🏠The Goldfish tank: 100 L, hardware and start-up
Goldfish : Allow 100 L for the first fish and roughly 50 L per additional one, in a tank that is longer than it is tall. Sand or rounded gravel works well, with a lid or hood to limit evaporation.
In short: 20 to 30 cm as an adult, 100 L minimum per fish, cold water at 18 to 22 °C with no heater. Gregarious, curious and greedy, it fares poorly alone and needs companions far more than a solitary bowl. A heavy-waste cold-water fish reaching 20 to 30 cm: oversized filtration, a large volume and regular water changes are non-negotiable.
100 litres minimum: why that number
For a group of 2+ Goldfish reaching 25 cm as an adult, plan 100 real litres — and remember a big tank is more STABLE, hence easier, than a small one: parameters drift slowly, leaving time to correct. This volume suits a sturdy standard cabinet — just verify perfect levelness.
Hardware: filter, heater, lighting
A filter turning the volume over three to five times an hour, no heater needed for this temperate species (18 to 22°C) — a simple thermometer checks stability, and lighting on a timer at 8 to 10 hours a day: any longer and the algae win.
Substrate, plants and start-up
Nutrient substrate under fine sand or quartz, robust plants (anubias, vallisneria, Java moss) and wood to structure the territory. Then patience: a complete nitrogen cycle (3 to 4 weeks, nitrites back to zero) before the first Goldfish — the step every hurried beginner pays for dearly.
Frequently asked questions
What tank size for Goldfishs?
A real 100 litres minimum for a group of 2+ — below that, parameters drift too fast to catch.
Does a Goldfish need a heater?
No: it is a temperate-water species (18 to 22°C) — heating is actually contraindicated. In summer, cooling is the real question.
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