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    Results 21 to 23 of 23

    Thread: Lost 50% of my koi over last 7 weeks... flukes?

    1. #21
      kdh is offline Senior Member
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      Join Date
      Feb 2011
      NW Arkansas
      Did you ever take readings of your water before the problem? If so what were they?

    2. #22
      SJK is offline Supporting Member
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      Join Date
      Aug 2020
      Gig Harbor, WA
      Since you've had a vet identify a fluke problem but nothing else let's go back to some basic water quality issues:

      1) Have you added any new fish in the last few months? Do any of the fish that have died, or are ill, have a notch across their nose? The vet didn't find signs of costia, but it and KHV tend to kill large numbers of fish quickly. So if they have notched noses and new fish were added, it could be KHV. As RTB noted, the salt should have killed other parasites. An FM&G treatment normally might be warranted if the fish are strong enough to handle it, but since the vet didn't find other ones, its back to water quality issues.

      2) Your water quality shows traces of ammonia, nitrite and nitrates. The ammonia and nitrite readings of 0.25 (your possible high end) indicate the bio-filters may not be not keeping up with the fish load, so two issues to explore here.

      First, a 20,000L pond is about 5,300 gallons which would support 530" of fish max at 10 gallons per inch of fish. The pond had a minimum of 720" using a calculation of 40 fish at an average 18" per fish (avg of 30-60 cm). So it was ~35% overstocked. In early years not a problem but as fish continued to grow, the filtration system may have hit an overload problem. If your water quality looks poor (dull/not clear, etc.) and your ammonia and nitrite reading keep increasing, it indicates the filtration system may not be keeping up. (Sadly, having lost 1/2 the fish, the load is now about 360" so the filters may catch up going forward if this was a problem.

      Second, you mention having a set of Japanese mats as the only filtration. Does this serve both mechanical (removes leaves, poop and debris) and bio-conversion (houses the nitrifying bacteria) filtration? And what is your filter maintenance practice? How often you rinse the Japanese mats? The system may have built up over the last year to where it is overloaded and is no longer functioning properly. It would help to know what your regular maintenance practices are. You mentioned frequent water changes, which is excellent. Do you want to come in from a well or is it tapwater?

      And finally, as this has us all puzzled, what is the length, width and depth of your pond and what kind of shape is it? You mentioned it only has the one water return from the filter area. As it's a good size pond, it's possible that the water circulation in the pond is leaving some areas of water stagnant. I checked the air temperature in Sydney and it's a beautiful 80 on average, so it doesn't seem like water temperature would be an issue.

      I'm sorry you're experiencing these losses. As a new pond owner (inherited with house) myself, it would be devastating to lose beautiful fish in an established pond despite the work you're doing. Please keep us posted.

      Last edited by SJK; 1 Week Ago at 01:00 AM.

    3. #23
      coolwon is online now Senior Member
      is Garfield is my name DIY is my
      Join Date
      Feb 2016
      Durban South Africa
      You added air and stones to your pond?

      Would that have been before or after the loss of the fish?

      Are you still losing fish?

      I presume you use sodium thiosulfate when you do your water changes, and wash out the Japanese filter matting using your pond water to preserve the inhabitants.

      Find more about Weather in Durban, ZA

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