Goldfish: gear and buying guides
The goldfish is a social, greedy cyprinid that easily reaches 20 to 30 cm as an adult, a far cry from the fishbowl cliché. It lives in unheated cold water and requires at least 100 L for a single fish, ideally much more since it should be kept in groups. As a heavy waste producer, it calls for oversized filtration and regular water changes.
Profile : 20 to 30 cm as an adult, 100 L minimum per fish, cold water at 18 to 22 °C with no heater.
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Species profile
- Lifespan
- 15 to 30 years
- Adult size
- 25 cm
- Minimum tank
- 100 L
- Water temperature
- 18 to 22 °C
- pH
- 7 to 8
- Temperament
- Gregarious, curious and greedy, it fares poorly alone and needs companions far more than a solitary bowl.
- Health watch
- dropsy favored by heavily loaded water · swim bladder disorders worsened by overfeeding
🩺 Reminder: this page informs, it does not diagnose. For any symptom or health question, your veterinarian remains the only reference.
Goldfish gear, family by family
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Food
A big-appetite omnivore: sinking cold-water pellets, supplemented with blanched vegetables and frozen foods. Split meals into small portions to limit digestive issues and water pollution.
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Care & grooming
Goldfish produce a lot of waste: plan a filter turning over 4 to 5 times the tank volume per hour and a 20 to 30 percent water change every week. Monitor nitrites and nitrates with regular test kits.
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Toys & enrichment
Choose sturdy plants such as anubias or vallisneria, as goldfish uproot and nibble everything. Smooth driftwood and rounded stones provide exploration areas without damaging their fins.
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Bedding & habitat
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.
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Travel & safety
Transport it in a bag filled one-third with water and two-thirds with air, secured in an insulated cooler. Then acclimate for 20 to 30 minutes to equalize temperature before releasing it without the bag water.
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Accessories
A powerful external filter, a wide net and a gravel vacuum are essential; a heater is unnecessary. Expect an initial equipment budget of around 150 to 300 euros for a 100 to 200 L tank.
🍖 Feeding a Goldfish: omnivore diet, frequency, mistakes
Feeding a Goldfish: diet and habits
The Goldfish is an omnivore: a quality staple (flakes or granules) varied with frozen foods and greens. Since it eats throughout the water column, pick a floating and sinking mix and stop at what gets eaten in two minutes: beyond that you are feeding the water, not the fish.
Frequency and variety
The adult Goldfish rhythm: one or two micro-feeds daily plus one weekly fasting day, perfectly tolerated — remember that overfeeding is the top cause of degraded water. In a group of 2 or more, check everyone reaches the food: dominants serve themselves first. Alternate dry, frozen and rinsed thawed prey across the week.
The costly mistakes
The Goldfish “begging” at the glass is not starving — it has simply learnt your silhouette: hold the two-minute line. Bottom-shelf food disintegrates before it is eaten and loads the water; the price gap to a reliable brand is measured in euros per year. The rest of the profile is on the full Goldfish profile.
Quick answers
- How often should a Goldfish be fed?
- One or two small daily feeds eaten within two minutes, plus one fasting day a week. In doubt, underfeed: the water will thank you.
- What food suits a Goldfish?
- An omnivore: a quality staple (flakes or granules) varied with frozen foods and greens — served in a form matched to its swimming zone.
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🧴 Water care for a Goldfish: 18 to 22°C, pH 7 to 8
The Goldfish’s water: its real parameters
The Goldfish’s water contract has four clauses: 18 to 22°C, pH between 7 to 8, zero detectable nitrite, nitrates capped at 25 mg/L. A drop-test kit (NO2, NO3, GH, KH, pH) beats any strip — and the nitrogen cycle, three to four weeks before any fish, is non-negotiable.
Water changes and tank upkeep
10 to 20% of the volume weekly, with water near tank temperature — easy for this temperate species, gentle substrate siphoning as you go and filter media rinsed in tank water, never under the tap: chlorine sterilises your filter.
Health: what stalks the Goldfish
Known watch-points: dropsy favored by heavily loaded water and swim bladder disorders worsened by overfeeding. Nearly every aquarium disease stems from degraded water or chronic stress: test the water BEFORE treating — medicine poured into loaded water makes everything worse. Well kept, a Goldfish lives 15 to 30 years.
Quick answers
- What water parameters for a Goldfish?
- 18 to 22°C, pH 7 to 8, zero nitrites and nitrates under 25 mg/L — checked with drop tests, not by eye.
- How often should a Goldfish tank get water changes?
- 10 to 20% weekly, water brought to temperature, filter rinsed only in tank water. Consistency beats volume.
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🏠 The Goldfish tank: 100 L, hardware and start-up
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.
Quick answers
- 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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🧰 Accessories for a Goldfish: tests, upkeep and budget
Water tests: your dashboard
Before any decor, equip the Goldfish tank with a drop-test kit (€15-30): nitrites and nitrates weekly, hardness and pH whenever doubt creeps in. Then come the net sized for 25 cm, the substrate siphon and the dedicated bucket — never the cleaning one, whose detergent traces contaminate the water.
The Goldfish specifics
a reliable thermometer and, in summer, a surface fan — heat is its real risk; a battery backup air pump: at full stocking, a filtration failure is measured in hours.
The full budget, no surprises
An equipped 100 L setup (tank, filter, lighting, substrate, decor, tests): expect €200 to 450 upfront, then €10 to 25 a month (food, electricity, conditioner). Second-hand often halves the tank price — only the filter and heater deserve to be new. Details on the full Goldfish profile.
Quick answers
- Which accessories are essential for a Goldfish tank?
- Drop tests, siphon, net, dedicated bucket, thermometer and summer cooling: the whole kit stays under €60.
- What budget for keeping a Goldfish?
- €200 to 450 to set up an equipped 100 L tank, then €10 to 25 a month in routine costs.
See it in the Planète Pets shop: Stick-on digital thermometer for aquarium and terrarium glass (€18.90) · the whole shop
We don’t ship products to your country yet; our practical guide downloads anywhere: Beginner axolotl: aquarium and care (€19)
Guides to read
- Community aquarium or species-only tank: which is right for a first setup?Bedding & habitat
Community aquarium or species-only tank: pros, cohabitation risks and advice for choosing how to set up your first aquarium.
- Best easy aquarium plants without CO2 for beginnersToys & enrichment
Which aquarium plants can you choose without CO2 injection? A selection of hardy, easy plants for a beginner's planted tank.
- Budget for a first brackish water aquarium: the real cost to get startedBedding & habitat
How much does a first brackish water aquarium cost? Tank, filtration, salt and salinity monitoring, budgeted item by item.
- Changing filter media too often: the mistake that wrecks your aquarium's cycleCare & grooming
Why you should never replace all your filter media at once: nitrifying bacteria, replacement frequency and the right habits.
- Restarting a neglected aquarium: a step-by-step guideCare & grooming
How do you restart an aquarium that's been left neglected without endangering the fish? Steps, water changes and mistakes to avoid.
- GH, KH and pH: understanding and adjusting aquarium water hardnessCare & grooming
GH, KH, pH: what do these three readings actually measure, and how do you adjust aquarium water hardness without stressing the fish?
- Upgrading to a bigger aquarium: moving your fish without the stressBedding & habitat
How do you upgrade to a bigger aquarium without breaking the biological cycle or stressing your fish? Steps and mistakes to avoid.
- Aquarium electrical safety: GFCI protection and good habitsTravel & safety
Heater, filter, lighting near the water: what electrical precautions keep an aquarium safe for fish and people?