

And here’s why:

Goldfish CAN Grow to the Size of Their Tank

Yes, you’ve heard it right:

Goldfish produce a growth inhibiting hormone (GIH) that builds up in the water.

When that water is changed all the time, the hormone is removed and the fish continues to grow.

A bigger tank helps to dilute this hormone, which is why goldfish tend to get really big in a big tank.


In a bowl or small tank, that hormone is very concentrated (unless lots of water changes are done all the time).

So it limits the fish’s growth.

And this is not the bad thing a lot of people think it is.

Many of the oldest goldfish in the world – the ones that have made it into their 30’s and 40’s, at the highest end of a goldfish’s lifespan – are what people would call quite undersized.

Really, they’re just environmentally stunted.

But their unusually long lives prove that they are healthy (an unhealthy, weak goldfish can’t live that long).

(Read more about why stunting isn’t a bad thing here).

Obviously, if your goldfish has already grown big, it’s too late for stunting to happen and it will need a bigger tank in order to have sufficient swimming space.

So only young fish that haven’t grown much should be kept in a smaller space to avoid muscle atrophy problems.

That said:

Even some full-grown adult goldfish will never get to be monsters with tons of space, clean water, nutrition and time.

These can be genetically stunted and can also do quite well in a smaller space.

Related Post: How Big Do Goldfish Get?

More Important than Goldfish Tank Size: Water Quality

Instead of getting obsessed about the tank size itself…

It’s far, FAR more important for a goldfish to be provided with clean water (in my opinion).

The way I see it:

A small, healthy fish is just as legitimate as a big healthy one.

As long as your fish is well-cared for and its needs are met, it’s a matter of preference – what works for your lifestyle and your objectives as a hobbyist.

I’m not going to say you’re wrong! 🙂

But Aren’t Small Tanks Too Dirty or Toxic to be Safe Fish Homes?


There’s this idea that smaller tanks = bad water quality.

Obviously if that was the case I wouldn’t advocate them, because bad water quality is not to be tolerated – clean water is a basic need of goldfish.

Well, from what I’ve observed over the years, goldfish tank size is not to blame for that.

I’ve seen countless people who have a massive, lightly stocked tanks and several filters – with SICK FISH because their water quality is totally out of control.


When a fish is sick in a smaller tank, the issue isn’t the size of the container (like so many immediately assume) – it’s very likely the water itself.


It might take more diligence to balance the water chemistry of a smaller tank…

… But it’s not impossible.  Not by any means.

It’s been done many times.

Focus on having a strong colony of good bacteria, feeding lightly, testing the water and performing water changes when needed and you’re on your way to a healthy environment for your fish.

That said:

I still recommend using an ammonia alert card you can check on daily, especially when you are first starting out with a bowl or a small tank – just to be on the safe side.

It will help give you peace of mind. 🙂

Balancing Matters

Now, if you put 8 goldfish in a 10 gallon tank, it’s going to take a lot effort to keep the water quality under control.

You’ll also have less room for error, and there’s a chance they might pick on each other more.

A word on aggression…

Some people find that they have more problems with aggression when there are more goldfish in a smaller space.

Others don’t have a problem with this.

(And then there’s me, who has one fish in a 30 gallon tank all by herself who won’t tolerate anyone else, so go figure. 😛 )

It can depend on the fish’s individual personality.

My theory is there is less chance of trouble if all the fish are young – and introduced to the tank at the same time rather than one by one.

Sometimes aggression settles down once a “pecking order” is established.


If your tank is totally packed with fish, it’s going to require a LOT of work to keep it safe for your fish.

So if you don’t want to spend your life slaving over them, a big tank can help free up your time.

In a more heavily stocked tank, overfeeding one of the biggest mistakes, followed by inadequate filtration and maintenance.


Clean water isn’t all there is to keeping your goldfish healthy.

Other aspects of their care are just as critical, such as proper nutrition and quarantine protocols.

Wrapping it all Up

I’m sure not everyone is going to agree with me on this.

I also find that most people who criticize those who keep their fish in a small tank or bowl have ironically never owned a goldfish that made it past 10 years old, let alone 40.

But if you have any additional science-backed evidence that proves smaller tanks or stunting is harmful, I’d love to hear it in the comments below.

Have you learned something new?

Drop me a line!

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