November by the pool: the month's checklist before the first frosts

November is when the pond enters a new phase. In Belgium, the last leaves often fall heavily, the water drops below ten degrees, and the first frosts often arrive without warning. The fish move to the bottom and the plants die back. What is not done in November is done badly in December: frozen hands, icy water, and fish we no longer want to disturb. Here is the list of tasks, in the order in which we carry them out ourselves on the garden centre's ponds.

Why November is a pivotal month

In October, there is still time to catch up on many things: the water is cool but not cold, the fish still eat a little, and the filter bacteria are still active. In November, most of these processes switch to standby mode. All the organic matter that falls into the water at that time will sink, accumulate on the bottom, and slowly decompose throughout the winter, consuming oxygen and releasing gases. Limnology textbooks, such as Wetzel's, describe this mechanism clearly in ice-covered bodies of water: the organic load accumulated before winter largely determines the condition of the water when the ice thaws.

In other words, every bucket of leaves removed in November means less sludge and fewer algae in April.

The week-by-week checklist

Leaves: the number-one task

If you stretched a net in October, November is the time to empty it regularly: a net weighed down with wet leaves eventually touches the water, and the leaves steep in it. For leaves that have already fallen to the bottom, a fine-mesh net is enough in a small pond; beyond that, a pond vacuum saves a lot of time. There's no need to aim for perfection: the goal is to remove most of it, not sterilize the bottom.

Take the opportunity to remove yellowing water lily leaves by cutting the stem as low as possible, along with dead parts of floating plants. For bank plants with hollow stems, such as rushes or reeds, leave some of the stems protruding above the water: they shelter insects and contribute slightly to gas exchange beneath the ice.

Food, bacteria, and UV

Feed less over the weeks, using a light wheat-germ food, then stop when the water remains cold for a prolonged period, around 6 to 8 °C according to breeders. Fish almost stop eating on their own: don't force them.

Filter bacteria slow down considerably as the water cools, as Boyd and Tucker point out. Some bacterial formulas are presented by their manufacturers as suitable for cool autumn water; they can help break down organic deposits as long as the water is not icy cold. Use them preferably at the beginning of the month.

The UV clarifier is no longer much use: suspended green algae hardly develop in cold, poorly lit water. Turn it off, clean the quartz sleeve, and store the bulb in a dry place. An outdoor UV unit left full of water can burst during the first severe frost, quartz and all.

Pump, waterfall, and pipes

The waterfall is shut off in a pond with fish: it cools the water and can form ice blockages that divert water over the liner. The pump is either raised so it no longer draws from the bottom, or removed, cleaned, and stored in a frost-free place. Surface-running pipes and above-ground filters are drained or insulated. Don't forget the outdoor tap used to top up the pond.

Anti-gel and heron

In late November, install something that will keep an opening in the ice: an anti-freeze float, a small heater or an aerator whose diffuser is placed at shallow depth. Complete ice cover for several days prevents decomposition gases from escaping.

As for the grey heron, it is often more present in winter, when prey is scarce elsewhere, and sluggish fish are easy targets. It is a species protected by the European Birds Directive: it can only be deterred, with a net, a taut line along the edge or a decoy, never harmed.

Also read

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Frequently asked questions

— Should you still feed the fish in November?

Very little, and only while the water is not persistently cold. When it remains around 6 to 8 °C, stop.

— Should the leaf net be removed in November?

You can leave it as long as it remains taut above the water, to protect against the heron. Remove it or reinforce it if snow could make it sag into the water.

— Can you still plant in the pond in November?

It is no longer the ideal period. It is better to note the areas that need replanting and plant in spring, when the water warms up.

— When should the anti-freeze device be installed?

Before the first prolonged frosts, therefore generally in late November in Belgium. It is better to have it in place a little too early than too late.

In summary

• Removing leaves in November means less sludge and algae in spring.
• Food reduced and then stopped when the water remains cold.
• UV turned off, cleaned and stored; waterfall turned off; pipes drained.
• Anti-freeze device or surface aerator in place before prolonged frosts.
• Net kept taut against the heron, a protected species to be deterred without harming it.

Last updated: September 29, 2026.