Autumn Koi And Goldfish Pond Maintenance

Autumn is the time to reduce the amount of leaves and decaying material entering a fish pond, check water quality and prepare equipment for colder weather. This guide is for ornamental ponds containing koi, goldfish and similar fish. Wildlife-only ponds generally need less intervention.

Autumn Pond Maintenance Checklist

• Remove heavy leaf fall before it sinks; use a net if trees overlook the pond.
• Cut back dead or decaying plant growth without stripping the pond bare.
• Remove excessive sludge where needed, rather than trying to make the pond spotless.
• Test ammonia, nitrite and pH and investigate any abnormal readings.
• Check pumps and filters; follow the manufacturer’s instructions for winter operation.
• Reduce feeding as the pond water cools and use suitable food for the season.
• Prepare a safe way to maintain gas exchange if a fish pond freezes.

Remove Leaves Before They Sink

A few leaves are unlikely to cause a problem, but remove large amounts before they become waterlogged and sink. If trees overhang the pond, a pond cover net can reduce leaf fall. Clear leaves from the net regularly so their weight does not pull it into the water.

You can also remove surface debris with a pond net or a floating pond skimmer. Check removed plant material for wildlife and leave it beside the pond for around 48 hours before composting it.

Cut Back Dead Pond Plants Carefully

Remove dead or decaying leaves and stems where practical, but do not strip the pond bare. Some healthy growth can remain, and marginal vegetation can provide shelter for wildlife. The RHS recommends leaving cut material beside the pond for 48 hours to give creatures time to return to the water.

Some plants need species-specific care. For example, check the RHS guidance before cutting back plants such as Gunnera, which may need their foliage left in place for winter protection.

Should You Remove Pond Sludge in Autumn?

Remove excessive accumulations of sludge and settled organic waste, but leave some natural sediment in place. A complete pond clean-out is not usually necessary and can disturb fish, plants and pond life.

If a significant layer has built up in an ornamental fish pond, a pond vacuum can remove settled waste without draining the pond. Concentrate on areas where leaves and other debris collect, and follow the vacuum manufacturer’s instructions.

Test Water and Check the Filter

Test ammonia and nitrite; both should be zero in a healthy established fish pond. Monitor pH as well. If ammonia or nitrite is detectable, investigate rather than assuming colder weather will solve the problem. A suitable pond water test kit makes routine checks easier.

Check that water flows freely through the pump and filter. If biological media needs rinsing, use water removed from the pond rather than untreated tap water. OATA warns that chlorine or chloramine can damage beneficial filter bacteria.

Whether a pump, filter, UV clarifier, fountain or waterfall should run through winter depends on the equipment and installation. Follow the manufacturer’s instructions rather than switching everything off automatically. If parts need replacing, see our pond filter and pump spares.

How Should You Feed Koi and Goldfish in Autumn?

Reduce feeding as pond water cools and fish become less active. Offer only what they will readily eat, so uneaten food does not add to the pond’s waste load.

As temperatures fall, OATA recommends changing to a lower-protein, more easily digested food such as wheatgerm pond fish food. Use water temperature, not daytime air temperature, to guide feeding. Below approximately 8°C, OATA says it may be better not to feed koi and goldfish at all. Sturgeon are different and should continue to be fed throughout the year.

For feeding quantities and the full seasonal guidance, see how and when to feed your pond fish.

Prepare for Freezing Weather

If a fish pond freezes over, do not smash or crack the ice; the shock waves can harm fish. Prepare an appropriate way to maintain an opening, such as a suitable pond heater or floating device. If the pond is already frozen, the RHS advises gently melting an opening with a pan of hot water held on the ice. Do not pour boiling water directly into the pond.

For advice on equipment, fish and pond care once winter arrives, see our guide to looking after a pond in winter. If you are planning the next seasonal restart, see getting your pond ready for spring.

Need More Help Preparing Your Pond for Winter?

If you are unsure how much sludge to remove, how to adjust feeding or whether your equipment should run during winter, our experienced team is happy to help.

You can ask our pond experts a question online or call us on 01778 341199 for friendly, practical advice.

Sources and Further Reading

• Royal Horticultural Society (RHS) – Pond care
• Royal Horticultural Society (RHS) – October pond care
• Ornamental Aquatic Trade Association (OATA) – How to look after pond fish

Last reviewed: September 2026

Water Gardening Direct has supplied pond equipment and provided practical pond care advice to UK pond keepers for over 25 years.