Pond pump: calculate the right size

Anyone who owns a garden pond with fish and aquatic plants should not do without a pump that cleans the water and at the same time adds oxygen. You should pay attention to the right size of the pond pump.

criteria for selection

If you are thinking about a pump for the garden pond, then the desired functions should be specified here in advance. A pump is not only necessary when there are fish and aquatic plants in the pond. So there are the following additional considerations:

  • a creek is to be fed
  • a water fountain or game is desired
  • the pump is connected to a water filter
Note: Even if you don’t have any fish in the garden pond, you generally cannot avoid purchasing a pond pump. Because this, in connection with a filter, is decisive for clear water and the quality of the water in general. This is especially important for a swimming pond.

Calculate pump performance

In order to find out the size and capacity of the pump required for the pond, in this example without a waterfall or stream, it is important to measure the pond if this was not done directly at the system. The pump capacity is the capacity of how much water has to go through per hour to keep the water clean and clear. The following factors must be taken into account:

  • Length (L) x width (W) x half depth (D)
  • gives pond volume (V) in cubic meters
  • Pond volume x number of filtrations (F) : 24 hours per day
  • results in pump capacity l/h

sample calculation

The example calculation was created using the above formula for calculating the pump output:

  • Pond volume 5 meters wide, 5 meters long and half of 2 meters deep
  • results in a calculation of 5 x 5 x (2/2) = 25 m³
  • Pond should be filtered four times a day
  • 100 m³ of water run through the pond pump in 24 hours
  • Basis of the calculation: 25 x 4 = 100
  • Pump capacity of 4.2 m³ per hour
  • based on the following calculation: 100 : 24 = 4.166
  • 1 m³ is the equivalent of 1000 liters
  • therefore rounded up 4.2 x 1000 = 4200
  • results in an output of 4200 l/h

According to this calculation, a pond pump with an output and a circulation cycle of 4200 l/h is required for a five meter long, five meter wide and two meter deep garden pond.

Tip: Many manufacturers indicate which circulation cycle their pumps are suitable for. You must therefore first calculate the required liters per hour based on the pond volume and then pay attention to the l/h specifications for the various pond pumps.

Note other criteria

However, the above calculation is only an approximate and simple calculation, because there are other criteria that have to be taken into account when it comes to the required pump capacity:

  • pond location
  • sun or shade
  • aquatic plants
  • fish stock

The more sun falls on a garden pond, the more pond plants there are and the more fish there are in the pond, whereby the size of the fish is also decisive here, the greater the performance of a pump must be. A simple garden pond with little pond planting or a pure swimming pond can therefore get by with the pump capacity calculated in the example. However, extras such as water features or a stream have not been considered here. A stream pump must be selected for this. A pure pond pump does not have the delivery head capacity for this.

Note: If you have the popular koi in your garden pond, for example, then a pond pump with a pump capacity of at least 15,600 l/h is recommended, as the fish need clean water and plenty of oxygen.

Kira Bellingham

I'm a homes writer and editor with more than 20 years' experience in publishing. I have worked across many titles, including Ideal Home and, of course, Homes & Gardens. My day job is as Chief Group Sub Editor across the homes and interiors titles in the group. This has given me broad experience in interiors advice on just about every subject. I'm obsessed with interiors and delighted to be part of the Homes & Gardens team.

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