Do goldfish need a big tank?


Do goldfish need a big tank?

Yes! Goldfish do need a big tank – never keep goldfish in a bowl!

It’s important to realize that the goldfish you buy in your local pet shop are very young and have not reached their full size.

You might be surprised to know that common goldfish can reach up to 10″ and fancy goldfish can reach up to 8″, so you definitely need a big tank for them!

Recommended goldfish tank sizes:

Fancy goldfish: 3 feet long and a volume of at least 20 gallons for one goldfish. If you plan to keep more than one goldfish in your tank then add an extra 10 gallons for each additional fish.

Common goldfish: 4 feet long and a volume of at least 30 gallons. If you plan to keep more than one goldfish in your tank then add an extra 12 gallons for each additional fish.

Find out the size of your tank now using our fish tank size calculator!

It’s worth noting that common goldfish are often more suited to a pond once they grow larger in order to ensure that they have enough room to swim around. Very few people have an indoor aquarium large enough to properly keep a fully grown goldfish!

Finally, don’t forget that your goldfish tank needs a filter!

Help I have a goldfish bowl cover

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Even a big tank will get polluted very quickly if it isn’t properly filtered or if you don’t do enough water changes. If possible, get an external filter, as they have a larger volume than internal filters, and sit outside your tank so that they don’t take up valuable space inside your aquarium.

Find out the size of your tank now using our fish tank size calculator!

Read more in our Goldfish Care series.

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  • jignesh

    hello,i have 7 fish in 40 gallon tank i have 2 black moor thier fins not growing like cutting 1 black has curve tail and other is slender and colour losing .help

    • TheGoldfishTank

      Hi jignesh,

      If you mean 7 goldfish in a 40 gallon tank then that is WAY too many. We’d recommend one – two at the very most – for a tank that size.

      With 7 goldfish in a 40 gallon tank, you have no chance of keeping the water quality as good as it needs to be.

      By fins “not growing” and “cutting”, we assume you mean that you’re seeing “fin rot” in your fish. This (and also the loss of color) will be because of the poor water quality.

      You need to either get a new (much bigger) tank, or possibly more realistically, separate tanks for some of your fish.

      If you have friends that are interested in keeping goldfish then it would be worth offering some of your fish to them (as long as they get big enough tanks). Or possibly seeing if the pet store would take them back. Otherwise, some of your fish will inevitably die – and you’ll then have to focus on improving your water quality and properly cycling your tank in order to save the remaining two or three fish.

      While you look for a bigger tank (or tanks), you should do a large water change every day, treating the tap water with a product such as Stress Coat or Seachem Prime.


      • Tiffanystarr Leestarr

        E were at least 200 in thereI have had 5 regular goldfish in a 10 gallon tank for over four years and they have never had the ick or rot or anything and I also only have to change the water about every 2-3 month’s and they seem to still be fine but one of them are significantly larger than the rest of them so I’m going to a 20 gallon but not larger the pet stores should get into trouble if these are supposed to be regulations or something because when we got these goldfish there were so many little goldfish in the tank they couldn’t even swim around I bet ther

        • turboBlue

          Way too many fish in one tank! A minimum 20 gallons is required for just one to live comfortably. They need weekly water changes, NOT once every few months. That is inhumane and you are slowly killing your fish. They will never reach even half of their full potential and are very likely severely stunted. Just because the water looks clean, it’s full of ammonia (fish waste and byproducts), nitrites, and nitrates. Not to mention up to millions of potentially fatal bacteria (too small to see with the naked eye) in every teaspoon of water in your tank! Unhealthy and eventually fatal. You need to upgrade to a 55 now, to start trying to head off some of the stunting and potentially deforming issues that come with overcrowded fish. As they grow, they’ll need a large pond. The goldfish crammed into those tanks at LFS are ‘feeder’ fish for other fish. They’re fed very little (if at all) and usually only live a few days to weeks until they are bought and fed to larger tropical fish for dinner! They are not considered pets and receive terrible treatment. You basically ‘rescued’ them and re-crowded them all over again. The cycle continues because you ‘think’ that this is okay. Really a shame, too. Goldfish are some of the most beautiful creatures on our planet!

  • Aliah Maca-antal

    Hello, I have 10 common goldfish in a 10 gallon tank is that okay?

    • TheGoldfishTank

      Sorry to say this Aliah, but that’s incredibly overstocked! Ten gallons would be on the small side even for one goldfish (we recommend 20 gallons)…

  • Ruth Heinemann Jaeger

    I have 2 common goldfish in a 29 gallon tank. Is that okay?

  • Pingback: Will my fish do okay without a filter for 5 days? | Parenting Answers()

  • jaspuria707

    I have one goldfish in a 15 gallon tank, but he is growing quite large, faster than I thought he would! We won him at the fair 8 months ago and now he is a good 4-5 inches in length. Will I be able to keep him in the 15 gallon tank or would he be better suited for a pond?

  • allauddin

    i want to buy goldfish but my friends says that goldfish die. it want more care than other fish. so what is your advice can i buy goldfish or not?

    • TheGoldfishTank

      Hi allauddin,

      As long as you care for your goldfish properly then there’s no reason why it should be any more likely to die than other fish.

      Getting a big enough tank is particularly important and most goldfish die because their owners keep them in small tanks or even bowls.

      If you have enough room for a 20 gallon tank (or more) then consider a goldfish. If not, it probably would be best to go for a type of fish that requires less room.

      Hope that helps.


  • Liz

    I got given two goldfish and I have no idea what I’m doing (at least I’m honest) I have a ten gallon tank for them, they are tiny (an inch or less each) and beautiful. So in love already. Anyways, I used a dechlorinator drop thing before putting them in the tank like the fish person at Pet Smart said and I’ve been feeding them goldfish flakes three times a day. How should I make sure their water stays healthy? Should I get more drops? I’m on a really strict budget. I see that my tank is too small but that will have to be a problem for later (I’m a poor college student in a tiny one room place and the ten gallon is taking up most of my desk for studying) these goldfish are from a carnival and I just want them to be okay!

    • TheGoldfishTank

      Hi Liz,

      Do you have a filter?

      How often are you changing some of their water?

      As your tank is a bit too small, as you say. it’s important to change the water regularly, install a filter (if you don’t have one already), and it would probably be worth cutting back on feeding.

      You won’t underfeed your goldfish (they really need very little food), but you could risk overfeeding them and polluting their water.


    • turboBlue

      A filter, three 50% water changes a week (at least), one small feeding a day. Skip feeding on Wednesday and Sunday each week. Fasting is actually good for your goldfish and with the overcrowded conditions will help keep water conditions healthy for longer. They will not starve. Healthy goldfish should always look hungry! Later, when you can, upgrade! You’ll need at least a 75 for two commons and a 30 for two fancies. Good luck and happy goldfish keeping!

      • d marino

        2 goldfish in 10 gallons is overcrowding? wow
        So, 3 goldfish need what size tank (little goldfish)?

        • TheGoldfishTank

          We recommend 20 gallons for one fancy goldfish and 30 gallons for one comet/common goldfish.

          Then add an extra 10 gallons for each additional fish.

          So 3 goldfish would need an absolute minimum of 40 gallons.

          Their current size is irrelevant, as they need room to grow.

  • Morgan

    Hello. I am a college student and I have two new goldfish (I believe they’re common goldfish- I got one for free and I purchased another so my fish wouldn’t be lonely, but I only have a two gallon bowl. I can’t have a tank in my dorm and I was wondering if a two gallon bowl would be okay for a while until I’m not in the dorm?

    Also, due to the lack of directions on some of the fish products I purchased, I put a fungus tablet in the tank without either of my fish being sick. Will they be okay or should I change the water asap?

  • d marino

    Can someone give me an idea of just how fast a goldfish will grow? If I purchase a few tiny goldfish and have a 5 gallon tank, how long will that be sufficient before they actually grow much bigger?
    I don’t know anyone that had a goldfish and saw it actually get bigger. (being that they mostly died)

    • TheGoldfishTank

      Sorry to be blunt, but it’s important that we stress this clearly:

      5 gallons is nowhere near enough for even one goldfish for any amount of time.

      It doesn’t matter what size they are.

      You say that you never saw a goldfish get bigger because they died. Yes, that’s because people kept them in tanks that were too small for them.

      It’s like saying that you’ve never seen a dog grow beyond being a puppy… when all the puppies you’ve seen have been crammed five at a time into a tiny kennel.

      We recommend 20 gallons for one fancy goldfish and 30 gallons for one common / comet goldfish.

      Then add an extra 10 gallons for each additional fish.

      • d marino

        Alright then, thanks for that guidance as this makes it clear as to how many = how big the tank! whopee

  • d marino

    I am brand new to gathering goldfish information. Question #1. Can any other species of fish live in a tank with goldfish? If not, why not?
    #2. I would like 2-3 goldfish, so what size tank do they require?
    #3. How long can they stay in a 20 gal before they move into larger surroundings? And then what is the next size required? They seem to be a lot more work than meets the eye.
    #4. Basically, how many years can I expect to keep goldfish in a a 40 gallon before I say goodbye and find them a pond?
    #5. Are all goldfish basically Coi?

  • d marino

    This is an excellent website for goldfish info! Thank you so much and I will be visiting here often.

  • TheGoldfishTank

    Hi Chuck,

    Unfortunately, what an animal needs isn’t dependent on what people can afford.

    We can’t afford an elephant enclosure. So we don’t keep elephants.

    Some people may not be able to afford a large enough tank for goldfish. So they shouldn’t keep goldfish.

    It’s interesting that you say ten gallons is enough to “start” many goldfish. What do you mean by “start”?

    We’re trying to equip people with the equipment and information that they need to keep goldfish that live for several years – and even decades – not just “start” them, whatever that means.


  • Jenna

    I got a goldfish at the store recently and the tank that the person at the store told me to get. It’s like 2 gallons I think.
    I read on here a goldfish needs 20 gallons and I have nowhere near that kind of money so I am not sure what to do with my fish.

  • Mario

    hello, my name is Mario. I have 3 goldfish a common, a comet, and a sarasa. I’ve had them for over a year now in a 10 gallon tank, I do regular partial water changes and try to maintain as happy as possible. they are getting considerably big and I’ve read they need a lot of room, I purchased a 58 gallon tank today, and I was wondering if that will be enough room for them. I was also thinking of adding some rosy barbs now that I have a bigger tank but I’m not sure if that would be too much

  • Sammy

    Can 2 fish live in a 10L tank