[MCA]

as I posted on Koishack...


You can dimension BDs two ways: by gallons served or by area of floor space served.


Gallons served.
The shape of the curves in half of the oval make a huge different in the gallons the pond contains. When I calculate 9x7 (half of the oval) x 67% (the volume inside a sine wave) x 5 x 7.48 (gallons per cubiic foot, I get 1578.654 gallos. So the total volume would be a little over 3200 gallons. But that all depends on the shape of the oval's curve. The closer it is to a rectagle....the larger the volume inside the curve. You know the shape so indeed lets assume each half has 2000 gallons and the total is 4000 gallons.

Typically a koi pond system is designed to turn over the water through the filters in ~1 hour. The larger the pond...the more this target sildes towards 2 or even 3 hours do to the increasing costs of more BDs, filters, and pumps. So from a gallons servered perspective, using a 4" BD gravity feeding one fitler system....this pond could be served by one BD/filter/pump combo doing 3000-3500gph. And tha does not take into consider any water going through a skimmer to a pump (through some type of filter?) and back to the pond. Such a system should be just fine.


Floor space served
A BD can help gather sinking debris/mulm from the pond floor. The antivortex cover over the BD keeps the "suction" aimed parallel to the pond floor. That suction is strongest at the BD and disapates as you get further from the BD. So folks willl plan a BD doing ~3000gph to service floor area in a max radius of 6-8'. So if we put one BD in the middle of a 9x14 oval, the width of 9' is probaly served well enough. The problem may be in the 14' length. You may tend to get settlement in the ends of the oval.e. One way to address that would be to put TPRs at each end of the 14' length to help prevent any settlement. Another choice would be to put a BD in each logical half of the oval. If the BDs were 4" the flow for each should be ~3000gph to prevent settlement in the pipe. If the BDs and pipe were 3" the flow on could be ~2000gph. Don't forget to use BDs with air domes in either case!!!


Bottom line....from a gallons served perspective, one 4" BD feeding filters should be just fine...especially if the skimmer circuit also has filtration. From a floor space perspective you could get by with one 4" BD and pipe if you carefully place TPRs to prevent settlement in the ends of the oval. Another choice would be a 3" BD in each half of the oval.