What size pond pump do I need?

Buy the flow you still have at the top of the waterfall, not the biggest number on the box. That box figure is the flow with no lift.

The turnover PondXpert publishes

PondXpert's pump and filter guide works from volume in litres: length × width × depth × 1,000. Their example is 3 × 2 × 1 × 1,000 = 6,000 litres.

• Goldfish. Turn the pond over once every two hours. Choose a pump at half the volume per hour. A 6,000 litre pond wants about 3,000 litres per hour.
• Koi. Turn the pond over once an hour, because koi produce more waste. The same 6,000 litre pond wants about 6,000 litres per hour.
• Wildlife, no fish. The RHS says a pond with few or no fish should not need a filter. Do not buy a fish-sized pump "just in case" and then point it at tadpoles. If you want a small fountain, size that feature from the maker's curve and use a pump with a guard that will not shred pond life. The RHS wildlife page asks for that protection.

Use average depth if the pond has shelves. Using the deepest point for the whole area overstates the litres.

Head height is where people undersize

Every metre of lift, and every tight hose, cuts the flow. Hozelock's Vorton instruction booklet tells you to size the pump for the vertical distance from the water surface to the filter inlet, plus an allowance of 0.6–0.9 m for hose friction. A waterfall whose lip is 1 m above the pond is therefore in the region of 1.6–1.9 m on the pump curve.

The planner shows that range. It does not invent a universal "lose 20% per metre" rule, because pumps do not all fall off at the same rate. Read the curve for the pump in your hand.

Two Oase pumps, from Oase's figures

We haven't tested this. Figures are as the maker states them (checked 13 November 2026).

Oase AquaMax Eco Classic 8500. Oase's UK page lists 80 W, a maximum flow of 8,300 litres per hour, a maximum head of 3.2 m, debris up to 8 mm, a 10 m cable, and hose tails for 25, 32 and 38 mm. It can be set up underwater or dry. The model name says 8500. The published maximum flow is 8,300 L/h, not 8,500. On 13 November 2026 the Amazon UK listing (ASIN B00B4ENASK) showed £265.04. That listing's specification grid also says "8.3 litres per minute", which is about 500 litres per hour and does not match Oase. Use Oase's 8,300 L/h. The same Amazon description prints 5,700 L/h at 1 m and 3,000 L/h at 2 m. Those mid-curve numbers are the listing's claim. They are not on the Oase specification table we checked, so confirm them on the current data sheet before you rely on them.

View the AquaMax Eco Classic 8500 on Amazon UK

Oase AquaMax Eco Classic 2500 E. Oase's data table for this model lists 23 W, 2,600 litres per hour and a maximum head of 2.2 m, with IP68 protection. The Amazon listing (ASIN B07NGNBJR8) agrees with those three figures and also states debris up to 8 mm, a 10 m cable and 25/32/38 mm hose tails. On 13 November 2026 the listing price was £139.64.

View the AquaMax Eco Classic 2500 E on Amazon UK

How those two sit against a 6,000 litre goldfish pond

You want about 3,000 L/h at the real head. The 2500 E's zero-head flow is already 2,600 L/h, and its maximum head is only 2.2 m, so once you add lift and hose friction it is likely to be short of 3,000 L/h. The 8500 has headroom at zero head (8,300 L/h, 3.2 m maximum). Whether it still delivers 3,000 L/h at 1.6–1.9 m is exactly the curve question. A koi pond of 6,000 litres wants about 6,000 L/h at that same head, which is a harder job and usually a larger pump.

Running a pump all year is not free. At the Ofgem Direct Debit average of 26.32p per kWh for 1 October to 31 December 2026, an 80 W pump left on continuously is 700.8 kWh, about £184 a year, before the standing charge and before your own tariff. A 23 W pump on the same basis is about £53 a year. Enter the watts of the pump you are actually considering in the planner. The price cap is an average for England, Scotland and Wales, not your bill.

What a pump does not do

PondXpert is explicit: a filter pump moves water. It does not filter it. Solids-handling means it can pass debris on the way to a filter, up to the millimetre size the maker states. It is not a substitute for the filter or the UV clarifier.

Any new outdoor circuit is a job for a qualified electrician, on an RCD. See pond electrics.

Should the pump run all winter?

The RHS October notes say to remove pumps and fountains, clean them and store them. The winter-care page also says a frozen fish pond needs some open water. Those are not the same instruction. Read winter care before you leave a pump in.

Why is my waterfall weaker than the box promised?

Almost always head, a narrow hose, or a blocked strainer. Read the flow at your height. Clean the strainer before you replace the pump.