01 Care guide
The complete goldfish care guide
Goldfish are hardy, long-lived and far more demanding of their water than of anything else. This guide covers what matters, in the order it matters, and links to the detail.
Goldfish have a reputation problem. They are sold as the simplest pet there is, kept in ways that would trouble any fish, and when they die young the conclusion is that goldfish just do not last. The truth is closer to the opposite. A goldfish is a hardy, intelligent, cold-tolerant carp that can live for decades. What it needs is not complicated, but it is not what the pet-shop bowl suggests either. This page is the hub for everything else on the site: read it once for the shape of good care, then follow the links wherever you need more.
If you want the argument behind all of this in one place rather than spread across the site, goldfish welfare sets out what the animal actually needs and why survival is such a poor measure of it.
Start where you actually are
This guide reads top to bottom, and most people arrive part-way through a situation. If one of these is you, start there and come back.
| Your situation | Start here |
|---|---|
| Planning, no fish yet | Keep reading. You are in the best position anyone can be in |
| A fish arrived unexpectedly, in a bowl or a bag | Can goldfish live in a bowl?, then this page |
| Tank set up, fish in it, no idea about cycling | Cycling a goldfish aquarium, today |
| Something is visibly wrong with a fish | The health section, and test the water first |
| Fish is fine, you want to do better | Goldfish welfare and the routine below |
| You have a pond, or want one | Goldfish ponds and building one |
| Working out whether you can afford this | What keeping goldfish costs |
The five things that matter most
Water quality. Goldfish live in their own waste, and the ammonia they excrete through gills and gut is toxic at concentrations you cannot see. Almost every goldfish problem, from clamped fins to sudden death, begins with water. If you only ever learn one skill, learn to test for ammonia, nitrite and nitrate and to act on the results.
Space. Goldfish grow large and produce waste in proportion to their body mass, not their length. A first fancy goldfish needs about 75–100 litres (20–26 US gallons); a first single-tailed goldfish needs 150–200 litres (40–53 US gallons) and will eventually be happiest in a pond. Our tank size guide explains where those numbers come from.
Filtration. A filter is where the bacteria that make ammonia safe live. Without one, you are the filter, and you are only on duty once a day. Read do goldfish need a filter? before buying anything else.
Food. Small amounts, one to three times a day, built on a quality pellet with vegetables and gel or frozen foods for variety. Overfeeding is a common mistake in the hobby, and it harms the fish mainly by ruining the water.
Stability. Goldfish are pond and slow-river fish, where conditions mostly change over days and weeks, not minutes. Steady temperature, steady chemistry and a predictable routine do more for their health than any product.
Choosing a goldfish
Goldfish come in two broad groups, and the choice shapes everything that follows.
Single-tailed goldfish, meaning the common, comet and shubunkin, are the fish of ponds and fairgrounds: streamlined, fast and tough, reaching 25–35 cm (10–14 in) as adults. They tolerate cool water down to about 10 °C (50 °F) and are the better choice if you have a pond or plan one. Indoors, they need a long tank and eventually a lot of it.
Fancy goldfish, such as the fantail, oranda and ranchu, have been bred for rounded bodies and double tails. They stay smaller, typically 15–20 cm (6–8 in), swim more slowly and prefer warmer, steadier water of 18–24 °C (64–75 °F). Their shape brings trade-offs: compressed organs, weaker swimming and more buoyancy problems. They are the better indoor fish, and usually the better choice for a first aquarium.
Keep goldfish with goldfish. Tropical community fish want warmer water, fast fish nip slow fancies, and a fancy with a single-tail for company will lose every race to the food. Whatever you choose, buy from a tank where every fish is active, with clean fins and no white spots, and quarantine new arrivals if you already have fish.
The aquarium
A goldfish aquarium is a rectangle, not a bowl, and its most important measurement is its footprint. Length and width give swimming room and surface area for gas exchange; height mostly gives you a heavier tank to lift.
Anatomy of a goldfish aquarium
- Filter rated well above the tank’s volume, outflow softened for fancies.
- Air stone or surface agitation so oxygen can enter and carbon dioxide leave.
- Sand or bare bottom. Small gravel can be swallowed and lodge in the throat.
- Smooth decor with no sharp edges or gaps a fish could wedge into.
- Hardy plants such as anubias and java fern, attached to rock or wood.
- Thermometer where you can read it daily; avoiding large, fast swings matters more than the exact number.
- Lid and light on a timer for six to eight hours a day.
Start with the biggest tank you can house, because goldfish grow into whatever you give them, and the stocking checker will tell you how many fish it can sensibly hold. Choose a filter rated for more than the tank’s volume: the figure to aim at is a turnover of five to ten times the tank’s volume every hour, so a 100-litre tank wants a filter moving 500 to 1,000 litres per hour. Goldfish produce more waste than the fish most filters are rated for, which is why the box’s tank-size figure is a starting point rather than an answer, and why the filtration guide argues for buying one size up and softening the flow rather than buying small. Use sand, a bare bottom, or stones too large to fit in a goldfish’s mouth, because goldfish sift the bottom constantly and swallow small gravel. Add a lid, a thermometer and water conditioner, and hold off on ornaments until the basics are in place. The tank setup guide walks through the assembly step by step, and the ideal goldfish aquarium shows what a finished setup looks like.
Water and the nitrogen cycle
Everything you do for a goldfish is, in the end, done to its water. The chemistry that matters is called the nitrogen cycle.
The nitrogen cycle
The fish produces ammonia. A first group of bacteria, living mostly on the surfaces inside your filter, converts ammonia to nitrite, which is also toxic. A second group converts nitrite to nitrate, which is far less harmful and is removed by water changes. In a new tank those bacteria do not exist yet, and building them up, a process called cycling, takes several weeks. Read cycling a goldfish aquarium before the fish arrives; it is the step most new keepers skip and the reason so many new goldfish die within the first month.
The targets are simple: ammonia 0, nitrite 0, nitrate ideally under 20 mg/L and comfortably under 40 mg/L, pH between 7.0 and 8.0, and a temperature that does not swing. Tap water must be treated with a conditioner to neutralize chlorine or chloramine, which would otherwise kill the bacteria you have worked to grow. A liquid test kit is more accurate than strips and pays for itself the first time it catches a problem early. Enter your readings into the water parameter checker to see what they mean and what to do next.
The first ninety days
Most of what decides how a goldfish’s life goes is settled in the first three months, and almost all of it before the fish arrives. Here is the whole sequence.
Before anything. Decide the adult size you are keeping — fancy or single-tail, and how many — and cost the tank for that rather than for the fish you would buy today. What keeping goldfish costs sets out the shape; the tank size guide sets out the volume.
Week 1: set it up, with no fish. Tank in position, level, on something that will carry it — the placement page covers what a loaded tank weighs and where it can stand. Substrate, hardscape, filter, heater if the room needs one, lid. Fill with conditioned water. Start the filter and leave it running.
Weeks 1 to 6: cycle it. Add an ammonia source and test daily, watching ammonia rise and fall, then nitrite rise and fall, then nitrate appear. This is the step that decides whether your first fish spends its first month being poisoned, and it is the one most people skip because nothing appears to be happening. Cycling a goldfish aquarium has the method.
Week 6 or so: buy the fish. One or two, not the full stocking. Choose from a shop whose whole system looks well run, which the choosing guide covers, and bring them home properly.
The first fortnight with fish. Test daily. Feed lightly. Expect a small ammonia or nitrite reading as the colony adjusts to a real load, and change water on the readings rather than on the calendar. Watch the fish for a couple of minutes every day and learn what normal looks like for them, which is what the healthy baseline page is for.
Weeks 8 to 12: settle into the routine. Testing drops to weekly. Water changes become the weekly habit. If you are adding more fish, add them one or two at a time with a few weeks between, so the filter can keep up.
And then it is half an hour a week, for years.
Temperature
Named as one of the five things above and worth its own section, because it is the one people either ignore or over-engineer.
The ranges. Single-tailed goldfish do well from about 10 to 24 °C (50–75 °F). Fancies are usually kept at 18 to 24 °C (64–75 °F); that is a keepers’ convention and not a limit, and the reasons given for it, such as cold-sensitive digestion and buoyancy trouble, are experience and not measurement.
The number matters less than the steadiness. A tank sitting at 21 °C all year is better than one swinging between 18 and 24 every few days, and a fish acclimated to slightly imperfect conditions is in a better position than one meeting perfect conditions suddenly.
Most rooms do this without help. A heater earns its place where a room drops several degrees overnight, where a tank sits in a conservatory or a cold hallway, or where the heating goes off for a fortnight. Set as a floor near the bottom of the comfortable range rather than as a target, it does nothing on a warm day and prevents the drop on a cold night.
Above about 27 °C the problem inverts: warm water holds less oxygen while the fish needs more of it. The temperature guide covers both ends and the heaters page covers the hardware.
And if the tank genuinely goes cold — a pond, an unheated room — feeding changes with it, which the seasonal feeding page sets out band by band.
Feeding
Goldfish have no true stomach. Food passes along a long intestine, so they do best on several small meals rather than one large one, and they will keep eating for as long as food is offered. Feed one to three times a day, an amount that disappears within a minute or two, and skip a day each week if you like. A quality pellet makes a good staple; blanched vegetables, gel food and frozen foods add variety and fibre. Many keepers prefer sinking food for fancy goldfish, believing it reduces gulping air at the surface; that is experience and not trial evidence. Our guide to how often to feed goldfish covers juveniles, cold water and a sample weekly routine.
If you take away one thing about feeding, take this: when the water is cloudy or the nitrate is climbing, the answer is nearly always less food, not more filter.
A maintenance routine
Good goldfish care is a small set of habits rather than a series of rescues.
Daily
Look at the fish while they feed. Are they all eating, all active, all holding their fins open? Check the temperature and that the filter is running. Remove any uneaten food.
Weekly
Change 25–50% of the water, more if nitrate is rising, using conditioned water at the same temperature, and siphon waste from the substrate as you go. Test ammonia, nitrite and nitrate; in a mature tank the first two should be zero and the third tells you whether your schedule is keeping up. How often to change goldfish water explains how to read the numbers.
Monthly
Rinse the filter sponges in a bucket of old tank water, never under the tap. Wipe algae from the glass, check that hoses and seals are sound, and look at the fish with fresh eyes for slow changes you might have stopped noticing.
Recognising trouble early
Goldfish hide illness well but hide changes in behaviour badly. A fish that stops eating, hangs at the surface, sits on the bottom, clamps its fins or swims oddly is telling you something, and the first thing to check is always the water. Most “sick” goldfish are reacting to ammonia, nitrite or a temperature swing, and a water change is both the diagnosis and the first treatment.
Physical signs deserve attention too: white spots like grains of salt, red streaks in the fins, a swollen body, cloudy eyes or torn fins. Our health section describes each symptom, its common causes and when a veterinarian is worth consulting; gasping at the surface is the one most people meet first. Keep a simple quarantine tank if you can; it makes treating one fish, and protecting the others, far easier.
If something is wrong, in this order
The site has a page for each thing that goes visibly wrong, and the order you consult them in matters more than which one you land on.
- Test the water. Ammonia, nitrite, nitrate, temperature. This accounts for a very large share of what looks like disease, it is invisible without a kit, and it costs ten minutes — testing goldfish water.
- Change water if anything reads wrong, and keep changing it. This is safe whatever the cause.
- Then look at the fish properly, in good light, and name what you can actually see.
- Then go to that symptom. Not to a treatment.
- And only then consider medicating, which using medications safely argues should be the last step rather than the first.
| What you can see | Where to go |
|---|---|
| White spots like salt grains | White spots |
| Hanging at the surface, mouthing | Gasping at the surface |
| Gills working hard, not surfacing | Fast or laboured breathing |
| Fins held clamped shut | Clamped fins |
| Sitting on the bottom | Sitting on the bottom |
| Floating, tipping or sinking | Floating upside down |
| Swollen body | Swollen abdomen |
| Rubbing against decor | Flashing and rubbing |
| Red streaks in fins | Red streaks |
| A sore or open patch | Ulcers and sores |
| Not eating | Loss of appetite |
| A lump or growth | Lumps, growths and tumours |
| An injury, from something in the tank | First aid |
The full set is in the health section, grouped by what you can see rather than by what causes it — which is the right way round, because you can see the symptom and cannot see the cause.
Lifespan expectations
A fancy goldfish with good care can live 10–15 years, though the Bristol Aquarists’ Society gives 7–10 for the more developed varieties; a single-tailed goldfish 15–20 years, and some live longer. The record, held by a goldfish named Tish in the UK, stands at 43 years. Goldfish that die at two or three have not reached old age; they have usually met one of the problems above. A fish that does reach it needs a little less change and a little more attention, which caring for an old goldfish sets out. The details are in how long do goldfish live?, but the message of this whole guide is the same: clean, stable, spacious water and a modest diet, and a goldfish will be with you for a very long time.
Frequently asked questions
Something looks wrong. What do I check first?
Test the water, before anything else and before buying anything. Ammonia, nitrite, nitrate and temperature account for a very large share of what looks like disease in a goldfish tank, they are invisible without a kit, and every treatment you might reach for works better in clean water and several work worse in poor water. Once the water is ruled out, identify what you can actually see — the health section is organised by symptom for exactly that reason — and only then consider a treatment.
How long before a new goldfish settles in?
A week or two for behaviour, and about three months before the tank itself is genuinely stable. Expect a new fish to be subdued, to hide, and to eat poorly for the first few days; that is normal and it resolves. What matters more is the tank around it, since a filter that has just started is still maturing and the first three months are when most avoidable losses happen. Test weekly through that period even if everything looks fine.
Are goldfish a good first fish?
Yes, with one condition. Goldfish are hardy, personable and forgiving of small mistakes, which makes them a genuinely good first fish. They are not, however, a small or low-maintenance one. A beginner who starts with a tank of 75 litres or more, a filter, a test kit and a cycled tank will find them easy. A beginner who starts with a bowl will not.
What is a common mistake new goldfish keepers make?
Adding the fish before the tank is ready. A new filter has no bacteria, so ammonia builds in the first weeks and the fish suffers before anything looks wrong. Overfeeding is another, and the two compound each other. Cycling the tank first, or testing daily and changing water while it cycles, prevents most of the early losses that give goldfish their undeserved reputation.
How long does it take to set a goldfish tank up properly?
Four to eight weeks before the fish arrives, almost all of it waiting rather than working. The tank itself goes together in an afternoon; what takes the time is cycling — growing the bacterial colony that makes ammonia safe — and that runs on its own schedule. The actual labour is an afternoon of setup, ten minutes a day of testing while it cycles, and then about half an hour a week for the life of the tank.
How much work is a goldfish tank, week to week?
Around half an hour a week plus a couple of minutes a day, once it is established. The half hour is a water change and a test; the couple of minutes is feeding and actually looking at the fish. That is the real subscription, and it is the one tanks fail on — not because anyone decides to stop, but because a half-hour job with no deadline slips a week, then a fortnight, while the nitrate climbs and nothing visibly changes.
What temperature do goldfish need?
Single-tails do well from about 10 to 24 °C and fancies prefer 18 to 24 °C, but the number matters less than the steadiness. Goldfish tolerate a wide range, and large, fast changes do them harm, so a tank that sits at 21 °C all year is better than one that swings between 18 and 24 every few days. Most rooms manage this without a heater; a heater set low as a floor is the answer where a room goes cold at night.
I already have a goldfish in a bowl or small tank. What now?
Improve what you can now rather than waiting until you can do everything. Daily partial water changes with conditioned water hold a fish safely while you sort out a proper tank, and getting the volume and a filter right is the step that changes the outcome. Nothing here is an argument for feeling bad about a starting point that was usually handed to you with no information at all.
Can goldfish live with other fish?
Best with other goldfish. Tropical fish want warmer water, small fish get eaten as the goldfish grows, and fast fish outcompete slow fancies for food or nip their fins. A few cool-water species can work in large tanks, and the compatibility checker lists them, but a tank of goldfish alone is simpler, healthier and more interesting than most people expect.