2 reasons Why you need to know the volume of your pond

1. 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 stunted fish and only a few larger fish (which eat the small ones). The fish holding capacity of course is based upon total weight essentially - so you can have many small fish competing for scarce food or less large fish competing for the food available (these lucky fish mainly eat those stunted fish trying hard to say alive on scare food resources.. This situation is typical of Irish and Scottish mountain lochs.

You wont find large populations of both types (small and large) in natural systems normally although of course you can expect to see a fair split of sizes.

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).

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 bio filter will perform.

2. Pond volume is also required to specify the size of the 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 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. 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: Free pond calculator go to this page to download the pond calculator