How do I calculate the right pond filter and pump size for my pond?

When selecting the best filter and pump for your pond, you must consider:

1. The Volume of Your Pond:
You can easily calculate your pond’s water volume by using the pond dimensions. Simply multiply the pond’s length x width x depth x 1000. The result will equal how many litres of water your pond holds.
  • Example: You have a koi pond that measure 3 metres in length, 2 metres in width, and 1.5 metres deep.
    • 3m x 2m x 1.5m x 1000 = 9000
    • Your pond capacity is 9000 litres.

When choosing a filter for your pond, for maximum effectiveness it is recommended that the filter can process 150% of your pond water. An easy way to work this out is to simply multiply your pond’s capacity in litres by 1.5.
  • As per the example above – let’s say you have a 9000 litre pond:
    • 150% of 9000 -> 9000 x 1.5 = 13,500
    • You will want a pond filter that is suitable for ponds up to 13,5000 litres.

Now that you have worked out the best pond filter to fit your pond, you will need to make sure you have a pump with a flow rate that is suitable for your pond and the filter. For the cleanest, most healthy pond water, we recommend that the volume of water in the pond should be passed through the filter once every hour. A general rule is that the pump’s flow rate will have to match the volume of pond water.
  • In a 9000 litre koi pond the recommended pond pump will have to have a maximum flow rate of 9000 litres per hour.
  • Keep in mind, you can use a slightly larger pump, BUT the pump flow rate cannot exceed the filter’s maximum output.
    • In the example we are using, your filter has a maximum output of 13,500 litres per hour. You can use a pump with a maximum flow rate between 9000 – 13,500 litres per hour.

2. Water retention time:
As mentioned above, it is important that your pond pump’s flow rate does not exceed the pond filter’s maximum output capacity. This is because you need your pond water to spend enough time processing through the filter unit. If the pond pump’s flow rate is too much for the filter, the water will move too quickly through the filter and returned to the pond before it can be properly cleaned.

3. Pond Turnover
Besides water retention time, the pond filter will need to process water faster than the time it takes for pollutants to produce – this is called the pond turnover rate. Pollutants in your pond can be caused by livestock, fish food, loose leafs in the water, etc. that all produce ammonia.
For most koi ponds, water turn over can happen at least once every two hours, but once per hour is best. As mentioned earlier, if you had a 9000 litre pond, you need a pump that can manage 9000 litres per hour.
Based on the koi pond example being used throughout this article, the PFC-20000 and the AquaECO-10000 are the ideal systems to be using. Here’s why:
The PFC-2000 pond filter is suitable for ponds with heavy stocked koi up to 10000 litres; ponds with small mix of fish and koi up to 12,000 litres; and suitable for decorative ponds up to 20000 litres volume. The AquaECO-1000 has a maximum flow rate of 10,000 litres per hour which will not exceed the filter’s output.
Remember, these numbers depend on the type of pond you have. Ponds can range from decorative to heavily stocked koi ponds. Heavily stocked planted koi ponds will produce more pollutants and will require the measurements used in the example above. If you have a smaller decorative pond, these numbers will be reduced.


For more information and advise please contact our sales team on 01895 813 000.