Filters and filtration: rules and parameters

For every pond there is a specific size of filter that needs a specific size of pump to recycle the water through it. Some manufacturers with more sophisticated filter media and with ancillary accoutrements and 'add-ons' like Ultra-violet lamps and magnets, have reduced the theoretical size necessary to keep ponds of specific volumes clear, but they stick to some of the old rules for pond filtration.

1. The pond must be at least 18inches or half a metre deep.

2. The filter itself must be capable of processing half the volume of the pool every hour of the day and night.

3. Therefore there must be a pump that is capable of delivering this.

Example - 500 gallon pond needs a filter that is related to that gallonage together with a pump that can deliver 250 gallons to the height at which the filter is sitting. Situate the pump on the opposite side of the pond to the filter inlet for efficiency.

Over-specification is better than under-specification within reason. If the filter is churning over more than the TOTAL volume of the pool every hour the resulting commotion underwater can only be to the detriment of the fish and all the inhabitants of the pool.

By the way,

Total volume of your pond in gallons = length in feet x breadth in feet x depth in feet x 6.25

4. It used to be necessary to have a filter surface area that was one third that of the pool surface area. Modern manufacturers with compact multistage units claim otherwise. But it is useful to bear this in mind since a manufacturer's claim to guaranteeing water clarity does not guarantee the QUALITY of that water. After all, water containing ammonia and nitrites can be still quite clear !

5. The water must be well oxygenated - by waterfall, fountain, plants or air pump.