Why you need to know the volume of your pond's volume ........

A. In a lake or natural pond you will find relatively few fish. A natural water system can only cope with a certain fish density in view of limited food sources and biological capacity. Many lakes have lots of small fish which are stunted. The capacity is based upon total weight essentially - so you can have many small fish competing for scarce food or less large fish.

Where you find large fish they eat the small fish in egg or fingerling stages.

In a pond there are almost always too many fish and that is why a biofilter is absolutely essential. To be able to build or buy the right pond filter you must know the pond volume.

The volume of water together with the stocking density determine the physical size and more importantly the amount of biomedia required to create a good biofiltration system.

• Take the following information as a rough guide (you can always add more but not less biomedia) for how much biomedia you need to treat a pond volume of 250 gallons or 1,000 litres
• Plastic tubes 1 inch diameter and 1 inch high (hollow): 8-10 gallons
• Plastic balls 1 inch diameter: 12-15 gallons
• Lava rock: 2 gallons
• Open cell foam: 5 gallons
• Alfagrog sintered ceramic: 1/2 gallon
  
  Multiply the above by 4.5 to convert to litres
  
  Biomedia is of course the surface upon which the bacteria responsible for keeping the pond water pure reside. Obviously
  the greater the surface area then the more bacteria you can have
  and the better your biofilter will perform.
  
  I have created a new web page covering this in more detail at
  
  http://www.clean-garden-ponds.com/biologicalpondfilter.htm
  
  
  B. Pond volume is also required to specify the size of the uv or  ultra violet light you need to prevent algae making your pond go green.  For a pond of around 250 gallons in full sun and highly stocked
  a 4 watt UV will do the job. This will also be big enough for a pond with very few fish and situated in the shade of 700 gallons.
  
  This assumes the UV comes equipped with a quartz tube to ensure the UV runs at peak efficiency.

For a pond with average stocking an 8 watts UV will handle pond volumes up to around 1200 gallons depending upon the sun/shade situation.
The rule is as follows:

Lots of sun, lots of fish, high water temperature then more UV power will be required. If you find you have specified an UV that is too small it is possible to add an extra one of the same size. For example 2 by 4 watts units is the same as an 8 watts unit.

You can switch off the UV at night if you really want to but it is not recommended. This will allow your UV light source to last longer.

In winter, in cooler climates, it is ok to shut down the UV light.

C. If you ever need to add chemicals to your pond then knowing the pond volume is critical. The reason is because all treatments work on the principle of so many ozs per 100 gallons, gms per litre and so on. Taking a chance or guessing the volume may kill your fish.

D. A fourth reason you might need to know the pond volume is to be able to specify your pond pump. However this was covered in detail by the calculator offered in the previous edition. Remember you can
still get the calculator here: http://www.practical-water-gardens.com/freecalculators.htm