RSPCA Australia sets 50 litres as the minimum for goldfish, with the tank at least 4 times the fish’s adult length, 2 times wide and 3 times tall. Run an efficient filter, hold 20 to 24°C, and cycle the tank first. Feed once a day, only what the fish finish in under 2 minutes.
Here’s how to set up a fish tank for goldfish. Start with at least 50 litres, add a strong but adjustable filter, fill with treated water, then cycle the tank before any fish go in. Goldfish make a lot of waste and get big, so size the tank to the adult fish, not the shop-bought baby. Bowls are out.
Legality and scope: goldfish are legal pets, but they are a pest fish once they reach a creek or river, and releasing them is restricted or illegal in parts of Australia. South Australia lists goldfish as an exotic species that may not be released into any waters without authorisation. The rules differ by state and change over time, so check your state Fisheries or Biosecurity department before buying. This guide covers common and fancy goldfish in a tank, not a pond.
New to fishkeeping altogether? The generic how to set up a fish tank guide covers the basics, and the Tank Setup guides go deeper. This post covers what changes for goldfish.
How Big a Tank Do Goldfish Need?
This is the step most beginners get wrong. Shops sell goldfish at 3 to 5 cm, but NSW DPIRD says goldfish are commonly up to 200 mm and can reach 400 mm in the wild. Pet goldfish rarely hit the top of that range, but a healthy one keeps growing for years.
RSPCA Australia’s goldfish page gives a formula: length at least 4 times adult body length, width 2 times, height 3 times, with 50 litres as the floor. Here it is worked through.
| Adult goldfish length | Minimum tank (L x W x H) | Volume |
|---|---|---|
| 10 cm | 40 x 20 x 30 cm | About 24 L, so the 50 L floor applies |
| 15 cm | 60 x 30 x 45 cm | About 81 L |
| 20 cm | 80 x 40 x 60 cm | About 192 L |
The volumes above are calculated from RSPCA’s formula and the outer tank dimensions, so real water volume is a bit less. RSPCA doesn’t give an extra-per-fish figure on this page, so treat each row as a single-fish floor and go bigger for every extra goldfish. Check your own tank with our litres guide.
A 60 cm tall tank is unusual, so for a big fish you will more likely buy a longer, wider tank and accept a lower height. Whatever you choose, goldfish tank roundups show what’s actually on sale.
How to Set Up a Fish Tank for Goldfish, Step by Step
- Choose a level spot. Water weighs 1 kg per litre, so a 190 litre tank needs a proper stand. Keep it away from windows and heaters. The stand roundup shows what’s on sale.
- Rinse the tank and decor in plain water. No soap or detergent. Pick smooth, rounded gravel or sand and avoid sharp ornaments, because goldfish sift through the substrate and can scrape themselves.
- Fit an efficient filter. Goldfish produce a lot of waste. RSPCA wants efficient filtration and an adjustable current that isn’t too strong, especially for fancy types.
- Add plants and cover. RSPCA recommends about 50 per cent cover. Real plants also soak up waste, though goldfish often eat or uproot soft ones, so choose tough species or artificial ones.
- Fill with treated water. Use a conditioner that says it handles chloramine, and dose for the full tank volume.
- Set up lighting. RSPCA says a maximum of 10 hours a day with at least 8 hours of darkness. A timer does this for you.
- Cycle the tank with no fish in it. This builds the bacteria that break down ammonia and takes about 4 to 6 weeks. Follow how to cycle a fish tank and test until ammonia and nitrite read 0.
- Add the goldfish. Float the sealed bag for about half an hour to even out temperature, then release the fish. Start with one or two, not the whole stocking plan, so the filter bacteria can catch up.
Some Australian water suppliers add chloramine (chlorine plus ammonia). SA Water says chloraminated water can contain free ammonia that many conditioners don’t fully remove, so read the label for the word chloramine and check your supplier’s water profile.
How to Set Up a Fish Tank for Goldfish: Temperature and Summer Heat
Goldfish are coldwater fish. RSPCA gives 20 to 24°C, which is cooler than a tropical tank. Most Australian homes won’t need a heater for goldfish most of the year, though a cold southern winter can drop a room below 20°C.
Summer is the bigger risk. A tank in a hot room can pass 24°C, and warm water holds less oxygen. Put a thermometer in the tank, keep the filter outlet breaking the surface, and keep the tank out of the sun.
Feeding and Routine
- Feed once a day, and only what the fish finish in under two minutes, as RSPCA advises. Overfeeding fouls the water and can make goldfish obese.
- Choose sinking food for fancy goldfish. RSPCA says sinking pellets help avoid gas bladder problems. The feeding guide covers amounts.
- Change 10 to 25 per cent of the water every week, with treated water, as RSPCA recommends, and test ammonia, nitrite and nitrate.
Common Mistakes
- Using a bowl. RSPCA says traditional fish bowls are too small for goldfish and should be avoided.
- Buying for today’s size. A 3 cm fish in a 50 litre tank is fine for a while. It won’t be in two years.
- Adding fish before the tank has cycled. Ammonia will hit the fish first.
- Mixing fancy types with fast, common goldfish. RSPCA says unusual varieties should be kept only with their own type.
- Releasing an outgrown fish into a creek. It’s a pest fish, and it can be illegal. Rehome it through a fish shop or your state Fisheries department.
When to Call It
If ammonia or nitrite still reads above 0 after 8 weeks of cycling, check the filter is running, don’t clean the media in tap water, and test your pH. If a fish sits at the bottom, clamps its fins or floats oddly, get a vet with fish experience to look at it.
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Frequently Asked Questions
What size tank does one goldfish need?
At least 50 litres, according to RSPCA Australia. The tank must also be 4 times the fish’s adult length, 2 times as wide and 3 times as tall. A fish that reaches 20 cm needs a much bigger tank than a 10 cm one.
Do goldfish need a heater?
Usually not. RSPCA gives 20 to 24°C, and most Australian rooms sit in or near that range. Use a thermometer, and add a heater only if your tank drops below 20°C in winter.
How long do goldfish live in a tank?
RSPCA says 10 to 15 years with proper care, with some varieties reaching 30. That is a long commitment for a fish often sold as a small prize.
Can goldfish live with other fish?
Some can. RSPCA lists white cloud mountain minnows and danios as suitable tank mates for common goldfish, and says unusual varieties should be kept with their own kind. A white cloud minnow may be restricted in some states, so check the local rules first.
Can I put a goldfish straight into a new tank?
No. A new tank has no filter bacteria, so ammonia builds up fast with a messy fish like a goldfish. Cycle it first.
