Freshwater Fish · Goldfish

Fancy Goldfish

Carassius auratus

Long-lived coldwater pet, not a bowl fishIntermediate

Lifespan: 10-15+ years
Size: 15-20 cm (6-8 in)
Social needs: Social - keep 2+ together
Time: High (heavy feeding, frequent water changes)
Cost: Medium-High
Diet: Omnivore

Overview

What is this animal?

Fancy Goldfish are the rounded, twin-tailed selectively bred varieties of the goldfish, including fantails, orandas, ryukins, and lionheads.
They are coldwater fish, interactive with their keepers, and routinely live well over a decade when properly housed.

They are among the most mis-sold pets in the hobby, often condemned to bowls or tiny tanks that kill them within months.
Given real space and filtration, they are hardy, characterful, long-term companions.

Temperament

Fancy Goldfish are peaceful, social, and interactive, often learning to recognise and beg from their keeper.
They do best with their own kind and appreciate at least one companion of similar variety and swimming ability.

Do not mix slow fancy types with fast single-tailed goldfish, which outcompete them for food, and avoid tropical community fish, which need warmer water and may nip trailing fins.
A species-only setup of compatible fancies is the safest and most rewarding choice.

A good fit for

Keepers wanting a long-lived, interactive pet
Coldwater (unheated) species setups
Those able to provide a large, well-filtered tank
People committed to 10+ years of care

Common mistakes to avoid

Bowls and undersized tanks (a leading killer)
Overfeeding and floating food causing buoyancy issues
Skipping the cycle / infrequent water changes
Mixing with fast single-tails or tropical fish

Enclosure

Minimum 150 litres (40 US gallons) — for the pair

Cannot be kept alone. The minimum is 2, and the space above is for that group.

Despite their reputation, goldfish need large, well-filtered tanks, not bowls.
Allow at least 150 litres (about 40 gallons) for the first fancy goldfish and roughly 40-75 litres more per additional fish, with powerful filtration to handle their heavy waste.

They are coldwater fish best kept unheated at 18-23C (64-74F), so a heater is usually unnecessary.
Use smooth decor and rounded gravel, avoid sharp objects, and keep nitrate low with large, frequent water changes.
Their bioload, not their size alone, drives the space requirement.

Check your enclosure

Supplies

Setup

Tank and stand
Filter
Heater and thermometer
Substrate, plants and decor
Liquid test kit
Dechlorinator and starter supplies

Ongoing

Sinking goldfish pellets or gel food
Frozen peas (to deshell and blanch)
Courgette and spinach for blanching
Veg clip
Frozen bloodworm or daphnia
Small cup for pre-soaking pellets
Fine net for removing leftovers

Safe substrate: Inert aquarium gravel · Fine, smooth sand · Aquasoil for planted tanks

Work out the cost

Care routine

Daily

Check temperature and equipment
Feed a sinking, pre-soaked food
Head-count and look everyone over

Weekly

Top up evaporationevery 3 days
Clean glass and clear algae
Large water change
Test the water

Monthly

Rinse the filter mediaevery 2 weeks
Trim and thin the plantsevery 2 weeks
Check supplies and reagent dates

Less often

Replace chemical filter media (Carbon/Purigen)every 2 months

Vet: Quarterly water and buoyancy review — every 3 months

Top resources for more info

Independent creators and organisations we would send a friend to. We have no affiliation with any of them, and nothing here is sponsored. Links checked 2026-09-19.

YouTubers

Luke's GoldiesGoldfish keeping indoors and in ponds, from a breeder Girl Talks FishCare how-tos by fish type, tank setup and beginner mistakes Aquarium Co-OpSpecies care guides, filtration and fish health (run by a retailer)

Sites

The Goldfish CouncilInternational goldfish society with care and health resources Seriously FishSpecies profiles with tank size, water parameters and diet for 1,800+ fish Practical FishkeepingLong-running UK fishkeeping magazine with care and species articles

Go deeper

Diet

Fancy Goldfish are omnivores prone to digestive trouble, so diet matters.
Feed a quality sinking goldfish pellet or gel food as the staple, with plenty of plant matter and blanched vegetables, plus occasional frozen bloodworm or daphnia.

Avoid floating flakes and overfeeding, both of which contribute to the swim-bladder and buoyancy problems these round-bodied fish are prone to.
Pre-soaking dry food and offering several small meals reduces gulped air and bloating in deep-bodied varieties.

Health

Selective breeding leaves fancy goldfish prone to swim-bladder disorder, buoyancy problems, and, in some varieties, eye and wen complications.
Most issues are husbandry-driven, with poor water, overfeeding, and dry floating food being the main culprits.

They are very sensitive to ammonia and nitrite, so a fully cycled tank and frequent water changes are essential.
Watch for floating, sinking, or tilting after meals, clamped fins, and flicking, and feed a fibre-rich, sinking diet to prevent common buoyancy issues.

Is your enclosure big enough?

Minimum volume150 litres (40 US gallons)

CompanyCannot be kept alone. The minimum is 2, and the space above is for that group.

Length

Width

Height

Units

Or tank volume

Units

Is this urgent?

In a fish tank the patient is usually the water. Test before you treat — dosing a healthy tank for a disease it does not have makes things worse.

Go now

Any detectable ammonia or nitrite in a stocked tankLarge water change now with dechlorinated, temperature-matched water. Stop feeding. Test again in 12 hours. Both are directly toxic. How toxic the ammonia reading is depends on pH and temperature, so the same number can be harmless or lethal.

Now

Fish gasping at the surface, or crowding the filter outflowIncrease surface agitation immediately, then test the water. Either the oxygen has crashed or the gills are being chemically burned. Both are hours-scale problems.

Now

Sudden deaths, more than one fish in a dayTest ammonia, nitrite, nitrate and temperature before doing anything else. Do not add medication yet. Multiple simultaneous deaths point at the water or the equipment, not at a pathogen.

Now

Today

Flashing — repeatedly scraping against decor or substrateTest the water, then look closely for parasites. Irritation is either chemical or parasitic; the test tells you which before you medicate.

Today

White salt-grain spots over the body and finsBegin the appropriate treatment today and check the temperature. The parasite's life cycle is temperature-driven, and it multiplies with every cycle you wait.

Today

Soon

Clamped fins, hiding, or refusing food for more than two daysTest the water and review recent changes. Usually the earliest visible sign of a parameter drifting.

A few days

Never add a new fish to a tank that is not fully cycled, and never treat blind. A test kit is cheaper than the fish.

This is general guidance for a healthy adult, not a diagnosis. An exotics vet who knows your animal always overrides it — and the time to find one is before you need one.

What it really costs

Setup, monthly, first year and across a whole life, itemised and with the electricity worked out from the actual wattage. Published figures for the same animal disagree by a factor of four, so the calculator shows ranges rather than picking one.

Region

How many animals

Your electricity price, per kWh

Buying the setup

Bedding and substrate

Substrate in an aquarium is a filter as much as a floor. Most of the biology lives in and on it.

Safe

Inert aquarium gravelRinse thoroughly before use. Grain size should be too large to swallow and too small to trap food.

safe

Fine, smooth sandCorrect for corydoras, kuhli loaches and anything that sifts. Their barbels wear away on sharp gravel.

safe

Aquasoil for planted tanksExcellent for plants, but it leaches ammonia for the first weeks. Cycle around it; do not stock into it.

safe

Bare bottomLegitimate for quarantine and grow-out tanks. Easy to clean, but it holds far less biological filtration.

safe

With a caveat

Crushed coral or aragoniteDeliberately raises hardness and pH. Correct for rift-lake cichlids, wrong for soft-water species.

with a caveat

Very deep sand bedsAnaerobic pockets form below about 5 cm in still sand. Either keep it shallow or keep it stirred.

with a caveat

Painted or coated gravelUsually fine, but coatings chip. Test a handful in a jar for a week first.

with a caveat

Never

Sharp or angular gravel with bottom-dwellersWears down barbels and leads to infection in corydoras and loaches.

never

Anything containing metal, limestone of unknown origin, or shells in a soft-water tankSlowly alters chemistry in ways that are hard to diagnose later.

never

This is our general list for freshwater fish. We have not built one specific to Goldfish yet.

My kit says 0.25 ppm. Is that dangerous?

A liquid kit measures total ammonia, but only the un-ionised fraction is really toxic, and that fraction is governed by pH and temperature — each whole pH unit multiplies it roughly tenfold. So the same reading can be nearly harmless in one tank and lethal in another; this works out which one you are in.

Total ammonia, ppm

Temperature, C