The UK's most mis-sold pet. Get it right and a goldfish is a hardy, characterful, surprisingly long-lived companion — get it wrong and it's a short, unhappy life in a bowl.
🔵 Cold-water🐟 Social⏳ 10–20 years🇬🇧 Legal in the UK
Care difficulty
Intermediate
Lifespan
10–20 years
First-year cost
~£285
Min. tank
75L (one fish)
UK legal
Yes
🐠Overview
Goldfish are hardy, social cold-water fish that recognise their owners and can live for well over a decade. There are two broad types: slim, fast common and comet goldfish (which grow large — 20–30cm+ — and really need a pond in time), and rounder fancy goldfish (smaller, but more delicate). They are a genuine commitment, not a fairground prize.
💚 Welfare-honest: goldfish are not bowl fish. A bowl has no room and no filtration. A goldfish needs a filtered tank of 75L+ and can live 10–20 years — longer than many dogs.
🏠Tank & water
Tank size: at least 75L for a single fancy goldfish, plus around 50L for each additional fish. Commons/comets need much more, and eventually a pond.
Filtration: goldfish are messy — a good filter rated above your tank volume is essential.
Cycle first: set the tank up and let the filter mature for a few weeks before adding fish, so beneficial bacteria can handle the waste.
Water care: weekly ~25% water changes; always dechlorinate tap water; test for ammonia (0), nitrite (0) and keep nitrate low.
Temperature: cold-water — no heater needed, but keep it stable (about 18–22°C for fancies).
🥗Diet & feeding
Omnivore — a good-quality sinking pellet plus variety (blanched peas and greens, occasional bloodworm).
Feed small amounts once or twice a day — only what they clear in a couple of minutes.
Don't overfeed: uneaten food pollutes the water fast and is a common cause of illness.
🩺Health & red flags
Most goldfish illness comes back to water quality. See advice if you notice:
Gasping at the surface / clamped fins — usually a water-quality problem; test and do a water change.
White spots (ich) or frayed fins (fin rot) — common, treatable if caught early.
Swim-bladder issues (floating or sinking) — common in fancies, often linked to overfeeding or floating food; try sinking food and soaked peas.
✅Dos & ❌ Don'ts
✅ Do
Use a proper filtered tank (75L+).
Cycle the tank before adding fish.
Do weekly water changes & test the water.
Feed little and often.
❌ Don't
Keep one in a bowl.
Add fish to a brand-new, un-cycled tank.
Overfeed.
Forget that commons need a pond in time.
💷What it really costs
Item
Cost
Tank (75L+) & stand
£70–£120
Filter, net, siphon & test kit
£45–£80
Substrate, plants & décor
£30–£50
The fish
£5–£15
First-year food, treatments & water care
£40–£70
Approx. first-year total
~£285
💡A note on this guide
💡 A second built-out guide alongside the Bearded Dragon — showing the structure copies cleanly across very different animals. Informational only, not a substitute for veterinary advice.