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Thread: What is good current?

  1. #1
    Tategoi Peppy's Avatar
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    What is good current?

    How much current is considered good? How do you measure it? I have a 1.5" eductor on one of the returns. It's supposed to multiply the output by 5.

    I also have a 1.5" venturi for the other return. I put it on, then take it off, then put it back on. Can't decide if it's good or bad!

  2. #2
    Nisai
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    measure the flow

    get a rubber duck (just for fun) and a stopwatch if the current expresses itself on the surface. time it past two marks on the pond wall and convert the rate to feet per second. there are rule of thumb standards using feet per second you can use. if the flow is below the water level you can test it with blue dye fed into the inlet. again measure the rate. you only need a ballpark measure that can be accurate to a broad window of speed. mine is at about 2 feet per second at 2 feet from the outlet.

  3. #3
    Honmei
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    Quote Originally Posted by Peppy View Post
    How much current is considered good? How do you measure it? I have a 1.5" eductor on one of the returns. It's supposed to multiply the output by 5.

    I also have a 1.5" venturi for the other return. I put it on, then take it off, then put it back on. Can't decide if it's good or bad!
    "Good" is a "relative" term. When looking at the curerent velocity, one needs to look at a number of variables in the purpose(s) of the currents. Are we looking at currents to move solids to pick up ooints to take them to filtration? Or, how about currents for exercise? A diffuser dome current creates a large current over the dome but yet a much smaller current at the perimeter.

    I personally prefer a current around 9 to 11 in/sec at the perimeter. this seems to do a good job at keeping the solids moving to filtration and reduces/eliminates target solids from settling. To measure such simplu use some floating beads and repeatedly measure the distance traveled and the time it takes. That should get you in the ball park.

    As for the eductors, let me do some calcs. You may be a tad surprised about them.
    The views presented are my personal views and not that of any organization that I may belong to unless otherwise specified. [email protected]
    CKHPA

  4. #4
    Honmei
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    Eductors, what do they do and not do?

    The laws of physics are kind of set in stone. Statements like, for every action there is an equal but oppsite reaction typically comes to mind.

    Eductors were design as a "mixing device" to combine liquids and mix thoroughly...and they do a good job at thier designed purpose. They work by decreasing the orrafice and speeding up the water (much like a venturi) which in trun pushes the liquid in front and draws liquid from behind (instead of air like a venturi) and thus combining the liquids in a mixture.

    But one must also understand some other rudimentary physics. Force = Mass X Acceleration.

    This formula can be looked at on both side of the eductor. Without an eductor, a given mass" volume of water" travels through a given pipe size at a given velocity. The force supplied is unchangeable (unless the force supplied by the pump itself changes). The velocity of the water can be changed by reducing the pipe or orafice size but in trun, the mass (volume of water) is decreased and the "Force" still remians constant (actually less due to some other forces that come into play such as increased friction loss in the piping). So, while the eductor increases the velocity of the water entering the pond, the "Mass" of the water decreases and the resulting force remains the same. It is this force that acts upon the greater body of water (again F= MA) that creates the current in the resulting current throughout the pond. So, in simplistic terms the actual pond current is the same with or without the eductor (abeit there is a stronger current at the mouth of the eductor nozzle).

    OK, but what other affects are there? I mentiomed added fristion loss (less resulting flow) nad less flow due to the orafice size. Dies this in turn have any adverse affects? Yepper, it sure does since now the "Mass" or volume of water flowing becomes less. This in turn adversly affects the pond's turn over rate if this circuit is combined with filtration (which it most likely would be since it make no sense to me at least to pump water and not also filter it).

    I know some a big fans of Eductors, and that is fine. My point is that the resulting outcome and trade offs might not be what you think they are. I had this conversation with Burt B some 8 or so years ago. Burt is a big fan of Eductors. Bottom line then was that I gave him the two I had laying around and he was glad to receive them

    The other negative about Eductors that bother me is yet another protrusion within the pond. I am a believer of eliminating things that pose additional risks to the koi. Koi like to paly in the current of the eductors and evenget up into the nozzles. Flight response could very easily cause koi to become injured on these devise...or at least, as stated earlier pose an additional risk.
    The views presented are my personal views and not that of any organization that I may belong to unless otherwise specified. [email protected]
    CKHPA

  5. #5
    Tosai
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    does anybody have a opinion on how much is good for exercise? is their an optimal level for koi to grow?

  6. #6
    Tategoi Peppy's Avatar
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    LOL! Leave it to you, schildkoi, to burst my bubble every time!

    That's okay. I come here for the expert knowledge, painful as it is sometimes. I want the real low-down, not candy-coated answers, and I'm happy I can count on you all for just that.

    Guess I'll measure the speed with and without the eductor and see what happens. It seemed like it really made a difference.

    As far as what kind of current I want, I have enough current to direct stuff to the retro BD. There are the two underwater returns from two 5500 gph pumps (before going through all the pipes and stuff) and two 150 lpm air pumps that are not on but real close to the retro BD.

    Everybody's always talking about koi needing current. So how much current do they need is what I wanted to know. I guess for exercise is what I'm asking.

    I don't plan on adding another pump (at least not right now) but I'm curious.
    ...enjoy your day!
    5500 gllns, Ultima II 4000, Tarpon 6000, 1 Multi-Cyclone Prefilter, 2 - 5500 gph pumps, 1 Retro BD, 1 skimmer, max depth 4', 5% trickle 24/7 weather permitting

  7. #7
    Daihonmei MikeM's Avatar
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    Quote Originally Posted by Peppy View Post

    Everybody's always talking about koi needing current. So how much current do they need is what I wanted to know. I guess for exercise is what I'm asking.
    There is no current in a mudpond. There is a lot of room for swimming and a soft bottom for digging. The Momotaro greenhouse pond in which so many fine koi are finished has relatively little current.

    I tend to doubt current is all that important for exercise purposes, but folks do talk about it. I do believe current is important for water quality. The continual mixing of water within the pond and exposure to the surface is a good thing. Even the best water has a smell (fragrance? ). It comes from the release of volatiles into the atmosphere. The more current, the more water molecules that get in touch with the surface, and the sooner the volatiles escape. At the same time, oxygenation is maintained at saturation levels. These are good things.

    The question should be: How much current is too much? If the koi cannot find an area in which to rest, there is too much current. In other words, you'll know when you see it. This can occur in a holding tank. I have not seen it in a pond.

  8. #8
    Tategoi andy's Avatar
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    Trying to describe the mechanics/dynamics of fluids through Eductors may not be as straight forwards as previously suggested. I agree they may provide less volume (mass) but do provide a much greater velocity (acceleration) resulting in greater (faster) pond current.

    I like eductors very much due to their flexibility. For instance they can be redirected based on the specific requirements..... But I've been concerned about having yet another "obstacle" for the Koi to get hurt.......

    I have seven eductors in my pond to circulate the water towards one end where the skimmer is located. Just recently I eliminated one of the eductors near the skimmer. This has created an area of calmness for the Koi. I've notice during night time they all gather in this area to sleep..... So IMO too much current is not the end all be all situation.

  9. #9
    Tategoi Peppy's Avatar
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    Not that I want the koi to get hurt, but I'm not super concerned about it. I guess more often than not they'd head for the bottom when spooked but they could blindly zip off in any direction. The current close to the eductor would hopefully slow them down some (some, now, some, not stop it) if headed that way. A possibility exists for a koi to zip toward the eductor at an angle that would enhance the koi's speed toward it. Understandably not a chance someone with show koi would dare to take but an odd angle for a spooked koi to approach my eductor the way it's situated.

    So for me, there's 1. the odds of a spooked koi that 2. is blindly spooked that 3. is headed toward the one odd angle where current will pull it forward toward the eductor or at least not slow it down some.

    MikeM, I was also thinking more current=more mixing.

    Andy, I couldn't get my head around the idea that with or without the eductor, the current is the same. I guess maybe that depends on the definition of current.


    From Merriam Webster (Current - Definition and More from the Free Merriam-Webster Dictionary)
    Main Entry: 2current
    Function: noun
    Date: 14th century
    1 a : the part of a fluid body (as air or water) moving continuously in a certain direction b : the swiftest part of a stream c : a tidal or nontidal movement of lake or ocean water d : flow marked by force or strength
    So if we're talking swift, force or strength, then I would think velocity is the main objective in increasing current as opposed to volume.

    And now, after hearing about current, current, current, the point is made about mud ponds.

    MikeM, I always think all is well with the pond when it smells like a fresh mountain stream. That is a smell but a clean smell. Is that the smell you're referring to?

  10. #10
    Honmei
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    Mud pond and Back yard recirculating system are two totally different things with two totally differnt set of dynamics and correlating a comparison is totally out of whack. Mud ponds are deeper and simply larger with lower stocking densities. Movement of waste to filtration for removal does not exist in a mudepond.

    Thus in backyard recirculating systems current are used/even needed to compaensate for the differences between "nature" and our backyard recirculating systems.
    The views presented are my personal views and not that of any organization that I may belong to unless otherwise specified. [email protected]
    CKHPA

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