Is a 30 Litre tank big enough for goldfish?

Goldfish tank size is really important! In fact, the goldfish tank size you choose when you first buy your fish is one of the most important decisions you’ll make while caring for your fish.

The reason that goldfish tank size matters so much is that goldfish need a big tank. Much bigger than most people think!

You see, as well as thinking about the current size of your fish, you need to think about the potential size of your fish too. This is because you don’t just have to give your goldfish enough room for today.

You need to give your fish room to grow.

It’s important to realize that the goldfish you buy from a pet store are very young. They haven’t yet reached anything close to their full adult size. And you might be surprised to learn just how big goldfish get…

Common goldfish can easily reach 10 inches and fancy goldfish regularly reach 8 inches in length.

Imagine trying to fit an 8-10″ fish into a goldfish bowl! It just wouldn’t work. Your fish would suffer and it wouldn’t live very long at all. That’s why you need to give your goldfish a nice big tank or pond.

The goldfish tank size you choose will depend on whether you have a fast-swimming, slim-bodied fish, like a Common, Comet or Shubunkin goldfish, or a slower-swimming fancy goldfish.

Common and Comet goldfish tank size

For Common goldfish, Comets and Shubunkins, we recommend a tank measuring at least 4 feet long with a volume of at least 30 gallons.

Of course, it’s a case of the bigger the better! So any more than this is great too.

If you plan to keep more than one goldfish in your tank then add an extra 12 gallons for each additional fish.

While it is certainly possible to keep Common and Comet goldfish in a tank, they can grow so large – and are so fast swimming – that they are really better suited to living in a pond.

Fancy goldfish tank size

For fancy goldfish, we recommend a tank measuring at least 3 feet long with a volume of at least 20 gallons.

If you plan to keep more than one goldfish in your tank then add an extra 10 gallons for each additional fish.

What if I have two goldfish?

Based on the rules above, the goldfish tank size we recommend for two goldfish is:

• 42 gallons for two Common goldfish. That’s 30 gallons for the first fish and 12 additional gallons for the second fish.
• 30 gallons for two fancy goldfish. That’s 20 gallons for the first fish and 10 additional gallons for the second fish.

You might have noticed that 30 gallons is the recommended figure for a single Common goldfish or for two fancy goldfish.

If you have a 30 gallon tank and are thinking about which goldfish to buy, this might help you make your choice!

What if I have more than two goldfish?

You can, of course, use the rules above to work out the goldfish tank size you will need for any number of goldfish. However, in most cases, you’ll find that keeping more than two goldfish is impractical.

The majority of people simply don’t have enough space for the tank size that would be need for that number of goldfish.

For example, even three common goldfish would need a tank size of 54 gallons (30 gallons + 12 gallons for the second fish + another 12 gallons for the third fish).

Most people won’t have a goldfish tank that size.

If you want to keep lots of fish, we recommend choosing a smaller fish than goldfish!

How to calculate tank size?

If you’re reading the above and wondering what size your goldfish tank is, don’t worry – there’s an easy way to work it out.

To calculate your goldfish tank size, you need to take three measurements.

First, measure how long the tank is, from left to right.

Then, measure how wide the tank is, from front to back.

Finally, measure how deep the tank is, from top to bottom.

Once you have those numbers, put them into this fish tank size calculator.

That will give you the number of gallons for your goldfish tank. You can then use the rules above to work out how many adult goldfish you can safely keep.

Similar Goldfish Tank Posts

I have a 30 litre biorb with two goldfish 1.5" length, estimated 5 years old.

For the last couple of days one fish has laid on its side (still breathing) at the bottom of the tank. It occasionally moves sideways along the bottom of the tank but this is increasingly rare as it weakens.

The other fish is very healthy.

I change 1/3 of the water monthly and add a new service kit, water treatment, bio liquid etc.

Anything I can do for the fish?

#2

6 years ago

Oh my! That is way way too small for one goldfish never mind two. They are poisoning themselves with their own waste. You need to be looking into a plastic storage container temporarily until you can fix the problem. Buy the the biggest you can find and fit a filter in it.

#3

6 years ago

Carley is right...my five year old Goldies are at least 8 inches in length!
Until you can get a proper sized container for them do at least one 50% water change daily to keep them both alive. They are literally being poisoned by their own waste in that tiny container.
All fish tanks, even correctly sized ones, need at least a 30 - 40% water change weekly, not monthly, to keep their water buffered with proper minerals and to dilute the toxins released by their waste and respiration. Goldies are exceptionally dirty fish and require much more frequent water changes of larger amounts.

#4

Tom

6 years ago

Thank you for your comments.

I genuinely don't like to question your judgement or expertise, but biorb does recommend that 2-3 fish of this size are kept in a 30 litre biorb.

The fish have lived in the aquarium for 5 years with no problems. The suddenness of this problem has taken me by surprise. Particularly since the other fish is perfectly healthy.

#5

6 years ago

I posted your stocking in the well respected stocking site, www.aqadvisor.com, using an 8 gallon tank since they did not offer the 30 liter as a choice. Even with the 8 gallon being larger the following results were given:

Warning: Goldfish is not recommended for your tank - it may eventually outgrow your tank space, potentially reaching up to 12 inches.
Recommended temperature range: 19 - 23 C. [Display in Farenheit]
Recommended pH range: 6 - 8.
Recommended hardness range: 5 - 15 dH.
Your tank is too small - it will require massive amount of frequent water changes each week!

Your aquarium stocking level is 400%.
Your tank is seriously overstocked. Unless this setup is temporary, you should consider a larger tank

My five year old goldfish could NOT physically fit into a 30 liter tank, which is an indication of the serious stunting that has occurred with your two fish. Not all fish are affected by the same toxins at the same rate, just like not all humans exposed to a contagious virus will get sick, but your overcrowding in this tank is serious enough to definitely cause serious issues, most likely premature death, with BOTH fish.
Goldfish have an expected life span of 20 years... please upgrade your tank size so your two will have a chance at achieving even half of that.

Those may interest you:

#6

Tom

6 years ago

Thank you for your help. I'm not sure if you are familiar with ReefOne or the BiOrbs, but it seems that they are seriously mismarketing their products.

#7

6 years ago

Sadly, Tom, that is why fish forums like MAC have such mixed reviews. People are told stuff like you were, then something happens like your ill fish and the truth comes out. No one wants to believe their retailer or manufacturer doesn't know what they are selling, right?
Manufacturers are out to make a buck!! I have to admit, those brightly colored fish do make a really pretty picture in those pretty tanks and it is great marketing. And, now, five years down the road, are you going to return your fish??? Nope, you are not, you are going to invest in a larger, more suitable tank, which means more $$$ for the manufacturer. Along the way you are also going to probably be advised to buy this medication or that medication or the other, again, more $$$ to the industry.
Our forum is here to help owners keep their fish healthy and alive. We aren't selling anything, in fact we recommend fresh, clean water over most meds 90% of the time. I am sorry to have to disillusion you with this but, trust me, your fish will appreciate room to breathe and grow!
A regular plastic food storage container, rubbermaid or sterite or the like, can be used until you can find a suitable tank. Are your fish fancies (usually double tails) or commons or comets (fair or feeder fish)? It makes a difference in the size. Two fancies can do well in a 40 gallon tank while two comets or commons will require a minimum of 75 gallons or more.

#8

Tom

6 years ago

They are not fancy, they are 'normal' goldfish I think you would call them.

I have just conducted a 50% water change as that is all I can do tonight (it was two weeks since I last changed water/service kit), but I fear it is too late now.

Thank you for you help and advice.

#9

6 years ago

Yes, those are commons.
He doesn't look good, I must admit. But...they are really pretty hardy fish and those water changes could be a miracle cure. Don't give up quite yet!

#10

6 years ago

You do not need to change the filters every month, that is also a way of getting money from your wallet to their tills.

Get the largest plastic storage tub you can lay your hands on, a large filter and move the fish over as soon as you can. Move the gravel from the orb to the tub as well.

Do at least 2 x 50% water changes a day on the orb until you can get the fish a larger home.

I have enclosed some links for you to have a read.

http://www.myaquariumclub.com/so-you-won-a-carnival-goldfish...-aka-the-very-basics-of-goldfish-care-5613.html

http://www.myaquariumclub.com/a-visual-perspective-on-goldfish-size-4923.html

http://www.myaquariumclub.com/the-complete-goldfish-care-guide-4958.html

#11

Tom

6 years ago

Thank you guys for your help and advice.

Unfortunately the fish did not survive, despite my best efforts.

I will be looking to rehome the remaining fish as quickly as possible (it has become very active and agitated since becoming alone). It does still appear to be in perfect health but I believe you when you say the water is toxic to it and is a ticking time bomb of ill health.

When I can rehome the fish I will then throw away the Biorb as it seems they are not suitable for any fish whatsoever, even tetras.

I am hoping to move into a new house soon. If I decided to keep fish again - I will purchase a large cuboid aquarium for my new home.

#12

6 years ago

Sorry to hear he has gone.

Have a look on internet auction sites for pre used tanks, you get so much more for your money and the fish do not seem to mind 👍

#13

6 years ago

Tom, don't give up on fishkeeping there are some fish suitable to the orb

#14

6 years ago

Tom, I am sorry to hear about your fish, I really had hoped you got to him in time.
I agree with Suesblues, there are some fish species suitable for your biorb. As for rehoming the other goldie a good place to check, especially with Spring coming in many areas, is any local landscaping services. Many of them have clients with outside ponds and needing goldfish.

#15

Tom

6 years ago

Thank you, which fish are suitable and how many?

#16

6 years ago

You can plug in the information into www.aqadvisor.com, and select fish suitable for this sized tank. I used 8 gallon for the tank size since they didn't list anything close in liters. Since they aren't perfect, come back with some you like and we can better advise you.
Also, do a search for "nano fish" using the search bar in the upper right corner and check out some of those.
Finally, I have Endlers and a selection of males only would do fine in there...the males are the colorful ones so would be pretty as well. The females are much larger and they breed lile crazy as do their better known relatives, the guppies so sticking with all males is a good idea.

#17

6 years ago

I must admit male Endlers were the ones I was thinking of, very pretty fish and entertaining, much better than letting the tank go to waste

#18

Dingy80

3 years ago

Tom. There's a lot of advice being given to you on this thread and most of it is way out of line. . The water changes are doing are doing way more harm than good. You are literally shocking your tank of the good bacteria. I've 3 tanks myself. I have a marine, tropical cold water and two biorbs. I've had my fan tail gold and pure black in a 30 litre. They nearly 15 years old. 20%water change every 4 weeks is just fine. Get plenty of living plants too. . They will keep your nitrate level just right.
Sorry to hear about your fish. . I must say though. Like all living creatures fish can also become poorly. As with this case I'm sure it's completely unrelated to your water treatment.

Those may interest you:

#19

Tom

3 years ago

Hi - well a few years on, I have now upgraded to a 60 litre BiOrb. I am also now a very well versed in the science of aquarium water and cycling etc.

The other fish is still very much alive and well, and I added a small 'lemon' goldfish a few months ago. Both are very healthy and the tank and water quality stay crystal clear indefinitely. This has been helped the <email> 'moss balls' I added to the tank.

#20

3 years ago

Dingy80 wrote:

Tom. There's a lot of advice being given to you on this thread and most of it is way out of line. . The water changes are doing are doing way more harm than good. You are literally shocking your tank of the good bacteria. I've 3 tanks myself. I have a marine, tropical cold water and two biorbs. I've had my fan tail gold and pure black in a 30 litre. They nearly 15 years old. 20%water change every 4 weeks is just fine. Get plenty of living plants too. . They will keep your nitrate level just right.
Sorry to hear about your fish. . I must say though. Like all living creatures fish can also become poorly. As with this case I'm sure it's completely unrelated to your water treatment.

Hi there,

thank you for your input onto a thread that is over 3 years old, dates are in the top corner of each post.

If I may, changing water does not Shock the fish nor does it deprive the tank of good bacteria as most is not in the water but in the filter and on the surfaces.

Changing water replenishes the minerals used by the fish as well as removing Nitrates, as Goldfish are huge waste producers, both you and Bob are keeping Goldfish in tanks/bowls that are way too small for them. Single tailed Goldfish can grow to 12 inches in 12 months if in the right conditions.

Please don`t say "I`ve had mine for 15 years in 30 litres" I am one of the people that take in rescues from where the fish have been kept in less than ideal conditions. If your single tailed Goldfish is less than 12 inches long at 2 years old then it is stunted.

I am interested to know the water test results for both of your bio orb bowls for
Ammonia
Nitrite
Nitrate
ph
gh
kh

#21

Tom

3 years ago

I have to assume from the above post that you do not believe goldfish should be kept indoors. A foot-long goldfish would require an incredibly large size indoor aquarium, which 99% of people would or could not keep in their home.

My ammonia levels are virtually zero, I have just run out of the other testing strips, but nitrates/ites were at safe levels. The tank took a huge amount of cycling and vast water changes to reach this stabilised state with only one fish but it has now been there for months. Water is very hard in my area however.

Perhaps you underestimate or are unfamiliar with the capability of the ceramic media within biorbs?

#22

3 years ago

Hi there Tom,

I used to sell biorbs and am fully aware of the filter media. I also have it on good authority, an Oase rep that biorbs of the size you have are not suitable for high bio load fish such as Goldfish.

I also know that a 30 litre or even a 60 litre bowl is not suitable for a fish that can get to 12 inches in length and live for 20 years given the right conditions.

" A foot-long goldfish would require an incredibly large size indoor aquarium, which 99% of people would or could not keep in their home."
Correct, they are advised as a pond fish.

How many goldfish can I keep in a 30 Litre tank?

What fish are best for a 30 Litre tank?

How many small fish can I put in a 30 Litre tank?

How many Litres should a goldfish tank be?