Do Goldfish Need a Heater? NZ Goldfish Care Myths

The quick answer: most goldfish are cold-water fish and don't need a heater in typical NZ indoor conditions — but they absolutely do need a large, filtered tank, not a bowl. The bowl-and-no-filter image is the cause of most early goldfish deaths. Goldfish are big, long-lived, messy fish that need far more room and proper filtration than people expect.

The heater question

• Common goldfish and comets are cold-water fish, comfortable roughly 18–22°C, and generally don't need a heater indoors in New Zealand.
• Fancy goldfish (fantails, orandas, etc.) prefer slightly warmer, very stable temperatures and can struggle in a cold South Island room over winter — a heater set low can help stability.
• The real enemy is rapid temperature swings, not a specific number. Keep the tank away from draughty windows and direct sun.

The myths that kill goldfish

Myth: "A bowl is fine." It isn't. Bowls have no room and no filtration, so waste builds up fast and the fish are stunted and short-lived.

Myth: "Goldfish stay small." They don't — common goldfish can reach 30 cm or more and live well over a decade with proper care. Tank size depends on type: a single fancy goldfish needs around 75 litres or more (and more again per extra fish), while common and comet goldfish grow so large and fast that they really need a very big tank (150+ litres) or an outdoor pond. Whatever the type, over-size the filtration.

Myth: "They only live a year or two." Poorly-kept goldfish die young; well-kept ones often live 10–20 years.

What goldfish actually need

• A large, filtered tank — they're messy and produce a lot of waste, so over-size the filter. See aquarium filter types in NZ.
• A cycled tank before they go in — see how to cycle a new fish tank in NZ.
• Dechlorinated water and regular partial water changes — see aquarium water changes in NZ.
• The right food, not too much — overfeeding fouls the water fast.

Quick takeaways

• Common goldfish are cold-water and usually don't need a heater indoors in NZ.
• Fancy goldfish like warmer, stable temperatures; avoid rapid swings.
• Never keep goldfish in a bowl — they need a large, well-filtered tank.
• Goldfish grow big (20–30 cm) and live 10–20 years when cared for properly.
• Cycle the tank, treat tap water, and don't overfeed.

Shop related categories at PetMall

Looking for a properly sized tank, filter and water conditioner in New Zealand? Browse the PetMall fish range for current options and nationwide delivery.

-> Browse Fish & Aquarium Supplies

Related reading

• How to Set Up a First Aquarium NZ
• How to Cycle a New Fish Tank NZ
• Aquarium Filter Types NZ

References

• SPCA New Zealand, fish welfare, checked 2026-06-05: https://www.spca.nz/advice-and-welfare/
• Companion Animals New Zealand, pet care, checked 2026-06-05: https://www.companionanimals.nz/

Important notice

*General fishkeeping information for NZ owners. Species and varieties differ — research your specific goldfish type's needs.*