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Stocking levels
With the vast improvements in filter media now, the old adage that you must have a filter with a surface area one-third the size of the pond does not add up. Filters like the Nexus and Bead filters allow for a massive volume to be filtered by a unit with a very small footprint. Because of this, it is impossible to put an exact guide on how big a filter and filter area you will need for a given volume of water, so follow the specifications of the unit that you are purchasing.
With this, as long as you have a filter system on your pond that is maintaining good water quality, the stocking level is up to you. However, the higher the stocking level, the slower the rates of growth you can expect, as well as overall development. Plus, you may find that you have to increase the frequency and amount of water changes and filter maintenance that has to be carried out!
As a very basic guide, the following is still considered by many a good guide for working out the stocking level in your Koi pond:
50in of Koi per 1,000 gallons of pond water (in a well-filtered Koi pond)
A factor that is worth considering (which will ultimately affect stocking, especially with more traditional styles of filter) is the retention time of the water flowing through the unit. The ideal flow rate is the whole gallonage of the pond once every two hours, so work this out by halving your pond’s volume, for example, a 1,000-gallon pond divided by two gives a flow rate of 500 gallons per hour.
From this, you may want to work out the retention time of your filter to see if it is in the region of 10 to 15 mins – the time considered to be acceptable for a pond. To do this, you will need the volume of the filter (the amount of water it holds when in operation) and the pumping rate of your pump. Armed with this information, the following formula can be used:
Filter retention time = filter size/pump rate
For example, if you have a 1,000-gallon pond, you want to be pumping the water at 500 gallons per hour, ideally. If your pump rate is 500 gallons an hour and your filter capacity is 100 gallons then 100/500 = 0.2 hours retention time, which is approximately 12 minutes and within the acceptable time bracket.