Should a Pond Pump Run All the Time, Including in Winter?

Why a filter pump should not be switched off

A biological filter works because colonies of bacteria live on its media and convert the ammonia that fish produce into less harmful compounds. Those bacteria need a continuous supply of oxygen, which arrives in the water the pump delivers.

When the flow stops, the water inside the filter becomes stagnant and oxygen runs down. If the pump is off for long enough the bacterial colonies decline, and when the pump restarts it can flush poor-quality water back into the pond. The filter then takes time to recover. How long a filter can go without flow depends on temperature and conditions, so we will not quote a figure, but the practical conclusion is the same: do not switch a filter pump off overnight to save electricity.

Fish also benefit directly. Oxygen levels in a pond are naturally lowest in the early hours of the morning, when plants and algae are consuming oxygen rather than producing it. A pump or waterfall that keeps the surface moving through the night helps.

What can go on a timer

If you want both economy and a big display, the tidy solution is two pumps: an efficient one sized for the filter that never stops, and a second for the waterfall or fountain on a timer. Our guide to running costs shows what each would cost.

Running a pump in winter

Winter advice differs between climates and between manufacturers, so treat the points below as the questions to answer for your own pond rather than a single rule.

In mild climates with little or no ice

Many pond keepers leave the pump and filter running all year. Fish are less active and eat little in cold water, so the filter has less to do, but keeping water moving maintains the bacteria and stops the surface freezing over completely during a short cold snap.

In climates with sustained freezing

• Waterfalls and streams can become a hazard. Ice can build up and form dams that divert water out of the stream and over the edge of the liner, draining the pond while the pump keeps running.
• Exposed pipework, filters and UV clarifiers can freeze and crack if water sits in them. Many manufacturers instruct owners to drain and store pressurised filters and UV units before hard frost.
• Deep circulation can chill the pond. In winter the water at the bottom of a pond is often slightly warmer than the surface, and fish rest there. A pump on the pond floor that stirs this layer up to the surface removes that refuge. If you keep a pump running, a common recommendation is to raise it to a shallower shelf.
• Keep a hole open in the ice. A fully frozen surface traps gases from decaying matter. A small air pump with the diffuser set in shallow water, or a purpose-made pond de-icer, is the usual way to maintain an opening.

Storing a pump for winter

If you take the pump out, clean it first using our cleaning guide, then store it somewhere frost-free. Manufacturers differ on how: some instruct that the pump be kept submerged in a bucket of water so that seals do not dry out, while others specify dry storage. Your manual is the authority. Drain and store filters, UV clarifiers and hoses according to their own instructions.

Restarting in spring

1. Inspect the cable, plug and housing for damage before anything goes back in the water.
2. Check that the impeller turns freely.
3. Reinstall the pump, filter and UV clarifier, and replace the UV lamp if it is due.
4. Start the pump and check every connection for leaks.
5. Remember that a biological filter that has been shut down needs time to re-establish. Feed fish sparingly at first and test the water.

Frequently asked questions

Can I turn my pond pump off at night?

Not if it feeds a filter on a pond with fish. A decorative fountain or a separate waterfall pump can be switched off overnight.

Will running the pump all the time wear it out?

Pond pumps intended for filtration are designed for continuous running. Frequent stopping and starting, running dry and clogged intakes are generally harder on a pump than steady operation.

Should I run my pond pump during rain or a storm?

Rain itself is not a reason to switch off. In severe weather, protect outdoor electrical connections, and if you have any doubt about their safety, disconnect at the house supply.