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Thread: Rocks / gravel

  1. #1

    Rocks / gravel

    Afternoon all,

    Hope your all well in these turbulent times.

    Donít want to throw the cat amongst the pigeons but I just wondered if any members had any experiences good or bad with rocks / gravel on the bottom of koi ponds etc?



  2. #2

    20+ years ago I tried a filter made from a tray with gravel and a series of drilled push fit pipes - the idea was the water would be drawn through the gravel - it worked for a while - until the gravel got full of muck and then the koi kept digging into the gravel releasing the muck - my idea came from a tropical fish tank I had in the house with air riser. The tropical fish worked great as they didn't route about in the gravel. It was a total pain to clean as the pond needed to be drained to access the gravel / tray and washing it in buckets was very time consuming.

    Far better filters about nowadays for koi.

    Probably great in a wild life pond with a waterfall - probably not a good idea for koi who love digging up the bottom


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  4. #3
    I can tel you what the next 5 posts will be lol

    Donít do it.
    Too many nooks and crannies which will result in nasty bacteria lurking.
    Same as folds and crease in pond liners, nasty, smelly places.

    Wouldnít dream if doing it myself just in case that is actually true but itís been written by so many experienced pond keepers previously it more than likely is.
    If you think about it logically, It stands to reason that poo on the pond base wonít be a good thing, it needs to get sucked down the bottom drain and out of the system ASAP, rocks and crevices on a pond bottom will hinder that process without a shadow of a doubt. It will be left there rotting and festering.
    A pond isnít a natural lake that might have millions of gallons of naturally filtered water to keep it in check, itís a very small puddle in comparison so waste needs to be eliminated.

    Sent from my iPhone using Tapatalk

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  6. #4
    Ask an honest owner of an Aquascape type pond with a population of koi (pond liner with 100% gravel bottom, zero bottom drain, and a skimmer installed at one end of the pond, feeding overflow and surface scum through a large upflowing gravel filter bed) and they will admit that they need to very thoroughly clean their pond bottom and the upflowing gravel filter at least once a year (in order to thoroughly clean a pond full of gravel, one really needs to transfer the fish to a tank, empty the pond dry, and gently jetwash all the gravel and pond liner). It's a massive stinky, gross job to look forward to, at least once, every single year. Well installed, and of a suitable size, the upflowing gravel filter can provide surprisingly clear water, but that kind of set-up is inevitably fighting a losing battle with the endless solids and fines a koi population excretes, especially considering that domestic koi ponds are 'closed systems' (with an unnaturally high mass of fish in relation to the mass of water in the system) with rather minimal water changes (if any!). Even with optically clear water, there is no guarantee that the accumulating solids and fines won't ramp-up ammonia levels (admittedly, one could argue that the gravel strewn over the entire pond bottom might compensate for this, by increasing nitrification, by harbouring larger populations of healthy bacteria, but there is no guarantee that levels of pathogenic bacteria won't also be harboured by the gravel).

    It's interesting to note that Reinhold Borsch has used river pebbles in some of his high-end ornamental koi ponds (*it might be that he took certain technical measures to avoid problems, which may not be visible to someone without visiting the pond in real life. Additionally, it's noteworthy that this pond is 510,000 litres, with less than 20 fish visible, so that's an extremely low stocking density).


    but he clearly chose not to use river pebbles in this project:


    I don't know if this was an ongoing change of approach adopted by him, or if it was just a specific client request to build a smooth GRP pond instead of pebbled. The pebbled bottom looks very traditional and 'natural', but I still think pebbles and gravel lining a pond bottom pose unnecessary risks in 98% of circumstances (that remaining 2% is an interesting topic in itself, but too much to get into, here). Even without the risks, who the heck wants the stinky job of cleaning rotting solids and mulm from their pond once or more every single year?

    So, I'm with bigcarpchaser, on this one. It's generally better to play it safe and avoid the unnecessary health risks (and maintenance chore) of a gravel pond bottom, unless you place a higher value on pond aesthetics than you do on the health of your koi (in which case, it's morally questionable if one should be keeping koi at all). If you only intend to keep a very small number or mass of fish in relation to the volume of water in your pond system, you could possibly relax slightly on this point, but it's still not the best approach. I don't mean that in a judgmental sense - it's just from a pragmatic standpoint. Do you use a mobile phone whilst driving? Do you drive without wearing a seatbelt? etc. etc.

    However, that's only my opinion, and other pond owners may vehemently disagree.
    Last edited by MustBeSomethingInTheWater; 06-06-2020 at 11:32 PM.

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  8. #5
    Extreme Koi Member Rank = Kyusai 1meterchag's Avatar
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    Aug 2012
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    I totally agree with the above posts!!

    Gravel filters are basically breeding grounds for anaerobic bacteria and should be avoided.

    Koi ponds need to have clear, benched bases leading to a bottom drain on pipe work that can be purged.


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  10. #6
    Senior Member Rank = Gosai RipleyRich's Avatar
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    I would never do it in my pond, but just offering the counter argument that we do it in Aquariums.

    The difference is, we can see build ups of detritus and syphon it off.

    As others have said, it`s a risk so why take it?

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  12. #7
    Senior Member Rank = Nanasai davethefish1's Avatar
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    Apr 2019
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    under gravel filters were standard items used in aquariums from koi ponds to reef tanks in the 70's and 80's even into the 90's.
    and a horiffic amount of fish used to die in home fish tanks on a scale that we would just not accept today.
    we know what new pond syndrome is but they also had 'old tank syndrome' where there was so much crap in the filter the entire tank would go septic and get wiped out.
    the amount of crap they used to hold was truely unbeliveable, unless you've actually cleaned one out that had run for a year or two...

    things move on and are improved,
    undergravel filters were only really popular in aquariums with very light biological loads like marine tanks, and planted tropical tanks with very small fish.
    that used plants or critters to consume decaying organic material in the gravel/sand.
    Last edited by davethefish1; 07-06-2020 at 10:28 PM.
    The Solution to Pollution is Dilution

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  14. #8
    Evening all.

    Thanks for all your input and advice, itís pretty much what I thought ha ha



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