How to Look After a Goldfish Pond (and What to Feed Your Goldfish)

By Ann, gardener and garden designer at Ann's Garden Heaven

A pond brings a garden to life. The flash of orange goldfish, the sound of water and the dragonflies it attracts make it one of my favourite features. And the good news is that a well-balanced pond mostly looks after itself – you just need to get a few basics right.

Here's how I keep a goldfish pond clear and healthy all year, and exactly how to feed your fish.

Part 1: The right pond for goldfish

• Depth: make at least one area of the pond about 60cm (2ft) deep. Fish rest in the deeper, more stable water in winter, below any ice.
• Size: the bigger the pond, the more stable the water. Don't overcrowd it – as a rough guide, allow at least 50 litres of water for each goldfish, and remember they grow. Fewer fish means clearer water.
• Position: a spot with some sun but not baking all day, and away from overhanging trees that drop leaves.
• Shelves and a gentle slope: shallow shelves for marginal plants, and a sloping edge or ramp so frogs, birds and hedgehogs can get in and out safely.
• Safety: even shallow water is a drowning risk for small children. Fit a strong mesh grid over the pond, or fence it, if young children visit your garden.

Part 2: Plants – your pond's natural filter

Plants are the secret to clear water. They compete with algae for nutrients and light, give fish shade and shelter, and add oxygen.

• Water lilies and floating plants – aim to cover about half to two-thirds of the surface. The shade keeps the water cool and stops green algae taking over.
• Oxygenating plants – such as hornwort and water starwort, which grow under the water and help keep it fresh.
• Marginal plants – such as marsh marigold, water forget-me-not and flag iris, planted in baskets on the shallow shelves.

Avoid invasive plants. Water fern, parrot's feather, floating pennywort, Australian swamp stonecrop and water primrose have been banned from sale in England since 2014 because they choke rivers and ponds. And never put pond plants – or fish – into the wild.

Part 3: Keeping the water healthy

• Pump and filter: a goldfish pond needs a filter to break down fish waste. A UV clarifier built into many filters clears green water.
• Clean the filter the right way: rinse sponges in a bucket of pond water, never under the tap. Chlorine in tap water kills the helpful bacteria that keep the water safe for fish.
• Top up with rainwater from a water butt when levels drop. If you must use tap water, add a pond dechlorinator.
• Test the water every few weeks in the growing season with a simple test kit for ammonia, nitrite, nitrate and pH, especially if fish seem unwell.
• Remove debris: scoop out fallen leaves, dead plant material and blanket weed regularly. Leave blanket weed on the edge for a day so creatures can crawl back into the water.
• Don't clean too much: never empty and scrub the whole pond. A little sludge on the bottom is part of a healthy pond. If you must clear it out, do it in early autumn and only partly.

Part 4: What to feed your goldfish

The everyday food

• Floating pond sticks or pellets made for goldfish are the best everyday food. Floating food lets you see how much is eaten, so you don't overfeed.
• Wheatgerm food is easier to digest and is the right choice when the water is cool in spring and autumn.

Healthy treats (once or twice a week)

• Shelled peas, cooked or defrosted, squashed into small pieces
• Blanched lettuce or spinach
• Daphnia, bloodworm or brine shrimp (frozen or freeze-dried)
• Natural food in the pond – insects, larvae and soft plants

Never feed

• Bread – it swells, has little goodness and quickly pollutes the water.
• Fatty, salty or processed human food.
• More than they can eat – uneaten food rots and causes cloudy, unhealthy water.

How much and how often

Feed only as much as your fish will eat in about 3–5 minutes, then scoop out anything left. Overfeeding is the most common mistake pond owners make – and goldfish will always look hungry!

Feed by water temperature

Goldfish are cold-blooded, so how much they can digest depends on the water temperature. A floating pond thermometer is a cheap, useful tool.

• Above 10°C (late spring to early autumn): normal pond food, once or twice a day.
• 5–10°C (early spring and late autumn): switch to wheatgerm food and feed a little every few days.
• Below 5°C (winter): stop feeding. Their digestion slows right down, and food can sit in their gut and make them ill. They'll live on their reserves until spring.
• In a heatwave, feed lightly – warm water holds less oxygen, and digestion uses it up.

Part 5: Your pond through the year

Spring

• Start feeding wheatgerm food once the water is above 5°C, and switch to normal food above 10°C.
• Clean the pump and filter and restart them if they were off for winter.
• Divide and repot overgrown water plants, and add new ones.
• Expect a short burst of green water as the weather warms – it usually clears as plants grow.

Summer

• Top up evaporation with rainwater.
• Run a fountain or waterfall in hot, humid weather and during thunderstorms, including at night, to add oxygen. Fish gasping at the surface are short of oxygen.
• Remove blanket weed and trim back plants that cover more than two-thirds of the surface.

Autumn

• Stretch a net over the pond before the leaves fall – rotting leaves pollute the water.
• Cut back dying marginal plants and remove dead lily leaves.
• Switch to wheatgerm food as the water cools, and gradually feed less.

Winter

• Stop feeding when the water drops below 5°C.
• Keep a small hole in the ice so harmful gases can escape. Float a ball on the surface, use a pond de-icer, or stand a pan of hot water on the ice to melt a hole.
• Never smash the ice – the shock waves can harm or even kill your fish.
• Turn off fountains in freezing weather so the warmer water at the bottom isn't mixed with icy water from the top.

Adding new goldfish

1. Let a new pond settle for at least two weeks before adding fish, so plants and helpful bacteria can establish.
2. Buy healthy fish from a reputable aquatic centre – look for bright eyes, raised fins and active swimming.
3. Float the sealed bag on the pond for 20–30 minutes so the water temperature evens out.
4. Gently let the fish swim out, and don't feed them for the first day.
5. Add only a few fish at a time so the filter can keep up.

Common problems

• Green water: too much sun and too many nutrients. Add more plants for shade, feed less and fit a UV clarifier.
• Fish gasping at the surface: not enough oxygen. Turn on a fountain or air pump straight away and do a partial water change with dechlorinated water.
• Herons: a net, an edge of taut wire or a decoy can help. Plenty of deep water and plant cover gives fish places to hide.
• Sick fish: clamped fins, white spots or sitting on the bottom in warm weather are signs of trouble. Test the water first, then ask an aquatic specialist for the right treatment.

With good plants, the right food in the right amount and a little seasonal care, your goldfish can live for many years – often well over ten. Enjoy the peaceful moments watching them, too.

– Ann

Photos from Wikimedia Commons, shared under Creative Commons and similar free licences. Follow each link for the photographer and licence.