Goldfish Care Guide: Tank, Food and Lifespan

Quick answer

Goldfish are hardy, but they are not "bowl fish". They grow big, make a lot of waste and live 10 years or more when they're kept properly. Fancy goldfish need a large filtered tank. Common and comet goldfish need a very large tank or, better, a pond. Change the water regularly and feed small amounts of a good goldfish food.

Two kinds of goldfish

Where you can, keep the two types apart. The slim-bodied fish are quicker and tend to beat the fancies to the food.

Tank size

A goldfish needs far more water than its size in the shop suggests. Experienced keepers don't all agree on numbers, but a widely used rule of thumb for fancy goldfish is a tank of at least around 75–110 litres (20–30 US gallons) for the first fish, then roughly 40 litres (10 gallons) more for each extra fish. Common and comet goldfish need more again, and a pond is usually the best long-term home for them.

More water dilutes waste and keeps conditions stable, and stable water is what keeps goldfish healthy. Choose a long tank with a big surface area over a tall, narrow one: oxygen gets into the water at the surface.

Filtration and water quality

Goldfish are messy. Buy a filter rated for a bigger tank than yours and leave it running all the time.

• Cycle the tank before adding fish. A new tank doesn't yet have the bacteria that break down waste. Read The Aquarium Nitrogen Cycle, Explained Simply before you start.
• Partial water changes: commonly 20–30% weekly, using a dechlorinator and water close to the tank temperature.
• Gravel vacuuming: pull waste out of the substrate while you do the water change.
• Filter maintenance: rinse the media in old tank water, never tap water, and never replace all the media at once.
• Test regularly: ammonia and nitrite should be zero, and nitrate should stay low.

Temperature

Goldfish are cold-water fish. Most fancy goldfish are happy at roughly 18–24 °C (64–75 °F) and cope well with cooler water. Warm water holds less oxygen, so step up the aeration in hot weather. Sudden temperature changes stress fish; avoid them.

In many climates single-tail goldfish can see out a cold winter in an outdoor pond, provided the pond is deep enough not to freeze solid and part of the surface stays open for gas exchange.

Setting up the tank

For substrate, use smooth gravel too big to swallow, fine sand or a bare bottom. Goldfish sift through the substrate constantly and can choke on mouth-sized gravel. Decorations should be smooth with no sharp edges, because fancy goldfish injure easily, especially types with delicate eyes such as bubble-eyes.

Hardy plants stand the best chance against goldfish nibbling: anubias, java fern and floating plants are good choices. A lid stops jumping and cuts evaporation. An air pump, or strong movement at the surface, keeps oxygen levels up.

Feeding

Goldfish are omnivores and always act hungry. Overfeeding is one of the commonest causes of poor water and digestive trouble.

• Feed a quality goldfish pellet or gel food as the staple. Sinking pellets suit fancy goldfish, which can gulp air when they feed at the surface.
• Feed small amounts once or twice a day, only what they finish in about a minute or two.
• Add vegetables now and then: blanched peas (skins off), spinach or courgette (zucchini).
• Give the odd treat such as bloodworms or brine shrimp.
• Take out any food left uneaten.

Fancy goldfish are prone to buoyancy problems (swim bladder issues), which can be tied to diet, overfeeding or water quality. Sinking foods plus some vegetables is the usual advice.

Tank mates

Goldfish do best with other goldfish of a similar type. Most tropical fish need warmer water, and small fish may get eaten. Goldfish are social, so two or more is generally better than one, as long as the tank is big enough.

Lifespan

Given a large tank and good water, goldfish commonly live 10 years or more, and some go on much longer, particularly in ponds. Stunting and early death usually come from small tanks and poor water. They are not a "natural" goldfish lifespan.

Common mistakes

• Bowls or tiny tanks with no filter.
• Adding fish to an uncycled tank.
• Overfeeding.
• Keeping slim-bodied and fancy goldfish together in a small tank.
• Changing all the water or scrubbing the filter in tap water.
• Releasing unwanted goldfish into rivers or lakes, which can harm wild ecosystems and is restricted in many places.

Health warning signs

Watch for clamped fins, sitting on the bottom, gasping at the surface, white spots, red streaks, frayed fins, cotton-like growths or loss of balance. Test the water first every time, because poor water quality is behind a lot of these problems. White spots may be ich; see our Ich (White Spot) treatment guide. If the fish don't improve, get advice from an aquatic vet or an experienced keeper.

In Pakistan

Goldfish are easy to find in Pakistani aquarium markets. Summer heat is the real problem. In cities where rooms reach the mid-30s °C (mid-90s °F) or higher, keep the tank away from windows and outside walls, add aeration with an air pump, and use a lid that still lets air through. Don't put ice straight into the tank, as it causes sudden temperature swings. Load-shedding cuts power to filters and air pumps, so a battery-powered or UPS-backed air pump is worth considering.

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