Newbie question


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We have quite a large clay bottomed pond( 30k gallons) which is stream fed from a tiny run off from a cattle filled field. We have 2 grass carp around 26 cms long plus a large Koi carp and 2 mirror carp plus 7 -14 cm Koi and around 16 small koi and goldfish.
We have been testing the water for everything including its salinity and all the stats indicate it is an healthy thriving pond even the lilies and the marginals are flourishing.
The reason we are worried is that we have lost 5 mid sized Koi,1 small koi,1 small goldfish all within the last 6 weeks.We noticed one of the fish had ulcerations on its face but most of the others looked perfect with no heron damage or other predation having taken place. We bought two different solutions to clear bad bacteria, pond bombs etc and other good bacteria solutions,we have also incorporated 25 kg of salt which has increased the salinity to 0.02 so the pond should to be in good condition.The large fish are all healthy its just the 14cm koi that seem to be dying off and I am totally clueless about what to do next.The pond does not have a filter, water runs in slowly or quickly when it rains and pours out over an overflow set 2 meters high so the water level will double its depth on very wet days.

We wondered after reading various forums if it was the norm to constantly lose fish as so many pond keepers seem to have the same problem.The mid sized koi are a joy to watch and are buzzing around eating everything they can.We have noticed some water is leaking through the bank which has lots of tree roots in it but that cannot do much harm,We use bentonite powder to try to block the holes up.We wondered if the farmer was using nitrogen on his land and we got a lot of nitrate through the stream but our pond testing laboratory is still stating everything is ok, the ph level is 7.5 and there is no ammonia to be concerned about.

Can anyone think of anything else we are missing or should we just accept this number of losses?
 
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Jhn

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When the tests came back what are the numbers? Any pics of the pond? It is definitely not normal to lose fish constantly.

if you are having run off feeding into the pond from nearby fields that in all likelihood is the issue. If the farmer uses fertilizer, any type of chemical spray, etc. will end up in the pond when it rains. Going to be tough to control that outside of creating a large wetland/ bog area where the stream enters the pond so the wetland area catches the run off before it gets into the pond. Wetlands in nature basically act as kidneys for the aquatic systems in which they are connected.

I wouldn’t add salt to the pond anymore, as it can end up killing the plants, which in a large unfiltered pond is the filter. If any Fish are showing signs of distress I would try removing them to a separate tank set up with pond water and test them in there. Also, if the pond has a constant flow of water through it you won’t be able to maintain a consistent salinity level, anyhow.
 
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Joined
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When the tests came back what are the numbers? Any pics of the pond? It is definitely not normal to lose fish constantly.

if you are having run off feeding into the pond from nearby fields that in all likelihood is the issue. If the farmer uses fertilizer, any type of chemical spray, etc. will end up in the pond when it rains. Going to be tough to control that outside of creating a large wetland/ bog area where the stream enters the pond so the wetland area catches the run off before it gets into the pond. Wetlands in nature basically act as kidneys for the aquatic systems in which they are connected.

I wouldn’t add salt to the pond anymore, as it can end up killing the plants, which in a large unfiltered pond is the filter. If any Fish are showing signs of distress I would try removing them to a separate tank set up with pond water and test them in there. Also, if the pond has a constant flow of water through it you won’t be able to maintain a consistent salinity level, anyhow.
Hi,
The tests state the salinity is still on the low side the ph is 7.5 which is good, the nitrates and nitrites ammonia were all spot on the recommended levels.The stream runs through a dairy farmer's field through a pipe under the lane outside into the garden down a reedy deep trench for 100 yards into my pond, the pond empties via an overflow when it gets up to 4 foot deep it can drop down to two feet in summer as water tends to sieve through the clay into the lower part of the outlet pipe.The plants are extremely healthy and I have used various bio treatments to prevent any further deaths and fortunately there haven't been any more since July.

You may be correct regarding foreign chemicals entering as the pond is at the bottom of a slope where the waters congregate after a rainstorm and there could be a case that the farmer fertilises his sloping fields with nitrogen,I have also noticed some oil floating on the water at times this is either from the lane that runs across the slope or off my ride on mower which seems to need hydraulic oil top ups a lot these days but I cannot trace a leak.
Regards
John
 

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