Freshwater Fish

Goldfish Fish: Care Guide

We present the beginner’s guide to the basic care of goldfish. We show you step by step the fundamental knowledge to successfully care for your goldfish.

Goldfish are one of the most common, popular, cheap and easy to care for fish out there. And they make great pets for both aquarium enthusiasts and beginners to this wonderful aquarium hobby.

If you’re a somewhat overwhelmed beginner and want someone to show you how to care for a golden carp, you’ll love this goldfish care guide.

Thanks to this goldfish care guide you will be able to start setting up your aquarium, and we will guide you through the basic steps you need to take care of your goldfish.

Keep reading and discover all the details on how to take care of a goldfish, below.


They are related to but not the same as carp, and were first domesticated from food fish in China more than 1,000 years ago. If you want to have more information about fish you can take a look at our category dedicated to our aquatic friends.

Goldfish, goldfish, goldfish , or goldfish are distinguished from koi and common carp by the absence of barbels or «whiskers» at the corners of their mouths.

Through selective breeding, many varieties of goldfish are now available, and when cared for properly, goldfish can live for more than 20 years in captivity.

Natural Habitat of Goldfish

Goldfish are cold freshwater fish that are widespread throughout nature and can be found in rivers, streams, lakes, ponds, reservoirs, and virtually every freshwater habitat on the planet, from temperate to tropical environments.

Goldfish have also been introduced to many parts of the world to control mosquito populations.

Types of goldfish

There are many types of goldfish, the common goldfish, comet, shubunkin, oranda, ryukin, Lionhead, Telescope … to name a few.

Most goldfish fall into one of two categories: regular or fancy. Regular fish are comets, commons, and shubunkins. There are many more varieties of fancy goldfish.

If you can choose, it is recommended to choose the common goldfish because the characteristics of the fancy fish provide internal organ problems as a result of their deformities.

However, if you already have some other type of goldfish, then you can take advantage of the fact that they do not grow as much as the common ones, so they do not need such a large tank when they are adults.

When choosing multiple goldfish, do not mix varieties with the common ones, as the common ones will outcompete the other varieties for food.

The differences between Common Carassius Auratus and the other varieties is that Common Carassius Auratus are generally larger, faster, more active, need larger tanks, and are generally healthier.

Goldfish in captivity

Common goldfish, kites, and shubunkins make excellent outdoor pond fish and have been known to survive relatively cold winters.

Fancy goldfish, such as orandas, ryukins, and others, can also be kept in outdoor ponds, but they are more vulnerable to predators and must be protected over winter in harsh climates.

In an aquarium, goldfish need minimum conditions that we will now see in more detail.

Goldfish Care Guide

Choose your new golden carp

It is best to start off on the best foot possible by buying a goldfish that is obviously not sick. If you have already bought it or you have your goldfish, then you can skip this step and go to the next point.

If you are buying from your local pet store, you will need to look for fish that meet the following criteria:

  • Swims actively and normally, without floating or sinking problems.
  • He looks cheerful and constantly on the go, trying to find something to eat.
  • It does not have severe genetic defects.
  • It is not in the same tank with sick or dead fish.
  • You are not living in dirty water conditions that could lead to infection.
  • Shows no obvious signs of disease: bloody-looking fins, white spots, red markings, etc.

But there is something else to watch out for…

The type of goldfish you buy can make a big difference in the size of the tank you’ll need for it to grow to its full potential.

Slender-bodied goldfish such as the Common, Comet, and Shubunkin are small when young, but can grow to around 30 cm. This is why they are normally kept in ponds.

So if you’re short on space, a fancy goldfish is probably best for you. Fancy goldfish have two tails and a shorter body, and they don’t get as big, so they don’t require as much space.

Once you’ve chosen your new finned friend, it’s time to take them home and quarantine them.


Two reasons to keep your new friends in quarantine:

  • Quarantine gives the new fish a period of time to «rest» in a separate area before being introduced with your other fish. If you don’t have any other fish, you don’t have to do it in a separate tank.

    The immune system will be very low at this time, making them prone to disease. Using a quarantine aquarium, we will prevent them from being affected by the fish that are already there, while the new ones are stressed after the transfer.

  • Quarantine allows you to treat all the common Goldfish diseases that your fish might have, thus helping to prevent them from getting sick later. If your supplier has already fully quarantined their fish, then you don’t have to treat all diseases.

This is a sad reality:

Nearly all pet store goldfish are already sick or bordering on sick.

Pet stores cannot afford to quarantine each shipment of fish for weeks and treat them for the myriad of diseases they can carry before they are released for sale.

They may look good when you buy them, but they have been through a long journey and are very stressed when they arrive at their final destination. By the time they get home, they are nearly exhausted and harbor a host of pathogens invisible to the naked eye.

These pathogens may not cause any problems at first, but as they multiply, the fish eventually succumb.

That is why it is so common to hear: “My goldfish always end up dying”.

To recap, if you buy your fish from a pet store, you are going to need to treat your new fish yourself. And if you already have fish, you’re going to need a separate tank to do this, so your new fish don’t contaminate the others.

How to set up your first gold carp aquarium

If you are wondering if the typical ball-shaped fish tank can be used, the answer is NO.

Goldfish should never be put into small aquariums or any other unfiltered container. In addition to having a relatively high oxygen demand, fish waste can be harmful if allowed to accumulate. Here you have the post about the Goldfish Air Pump in which we talk about whether this accessory is necessary in a goldfish tank.

And our advice is that you take a look at our aquarium guide for beginners, with which you will quickly understand why you should not use this type of fish tank.

Common goldfish are actually one of the largest species and can grow up to 18 inches in length.

A good premise would be to try to pick the biggest tank you can afford. Think that a bigger tank equals healthier fish, and healthier fish equals a happier aquarist.

So how big does the aquarium have to be?

That will depend on the goldfish and how many you want to have in your tank. We have already seen that there are two main types of goldfish, the common ones and the fancy ones.

Common goldfish varieties grow so large that they need 150 liters for the first fish, 75 for each additional one.

Yes, as hard as it may seem to believe, they start out so small and end up so big.

Now, fancy goldfish can reach 15 to 20 cm, so 35 to 70 liters per fish is enough. Their size makes them much more suitable for indoor aquariums.

And where do I put the tank?

On the other hand, you will have to choose where to place the aquarium, and it is important to consider all aspects.

First, is there air conditioning or heat sources nearby? Do not place the aquarium in a place where temperatures change sharply.

You’ll also want to keep your tank away from windows, as sunlight filtering into the tank can cause algae growth if there’s too much light, plus windows are often drafty.

If you have no choice but to place your tank in direct sunlight, use a cover that provides shade to reduce the amount of ambient sunlight.

If you have small children and/or pets, especially cats, find a place that is out of their reach.

Substrate, plants and decoration

Some are happy with a “Sunken Pirate Ship” and some fake plants, and others prefer a natural plant aquascaping with woods and rocks.

At the bottom of the tank, we have the substrate. Pea-sized gravel is not a good choice because goldfish naturally sift through the substrate in their natural habitat and can choke on it.

Since we can’t use pea-sized gravel, we’re left with two more options: specialized aquarium sand or large river rocks, both with their own pros and cons, but no choking risk for goldfish.

Then we have the aquarium plants. When choosing natural plants, remember that goldfish naturally pull up plants, so you’ll need to choose hardy and/or fast-growing plants, or your plants will last a whirl.

When you buy your plants, it is recommended to quarantine them in an empty jar for 1-2 weeks, even if they are sold as pest and disease free. If you have no experience with live plants, we recommend our guide to aquarium plants for beginners.

If you don’t want live plants, another option is fake plants. Fake plants are good because they require no maintenance except for occasional algae cleaning. However, fake plants lack one of the best qualities of live plants: they don’t clean or purify water.

Once you have your plants, natural or not, you can choose some decorations so that the goldfish have some shelter. Regular plastic ones are great because they provide hiding places for your goldfish and they don’t change the pH of the water like wood does.

When you are choosing decorations, do not choose any with sharp edges, or that are irregular because your goldfish could be injured by them. Remember, goldfish will always feel more comfortable and less stressed, making them less prone to disease, in a natural-looking environment.

And what else do I need?

But you will need more accessories than a tank to have a happy goldfish…

  • Aquarium water filters provide a place for beneficial bacteria to grow that keep the water quality in good shape for longer.

    Beneficial bacteria are the ones that help keep the water healthy. However, you will need to do water changes even if you have a filter. The filter must be slightly oversized to deal with a high production of residues.

  • For water changes, you will need an aquarium siphon. The type of siphon that connects to the sink is ideal for tanks of more than 70 liters and will save you a lot of back pain by avoiding the transport of buckets. No matter how big your filter is, you will always need to do a few water changes.

  • An aquarium heater like the one you can see if you click here to maintain a constant temperature, preventing alterations that can stress the fish. Especially recommended for fancy goldfish.

  • An LED aquarium light will keep your fish and plants exuberant, while also allowing you to enjoy looking at them.

Prepare the aquarium water

When it comes to providing freshwater aquarium water, tap water needs to be treated with the proper conditioners.

It is important that you never put untreated tap water in your aquarium, as this water contains chemicals that can kill your fish.

Add the right water conditioners

Seachem Prime is recommended by many because it also reduces ammonia and nitrite toxicity for 48 hours, two parameters that are very prevalent in new aquariums.

But even once you add your water conditioner, there’s still something else you need to know… The aquarium isn’t quite ready to add your new goldfish yet.

At this point, many people wait 20 minutes or 24 hours, depending on what the pet store clerk told them, and then add their goldfish.

Who wants to wait, right?

But in a week or so, the fish will be seriously ill, even dead.

This is because you haven’t cycled the tank first…and also not done enough water changes to make up for the lack of an established filter.

Goldfish produce waste that quickly becomes toxic to them. Only two things can be done to eliminate them: water changes or having a good colony of friendly bacteria.

Beneficial bacteria can help convert this waste into non-toxic forms through a process called the Nitrogen Cycle.

Aquarium cycling

The process called aquarium cycling is based on the nitrogen cycle and has to be done before adding any fish to form a colony of beneficial bacteria.

If you already have the fish, it’s too late to go through this process.

You will need to do very frequent water changes and add a bacteria culture starter to speed up the process, at least every other day for a few weeks until the colony establishes itself in the filter.

If you don’t have the fish already, you will have to cycle your aquarium, and in this article we explain how to cycle an aquarium step by step, so you don’t miss a single detail.

But keep in mind that a set filter will never do ALL the work for you, it will help you narrow it down.

Now that you know how to make your aquarium water safe for your new pet, it’s time to add to the fish.

Water temperature

Goldfish prefer cold water, but can also be kept in aquariums with slightly warmer water.

The ideal water temperature for common goldfish is between 18 and 20 ºC. While the ideal water temperature for Fancy goldfish is between 18 and 22 ºC. Comets and shubunkins can survive in water as cold as 15°C.

Keep a submersible heater and thermometer in the tank to ensure water temperatures remain stable within the correct range.

Place the thermometer in the tank opposite the heater.

When choosing a heater, always make sure it is suitable for the size of your aquarium. If you have doubts in this regard, we invite you to take a look at our guide for beginners on the aquarium heater, where we tell you everything you need to know about this accessory.

Some aquarists choose to put their goldfish in the same tank as tropical fish. This is not recommended and each specific case must be studied.

Some tropical fish have temperature and feeding requirements that are similar to a goldfish, but would still require the goldfish to live in a warmer water temperature than recommended.

Behavior and compatibility of goldfish

If housed without a heater, they should be kept together with other fish that tolerate cooler water temperatures. They are gregarious, which means that they like to be together.

They are intelligent, have a good memory and can be very tame. They can be taught to hand feed and interact with their owners. They can also distinguish their owners from other human beings.

Goldfish of different sizes can be kept together, however, commons, kites, and shubunkins can become too boisterous for smaller goldfish as they grow, and may need to be separated.

Always consult an aquarium expert before adding new fish to your aquarium.

Acclimate goldfish to the aquarium

The acclimatization method that we are going to discuss here is the flotation acclimatization method.

  • Float the bag that the fish come in in the water for 20 minutes to acclimate to temperature.
  • Open the top of the bag, without letting any water in. Every 5 minutes, add about a little aquarium water to the bag. Repeat this for 30 minutes.
  • When the time has passed, with clean hands or a net, gently pick up the fish and transfer them to the aquarium. But be careful not to pour the water from the bag into the tank.

It is done!

New fish may be a little scared for a while, and it is common for them to hide on the bottom until they adjust to their new environment.

If your fish have been shipped recently, you’d better not feed them for 24 hours. Once you start feeding them, do so very sparingly to avoid causing water quality problems.

There is another method of acclimatization that involves dripping the water from the tank, and it is better for the fish than the float acclimation method. But it requires a way to slowly drip the water from the tank into the new water. We will leave it for another article.

How to properly feed goldfish

First of all, goldfish obviously need food at regular intervals to survive.

In the wild, golden carp are omnivorous, feeding on aquatic plants, fish eggs, insect larvae, crustaceans, and even other smaller fish.

As pets, goldfish remain omnivorous, but the menu changes slightly.

But the most important thing is that the amount of food they consume directly affects the quality of the water and therefore the fish themselves.

A healthy diet equals healthy fish.

Overfeeding is a serious problem that ends up causing the death of many goldfish. And this is not easy because fish love to eat.

What can goldfish eat?

Goldfish feed contains less protein and more carbohydrates than other fish feeds. For this reason, goldfish should not be fed a beet food.

Goldfish will consume these betta foods, but they won’t have the nutrients they need. Also, it is also not recommended to feed a goldfish human food such as bread, crackers, crumbs, rice or potatoes.

It is advisable to use fish food formulated specifically for goldfish. However, some goldfish foods are better than others.

Gel food is the best food for goldfish

I’m going to start by quickly telling you why I don’t recommend flake food:

  • It falls apart when falling into the water.
  • It’s hard to know exactly how much you’re feeding.
  • It floats, so your goldfish could inhale air when feeding, causing digestive problems.
  • They lose some of their nutritional value once the can is opened and exposed to air.
  • It is common for companies to use filler ingredients.
  • We know that a balanced diet between high quality goldfish foods and vegetables is key. But which commercial goldfish foods and vegetables are best?

Here’s what you need to know, especially if you have a Fancy Goldfish:

Let’s go back to nature. Here, everything the goldfish consume is generally soft and moist, so their digestive system has evolved to process these foods.

But not only that.

Goldfish do not have a stomach, which means that different parts of their intestines do the work of breaking down food and absorbing nutrients. The result? Food cannot be stored for long and is processed much faster.

Because of this, soft, moist foods are easy for goldfish to digest. Which brings me to the best type of goldfish food: gel food.

If you want to know more about gel food for goldfish, we have an article dedicated to this topic.

Flakes or flakes

For example, commercial flakes, as soon as they hit the water, the flakes begin to leach their ingredients, which can lead to water quality problems.

The fish also end up taking in a lot of air when eating them. Goldfish are natural bottom feeders, and can gulp air when surface feeding, causing them to lose their balance and float upside down.

To prevent this, soak flake foods briefly before feeding and avoid using floating pellets.


The pellets provide all the nutrients that goldfish need. The best ones have a lot of protein, fat and very little fiber. The type of pellets that sink are ideal.

Make sure your goldfish is big enough to swallow the pellets.

And keep in mind that the flakes start to lose nutritional value as soon as you open the package, while the pellets maintain their nutritional value much better.

How often do I feed the golden crucian carp?

It’s best, however, to provide your fish with an automatic fish feeder like this one you can see here or a feed block if you’re planning on going away for a period of time.

As we said before, it is also important not to overfeed the fish. A small pinch of food once or twice a day is usually enough, but it depends on the number of fish.

For best results, feed them only what they can consume in 2-3 minutes, once or twice a day. Any food that is not eaten will sink to the bottom of the tank, decompose and contaminate the water.

Goldfish’s metabolism slows and speeds up based on water temperature, so if the water is «on the cold side,» the fish may not even need to eat that often.

If you want to know more about feeding goldfish, you can visit our guide dedicated to how to feed goldfish correctly.

Goldfish Care

Just like cats need their litter boxes changed, fish need their water changed on a regular basis.

If you have a large aquarium equipped with a water filter like this, you will probably need to change the water and clean the tank every two to four weeks or so. Of course, if you notice algae or contaminants in the water, you should clean it first.

Water changes to have a healthy fish

That substance will build up until it starts to harm your goldfish.

The solution? Regularly replace a percentage of the tank water with fresh, clean water.

The two most common mistakes people make when doing water changes are: not using dechlorinated water at the correct temperature, and removing goldfish from the tank to do a 100% water change.

To do the water changes, get an aquarium siphon to remove the water from the aquarium. Now exactly how much and how often depends on several factors: the stocking density of your aquarium, the amount of food you feed your fish and the results of the water tests.

Roughly we can estimate 30-40% of the aquarium water, while keeping the goldfish in the aquarium, because they will be much less stressed than if we take them out.

Water changes should be done every one to two weeks, though keep in mind that if nitrate levels are above 30, you may not be changing enough water often enough.

Monitor the behavior of your fish

Fortunately, seeing the Goldfish is fun and enjoyable, which is why we have them at home, after all.

Whenever you notice a change in his appearance or behavior, do a water change.

Not a day should go by where they don’t check themselves, because sometimes a lot can change in a short period of time.

Aquarium cleaning

The key is to never use soap or detergents to clean the tank and its decoration. When cleaning your aquarium, always remove any decorations and rinse them well under warm tap water.

Try not to remove the fish from the tank while cleaning it if possible, as environmental changes can stress the fish and make them sick.

Clean the glass with an aquarium cleaning tool like this one and use a gravel vac or siphon to clean the gravel or substrate.

When using a gravel vac, stop once the water level in the tank has dropped about a third. It should give you enough time to clean most of the gravel and the tank. You can finish cleaning the rest of the gravel in the next cleaning.

When you change the water, make sure that the temperature is the same as that of the aquarium before refilling it.

Water analysis to check critical parameters

Poor water quality is the main killer of aquarium fish, but the problem is that the water can look very good. It doesn’t have to look cloudy or unsightly to be extremely toxic to your fish.

Additionally, sudden changes in water temperature or chemistry can be harmful, even fatal, to goldfish.

That’s why we use test kits. Water test kits are the only way to know what is going on with your water.

After adding the fish, the quality of the water changes over time. By regularly testing your water, we make sure nothing gets out of control before it’s too late.

It is recommended to test the water every week in an established aquarium, that is, one that is more than a month old and has been cycled.

The most important levels to check are ammonia, nitrite, nitrate, pH, KH, and GH levels to ensure they are within recommended ranges.

The pH is not critical, but should ideally be between 7.0 and 8.4.

In fact:

It is a good idea to check the pH every day. This is because the pH can suddenly drop without warning, leaving your tank in a shambles.

It is advisable to use a pH and/or ammonia alert like this one in the aquarium to keep it under control without having to test the water daily. All you have to do is watch it when it is fed to the fish.

Reproduction of goldfish

Eggs can be seen attached to plants and other decorations. To prevent the eggs from being eaten by adults or other aquarium fish, plants and other objects to which they are attached can be moved to a separate aquarium where they will hatch in 48 to 72 hours.

Identify and treat diseases

It can also happen if a new fish is added without quarantining it, infecting the others.

It can even happen for no apparent reason. Often this happens because the fish brought something with it.

Dealing with disease is something that most aquarium enthusiasts have to deal with at some point.

Although it’s not fun, it’s part of the hobby. But there is good news:

The earlier the problem is discovered, the greater the chance that things can be changed. Being able to detect when there is something different about the fish will greatly affect the prognosis.

We will soon publish different posts dedicated to goldfish diseases to provide more information on abnormal symptoms to look for. To begin with, we have the post dedicated to dropsy in goldfish, unfortunately a common disease for our aquatic friends.

Final conclusions

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