01 Care
Goldfish care
How to keep goldfish healthy, explained from the biology up. Every guide here is written to be read in full, with ranges rather than rules and reasons rather than orders.
A path through the basics
Five guides, in the order that helps most
- Goldfish for beginners What to know before you start, or before you keep going.
- Goldfish tank size The one decision that shapes everything after it.
- Goldfish tank setup Equipment, placement and the first fill, step by step.
- Cycling a goldfish aquarium The invisible part that decides whether the fish thrive.
- How often to feed goldfish Small, frequent, and less than you think.
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. Read it first · 13 minContents
51 guides, written to be read in full.
Getting started 7
- Can goldfish live in a bowl? A goldfish can survive in a bowl for a while. Living well in one is another matter. Here is what goes wrong, why, and the easiest way to fix it. 12 min
- Goldfish tank setup: a step-by-step guide A goldfish tank set up in the right order runs quietly for years. Here is the equipment, where to put it, how to fill it, and what to do before and after the fish arrive. 12 min
- Cycling a goldfish aquarium Cycling grows the bacteria that turn your goldfish's ammonia into something far less harmful. It takes weeks, it is easy to undo by accident, and it is essential to the tank. 17 min
- Goldfish for beginners: what to know before you start Goldfish are easy to keep alive for a while and genuinely rewarding to keep well for decades. This is the difference, explained before you buy anything. 13 min
- What keeping goldfish actually costs A goldfish costs almost nothing and its first year costs at least a hundred times that. Page after page on this site mentions what something costs and none of them adds it up, so this one does — in proportions and arithmetic rather than prices that go stale. 12 min
- A goldfish for a child: what works, and who is actually doing the keeping A goldfish is a reasonable animal to keep with a child and a poor one to hand over to a child. The arrangement that works names an adult as the keeper from the start and gives the child the parts they can genuinely own. 11 min
- A goldfish glossary Goldfish keeping has a vocabulary of its own, from biology, from water chemistry and from centuries of breeders naming what they selected. This is where the words are explained, each with the page that covers it in full, and with the few that are most often misread marked as such. 13 min
Bringing a fish home 4
- What fish can live with goldfish The answer is that goldfish are best kept with goldfish. The list of genuine exceptions is short, and almost every popular suggestion fails on temperature before anything else. 14 min
- How to quarantine a new goldfish Almost every piece of goldfish advice ends with "and quarantine new arrivals", and almost none of it says how. A quarantine tank is a bare box, a seeded sponge filter and at least four weeks of paying attention. 13 min
- Choosing a goldfish and bringing it home Most of what determines how a new goldfish does is decided before it reaches your tank: which shop, which fish, how long the journey, and what you do in the first hour. None of it is difficult and most of it is free. 15 min
- Finding a goldfish no shop stocks Most of the breed pages on this site say some version of you will need a specialist. This is what that means in practice - where uncommon goldfish actually come from, what to ask before paying, what shipping does to a fish, and which breeds are not obtainable at any price. 12 min
Water, space and routine 8
- Goldfish tank size: how big does it really need to be? Bigger than the shop suggests, smaller than some forums insist. Here are the ranges keepers and welfare bodies give, why they differ, and what the standard tank sizes actually suit. 13 min
- How often should you feed goldfish? Small meals, one to three times a day, each about what is gone within a minute or two as a rule of thumb. The rest of this guide explains the exceptions and the reasons behind it. 14 min
- Goldfish water temperature: the right range and why stability matters Goldfish are temperate fish, not tropical ones. They tolerate a very wide range, but warm water shrinks the oxygen margin, large fast changes do harm, and a heater is more often for steadiness than warmth. 16 min
- Do goldfish need a filter? Yes, and it is the least optional piece of equipment you will buy. Here is why, which kinds suit goldfish, how much flow to aim for and how to keep one working for years. 13 min
- How often should you change goldfish water? Most goldfish tanks do well on a 25–50% water change every week. Your nitrate test, not the calendar, tells you where in that range you belong. 14 min
- How many goldfish can I keep in my tank? Goldfish stocking is about waste, not inches of fish. Here is how many fancies or single-tails fit in tanks from 60 to 280 litres, and what else has to be true. 14 min
- Leaving goldfish while you are away A healthy adult goldfish can generally go a few days without food, and up to about a week in a cool room, but vets give that as an emergency limit and not a holiday plan. What it cannot survive is two weeks of a sitter being generous, or a filter that stopped on day three. 14 min
- Handling, netting and moving a goldfish Chasing a goldfish is stressful for it, and injuries often happen during netting. The chase can cost more than the move, and there is a better technique than the net you were sold with the tank. 14 min
Understanding the animal 17
- How long do goldfish live? A well-kept fancy goldfish should live ten to fifteen years, and a single-tail longer still. Most pet goldfish never come close, and the reasons are avoidable. 13 min
- How big do goldfish get? Single-tailed goldfish commonly reach 25–35 cm and fancies 15–20 cm, far larger than most people expect. Here is what decides whether yours gets there. 12 min
- What a healthy goldfish looks like The health section describes more than two dozen things that go wrong. This is the one about what right looks like, because you cannot recognise a change in a fish you have never looked at closely while it was well. 12 min
- Goldfish anatomy and biology Almost every piece of goldfish care makes more sense once you know how the animal is built. This is the reference the rest of the site assumes — what the gills actually do, why there is no stomach, why a fancy floats, and what a thousand years of breeding altered. 16 min
- Goldfish behaviour and intelligence The belief that a goldfish forgets everything in three seconds is wrong, and it is not a harmless error — it is one of the reasons the animal is kept in conditions nothing else would be given. Here is what the fish is actually capable of. 13 min
- The domesticated goldfish Every breed page here describes an animal that does not exist in nature. Goldfish are a domesticated carp, selected for a thousand years by people looking down into bowls, and almost everything odd about them follows from that. 12 min
- How to tell if a goldfish is male or female Outside breeding condition you often cannot tell, and confident answers based on body shape are guesses. In condition it becomes straightforward — which is why the real question is whether your fish are in condition rather than what they look like. 11 min
- Goldfish welfare: what the animal actually needs This site argues for particular ways of keeping goldfish on every page it has. This is the page that says why, in one place — and the reason the argument is needed is that goldfish are tough enough to survive conditions that are bad for them. 12 min
- How to breed goldfish on purpose A spawn is easy to cause and hard to finish. This is the part between deciding to breed and having fish worth keeping — conditioning, the spawning tank, the eggs, and the year after the eggs that nobody warns you about. 14 min
- Wen care for orandas, ranchus and lionheads The hood is the reason people buy these breeds and the thing least often explained. It is normal tissue, it develops over months and years, and almost all of its maintenance is water quality — with a handful of genuine problems that look alarming and a couple of alarming things that are not problems at all. 12 min
- Goldfish genetics: colour, scales and what actually breeds true Goldfish genetics is better understood than it was, and it is not quite what most keepers repeat. A few of the big traits are single recessive genes, others have not been mapped, and what is worth knowing is which traits are stable, which drift with age, and what a spawn from two beautiful parents is likely to look like. 13 min
- Showing goldfish: standards, judging and what the judge is actually looking at A breed standard is a written description of an ideal that no fish fully meets, written by a society rather than handed down. Knowing what judges weigh explains most of what the breed pages describe, including the parts that are uncomfortable. 11 min
- What a goldfish can see, hear and smell A goldfish is a hearing specialist with four-colour vision in bright light, a good chemical sense and a lateral line that reads water movement. Most of what looks like odd behaviour in a tank makes sense once you know which sense it is using. 11 min
- What kind of goldfish do I have? Shop labels are often unreliable and young fish have not grown their distinguishing features yet. Two questions — how many tail fins, and is there a dorsal — sort the breeds into a handful of groups, and usually settle what most changes the care. 15 min
- Photographing your goldfish Photograph it is among the most repeated instructions on this site, and until now no page explained how. The technique for shooting through glass, the two angles that matter, why consistency beats quality, and the real limits of what an image can decide. 11 min
- Koi or goldfish? How to tell them apart, the fish in between, and one pond for both At five centimetres a koi and a goldfish can look alike, and they are not the same animal: one stays a garden fish, the other reaches 75 cm and several kilograms. The mouth tells you which you have, and the answer decides whether the fish needs a tank or a large pond. 12 min
- Stress in goldfish Stress is a response, not a disease: a surge of hormones that readies a fish for an emergency. Brief, it passes. Kept up by poor water, crowding or a bully, it turns down the immune system that holds a tank's everyday infections in check, which is why so much goldfish advice ends at the water. 12 min
When something changes 14
- Aquarium salt for goldfish Salt is often over-used in the hobby and is one of the few additives with real, specific uses. The difference between the two is concentration, purpose, and knowing when to stop. 12 min
- Is my goldfish breeding? Most people meet goldfish breeding by accident and mistake it for illness. The chase looks like bullying, the tubercles look like ich, and the female looks bloated. Here is how to read it and what it asks of you. 13 min
- Why did my goldfish die? Goldfish that die young tend to die of a short list of things, and many of them are about water rather than luck. This page is for working out which one, and for deciding what happens next. 13 min
- Goldfish diseases: what each one actually is The health section is organised by what you can see, because that is what you have. This page is the other half: what the named diseases actually are, how each one works, and why many of them live at low levels in most tanks and take hold when a fish is stressed, while others, such as ich, arrive with a new fish. 16 min
- Using medications safely Many goldfish lost during treatment are lost to the treatment and not to the disease: a dose calculated on a tank's advertised volume, a filter that was never opened, or two medications used in the same week. 13 min
- Finding and working with an aquatic vet Every health page on this site eventually says see a vet, and almost nobody does — because it does not occur to people that a goldfish has that option. It does, and the difference a microscope makes is the difference between treating and guessing. 14 min
- Putting a goldfish to sleep humanely Several pages on this site end at this decision and none of them explains it. Most of the time the answer is not yet, because a common reason people consider it is a problem that turns out to be treatable. When it genuinely is the answer, there is a right way to do it. 13 min
- Is my goldfish bullying the other one? Goldfish have no teeth in their jaws and do not hold territory, so genuine aggression between them is rare. What people see and call bullying is often one of four other things, and each has a different fix. 12 min
- What to do about an injured goldfish A cut on a goldfish is not like a cut on a land animal, because the skin it broke was holding water out. That one fact explains why injuries matter more than they look, why clean water beats every treatment, and why almost everything in the bathroom cupboard is the wrong idea. 12 min
- Rehoming a goldfish you cannot keep Several pages on this site end at 'rehome it' and none of them says how. This is the how — including the real ranking of where goldfish actually go, and the one destination that is never acceptable however convenient it looks. 12 min
- Caring for a goldfish that will not fully recover A goldfish that has stopped improving is not the same as a goldfish that is suffering, and the difference decides everything that follows. Most permanent damage is adapted to within weeks, given a tank that stops asking the fish to do the thing it can no longer do. 11 min
- What heals, what scars, and what never comes back Goldfish heal better than most people expect, and the limits are specific rather than general. Fins regrow from the edge, scales come back without their original finish, slime replaces itself in days, and an eye or a spine does not. 13 min
- Caring for an old goldfish A goldfish that reaches ten has done something most goldfish are never given the chance to do. Old is not ill. The work changes from improving the tank to protecting a fish that has less margin than it used to. 15 min
- What is my goldfish doing? Behaviour, normal and not Most of what worries people about a goldfish's behaviour is normal, and a few things are the earliest sign that something is wrong. Here is how to tell which is which, starting from what you can see. 12 min
Check your own setup