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Thread: Flow from a 4" Bottom Drain

  1. #11
    MCA is offline
    Honmei MCA's Avatar
    Join Date
    Dec 2003
    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.
    Koi keeping is not a belief system; it is applied science with a touch of artistry.

  2. #12
    Nisai KDSD's Avatar
    Join Date
    Jan 2007
    For example, what I have soaked up is - The Large Nexus filter is designed for a 4" feed and in doing so, puts a MAXIUM SPEED LIMIT on that filter of 3600 GPH. I have not read the manual personally but have talked with several different sources regarding the performance of the filter. So in regards to the large NEXUS filter; What is the OPTIMAL flow rate recommended on a 4" gravity flow BD? Aerated or not?
    Per the flow rates of the Nexus, I will be putting a flow meter on the 4" line to see just that in the next few weeks..........what is the actual flow rate based on a recommened 2" drop of in main bio area water line from dead start. But of course I could just wait till next Sat at our Koi show to ask the man himself. I understand he will be with Bill D. per talking with Bill on phone this am.

    Nexus Eazy 300
    Max flow rate: 15,000 litres/hr 3,300 UK or 3,900 US gallons/h

    This is what the Mfg. has in pdf instruction book, so based on that fact we need to know what really is true flow rate. From field experiance I will take an educted guess of 3100-3400 gph.

    Faster and higher flows are not always the best option


  3. #13
    Tategoi The Pond Digger's Avatar
    Join Date
    Dec 2007
    Redlands, California

    Optimal Flow Rates...........

    Let us mention that faster and higher flows being, or not being, the best option could also depend on what you are flowing too.

    Strictly speaking of Bottom Drain Circuits, understand that if you are flowing into a settlement tank, a slower flow rate would be more optimal than faster flow rates, to increase the dwell time in the settlement chamber thus allowing solids to settle out.

    However, if you are running your BD into a sieve, like the CETUS, then dwell time is really not of concern. Of course, this is all based on ponds with normal stocking rates, feeding regimen, optimal temperature considering frost lines, etc., and so on. I am sure we will have fans of sieves on BD circuits and then we will have polar opposites.

    So many variables is the construction of traditional koi ponds.

    The Pond Digger Grow Out Stats


    The Pond Digger
    Last edited by The Pond Digger; 02-11-2008 at 02:56 PM. Reason: More to say..........YOU KNOW ME!
    "Doubt sees the obstacles, Faith sees the way!"

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