Goldfish FAQ: Quick Answers To Everything

Goldfish FAQ written beside 2 goldfish in a tank surrounded by question marks and goldfish faq written in the top right

© / ivosar

There are many questions the average goldfish keeper wants answered, particularly those just starting out and hoping to take the hobby a bit more seriously.

In our section on goldfish care, we have many articles answering the most common questions in-depth, but sometimes a quick answer is all that's wanted or needed.

And that's why we've created this goldfish FAQ.

Please see in the table below a list of the most frequently asked questions on goldfish.

By clicking a question you will be taken directly to a short, sharp answer. And within or after each answer will be links to further articles that answer the question in far more depth should you want it.

We hope you enjoy our goldfish FAQ and if you have a burning question or three that you'd like answered that isn't seen below, please ask in the comments section at the bottom of the page and we promise to reply!


Not All Goldfish Look the Same - How Many Types Are There?

Although it is one species, there are many types of goldfish out there. Some estimate over 300 different varieties.

The most common goldfish fall into one of about a dozen different categories, and those are divided into two types: single tail and double tail.

The most basic difference is exactly what it sounds like: Whether they have one tail or two.

For more info, please read:

How Long Do Goldfish Live? What is the Average Goldfish Lifespan?

If well cared for, your goldfish can be expected to easily live five to ten years.

Many have reported goldfish that live over 30 years, with the oldest on record having lived 43 years!

This is where proper care becomes important. If the poor little fish is kept in a tiny bowl with no filtration, you’ll be lucky to get six months out of it.

Are Goldfish Good For Beginner Fish Keepers?

It's debatable. Yes and no. That wasn't really helpful was it? Let me explain.

Goldfish grow BIG so need lots of room, excellent filtration, and top-notch water quality. They can certainly survive neglectful conditions, but they will thrive much better under the care of a dedicated aquarist.

So although goldfish are hardy creatures, are freshwater and do not need heating (all pluses for a beginner), they do need a large tank, plenty of room and regular water quality maintenance (maybe negatives for a beginner.)

In anyone's opinion, smaller fish are just easier to keep. But don' t be put off, goldfish keeping is not hard, it's just not 'set-and-forget' and needs a little work.

Far too many people buy a little goldfish and a little bowl, only to do some research and realize how much care their new pet needs. Even worse, many don’t do their research at all and end up killing the poor fish.

Are Goldfish Happy in Bowls?

No! Goldfish need a good-sized tank, with plenty of room, a proper filter and more besides.

For more information, please read:

What Size Tank Would You Recommend For a Goldfish?

For fancy goldfish: The rule of thumb is 20 gallons minimum for one fish, plus 10 gallons for each additional fish.

For common / single-tail goldfish: The rule of thumb is 30 gallons for one fish, a further 12 gallons for each additional fish.

You can learn more here:

Do Goldfish Need a Filter?

Quite simply, yes. A goldfish tank MUST have a filter. In fact, all fish tanks should have a filter - and goldfish tanks more than most.

For a discussion of why and what a filter does for goldfish, please see here:

Is a Filter Noisy? Can I Turn it Off at Night?

All filters will make some noise, but a properly maintained one is fairly quiet.

A worn impeller can make a filter noisy, as can air trapped in the intake tube. Also water splashing from the return to the tank can make a sound but to fix this simply add more water.

You cannot turn your filter off at night. It must run 24 hours a day to process tank waste into harmless chemicals.

You can find more details about a noisy filter here:

Do I Need an Air Pump / Air Stone?

Not necessarily. If your filter is causing enough surface agitation, it is providing the same function as the air stone would be.

However, if your goldfish are showing signs there may be a lack of oxygen in the tank, then adding an air stone and bubbles is a good idea.

For more details and help in making the decision, please see our detailed article here:

Can I turn an Air Pump Off at Night?

It’s not recommended.

If you turn it off at night, the oxygen level in the water will drop. Then your goldie could be gasping for air until you turn it back on in the morning. Therefore, leave it running 24/7.

Do Goldfish Need Light? How About Dark?

Yes, goldfish need both light and dark. They are daytime animals just like us, so they need light to see in the day and dark to sleep in at night.

It’s not healthy for them to be left in the dark all day, or for their light to be left on at night.

For a goldfish to be healthy, they need a regular and consistent day / night cycle and that's what you have to try and mimic.

You can find more on lighting your goldfish tank here:

What Temperature Should Goldfish Water Be?

The ideal temperature to keep goldfish at is 65 to 74 degrees F (24 degrees C).

Although goldfish can survive temperatures almost down to freezing (they’ll hibernate) and up to the mid 80s F (30 C) it really is not good for them.

When too cold, their bodies begin to shut down. And the warmer the water the less oxygen it can hold. If your tank gets hot in summer, having an air stone will become more important.

Read more at:

Do Goldfish Need a Heater?

Only if your water temperature regularly dips below 65 deg F (19 deg C) or the temperature in your fish room constantly fluctuates.

A steady water temperature is important, and sudden changes can make your fish sick so if the air temperature in your fish room fluctuates a lot, a heater will help keep it consistent.

If you live in a warm climate where the water will never get too cold, a heater won’t be needed.

What Are the Best Tank Decorations For Goldfish?

Really, anything the goldfish can’t get its mouth around.

Many goldfish keepers prefer a bare bottom tank but decorations are always good as they enhance the fish’s environment and keep them interested.

Driftwood, ceramic decorations, and plastic plants are all excellent decorations. Make sure you are buying your decorations from a reputable store to be sure they will not leech toxins into the water and never use driftwood found on the beach without properly preparing it first for the same reason.

What Are the Best Plants to Put in a Goldfish Tank?

Some live plants will work such as anubias, java fern, valisineria, and amazon swords.

But many live plants will quickly become snacks for your goldies. You will need plants that either grow very fast, are tough enough to stand up to goldfish attacks, or are simply not tasty.

Duckweed spreads very fast, but goldfish love to eat it.

You’ll need to start out with a large amount of it to match a full-grown goldie’s appetite. You also may have problems with your goldfish uprooting your plants as they dig in the substrate.

For more info, please click here: Best plants for Goldfish Tanks and Aquariums

What Were Goldfish Developed From?

Goldfish were bred from Prussian carp (Carassius auratus gibelio) in China about 1,000 years ago. They have since been bred into many different forms and styles.

What Are the Most Common Goldfish Types?

There are many different types of goldfish.

Besides your comets and “common” goldfish, the most commonly seen fancy varieties are fantail, ryukin, ranchu, lionhead, veiltail, bubble-eye, black moor, and shubunkin.

The above are the most common, but there are many more, and more are being developed all the time.

What's the Difference Between a Goldfish and a Koi?

Goldfish and koi are different subspecies of carp. We’ve been keeping goldfish for almost 1,000 years longer than koi.

Goldfish tend to stay smaller and are bred to be seen from the side. Koi belong in a pond, get larger faster, and are bred to be seen from above.

To learn more, click here:

How Big Can Single Tail Goldfish Grow? (Commons, Comets and Shubunkins)

Common single tail goldfish can reach sizes up to 10-12”, not including the tail.

While it can take 5-10 years to get that big, keep in mind the goldie can double in size at the 3 month, 6 month, 1 year and 2 year points. They get big fast!


How Big Can Double Tail Fancy Goldfish Grow? (Ranchus, Ryukins, Moors, Orandas, Celestials)

Most will grow to about 6”, but there are reports of 10-12” double tail goldfish. That’s a monster, but it’s possible.

What Goldfish Types are Suitable For a Tank or Aquarium?

Double tail and fancy goldfish are best for a tank or aquarium. They won’t get too terribly big, and can reasonably be kept in a tank.

Just make sure you’re following the rule: 20 gallons for your first fish, and 10 gallons for each additional fish.

Singles tails 'can' be kept in tanks, though they much prefer a pond. If keeping single tails they need to have much more room to swim. 30 to 40 gallons and a long, flat style tank (not high and deep) so they can really stretch their fins.

What Goldfish Should Really be Kept in a Pond?

Most common single-tail goldfish will get big fast, and they like to swim fast too. So they will be happier in a pond than in a tank. Though if your tank is large enough they can be kept quite happily in a tank.

A common mix-up though is people seeing Koi and thinking they are goldfish. They are not and any kind of koi should definitely be kept in a pond, never in a tank.

Can Single Tail and Double Tail Goldfish Live Together?

It’s possible, but we don’t recommend it.

Single tail goldfish tend to be much stronger swimmers than the double tails, so they will out compete their fancy cousins for food.

If you are keeping single and double tails together, make sure the double tails are getting enough to eat.

What Other Fish Can I Keep in a Tank With Goldfish?

We generally only recommend keeping goldfish with other goldfish.

The problem with other fish is that there are few that enjoy the same water temperatures as goldies. Small fish may get eaten (goldfish will eat anything they can fit in their mouths), and larger more aggressive fish may attack your delicate double tail goldfish.

White Cloud Mountain Minnows often work as tank mates, as do Zebra Danios, Rosy Barbs, plecos and Weather Loach. But your goldies will be most happy with others of their own kind.

For more info, click here:

Do Goldfish Grow to the Size of Their Tank?

No. Goldfish need a proper sized tank to be healthy, minimum 20 gallons for one double tail and 30 gallons for one single tail fish.

The longer answer though is: Yes, they will stop growing when they run out of room. But this is EXTREMELY bad for the fish, and they will die much sooner if kept in a small tank.

For more information, please click here:

What Should I feed My Goldfish?

Goldfish are primarily vegetarians, but they will eat just about anything provided.

Flake food tends to be cheap and not as nutritious, so start with good pellets.

Goldfish will enjoy duckweed, blanched veggies like zucchini or cucumber, and the occasional treat of frozen bloodworms or brine shrimp.

Be sure not to over feed, never more than the fish can eat in a couple of minutes.

For a complete guide on feeding your goldfish, please click here:

How Often Should I feed My Goldfish?

Ideally you should feed your goldfish 3-4 times a day, just a little bit each time. Never more than they can eat in 5-6 minutes (per day, not per feeding).

Goldfish are little pigs, so don’t let them fool you into thinking they need more because they’re begging for food.

Please see our complete guide to feeding your goldfish here:

How Can I Tell if My Goldfish is Sick?

Watch for gasping for air at the surface, heavy breathing, erratic or upside down swimming, refusal to eat, lying on the bottom, or rubbing against decorations or the glass.

Basically, if your goldfish is exhibiting behavior that seems strange or unusual, it might be sick.

How Can I Tell a Male Goldfish From a Female One?

There are a few telltale signs that your goldfish is a boy or girl.

Males have “breeding tubercles” (little white pimples) on their gills during spawning season. Their vent is flat or concave, and they tend to have a more slender body.

Females don’t show the tubercles, have a vent that protrudes (an outie, not an innie), and tend to have a rounder body.

If you have two or more goldfish, the males will chase the females during breeding season. Behavior is often the best indicator.

Read more here:

Is it True Goldfish Only Have a 3 Second Memory?

Not at all! Goldfish are well-known for remembering and recognizing their owners and family.

For more info, read:

How Much Does a Goldfish Cost to Buy? (American Dollars)

Prices for goldfish can range from less than a dollar for a feeder comet at the pet store to hundreds of dollars for fancy or rare specimens.

As a good ballpark figure, expect to pay $5 for a small, juvenile goldfish and up to $30 for a larger adult one.

How Often Does a Goldfish Tank's Water Need Changing?

It's a massive point of contention among the fishkeeping world. Have a quick google search and you will find answers from seemingly authoritative figures, giving very different answers

It's easy to find answers such as 10% a couple of times per week, or 20% weekly, right up to 90% water changes once per week or even more!​

The truth of the matter is you need to perform enough water changes to remove enough nitrates from the water to keep them within acceptable levels. In order to do this, you will need to regularly test the water parameters in your specific tank, for it will vary wildly from one tank to another.

As a general rule of thumb: For basic maintenance of a suitably sized and well filtered tank, that's not overstocked, where the fish aren't overfed and excess food isn't left to rot in the tank uneaten, a good ball-park figure to start with is to change about a third to 40% of your tank’s water once a week.

After testing your water parameters you may find you can scale this value either up or down a notch. But please, do not do huge water changes all in one go as the drastic changes in water chemistry and make up can also stress out and cause harm to your fish.

Note: We will do a write up on the best way to determine how much water to change and how often in the very near future and come back here to link to it when done.​

Click here for more info:

Can We Improve This Goldfish FAQ?

If you have a question you feel should really be included in this goldfish FAQ, a question many others will be interested in, then please let us know and we may add it to the article.

And please, if there's anything you'd like to know, feel free to ask in the comments section below and we will answer every question.

Happy fish keeping!

The History of Goldfish - From Ancestors to Modern Day
Do Goldfish Need Light? And Darkness? How Much Of Each?
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