For the filter system as a whole we take the actual volume of your pond and then add to this volume various "conditioning factors" to take into account your particular circumstances.

For example:
We add 25% if your pond is in full sunshine - because if it is, the water will warm up quicker, and algae will grow faster.

We add 25% if your pond is less than 2' 6" deep (75cm) - because a high percentage of the water in the pond is exposed to the full power of the sun and algae will grow faster.

We add between 15-35% to your pond depending on where you live, if the pond is in Manchester in the UK, its going to be cooler and less sunny than if the pond is in Florida USA. If it is hotter and sunnier then algae and fish will grow faster.

This then gives us an effective pond volume, which is the amount of water we need to filter. For a filter to work though, the entire effective volume of the pond has to pass through it approximately once every two hours.

For example:
A pond 0.9m x 0.9m x 0.9m (3' x 3' x 3') in full sun in Cape Town (South Africa) would have an actual pond volume of approx. 730 litres (160 gallons).

In this example we would add 25% for the pond being in full sunshine and 35% for the lovely Cape Town climate giving a total addition of 60%. Therefore, we must filter the ponds effective volume of 1170 litres (275 gallons), and any pump used should have a flow rate of at least 585 litres per hour (130 gallons per hour).

So we would filter the pond as though it had 261 gallons of water in it, and any pump we use should have a flow rate of 130 gallons per hour.

If you would like us to recommend a guaranteed filter system please visit our interactive Pond Selector pages.