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  1. #1

    Loss of Koi - cold related?

    Last weekend all the Koi were swimming about quite happily and still eating a little. Polycarbonate covers were put in place last Sunday and when we lifted the covers yesterday we found 6 dead Koi + goldfish + 2 that were so far gone we had to euthanise.
    Before the big clean up yesterday I tested the water and even the nitrite was showing 0 whereas it’s normally 0.25 (new pond syndrome). Ph has dropped from 7 to 6.5 but other than that nothing else appeared to be wrong.
    I am honestly devastated and if we hadn’t already got a new filter system drum + combi on order I would be tempted to give up. It’s been a tough year and so many difficult learning curves.

    We really need to get heat to the pond and keep it to a minimum of 5 degrees but our household wiring is old and would not cope with anything high wattage. It is being replaced next year but we need something to tide us over.
    Does anyone have experience of an LPG water heater or similar?
    The pond is part in ground and part out with a volume of between 16,000 and 18,000 litres.
    Any ideas would be much appreciated.



  2. #2
    Senior Member Rank = Mature Champion Twhitenosugar's Avatar
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    Hi sorry to hear about your losses.

    Do you think you lost fish due to a pH crash, rather than the sudden drop in temperature?

    The fact you noticed such a big drop in pH may suggest that was the case.

    What was your kh? If that was zero you probably had a pH crash.

    Also when did you last do a water change.

    As people tend to do less water changes in winter, that is when people are more likely to be caught out by a pH crash.

    I would look to up your ph to protect your existing fish. You can do that either with a few partial water changes, spaced out (providing your tap water has some kh) or if you have really soft water, still do a water change but add half a mug full of bicarb of soda to the water to increase the kh, which will then buffer against pH swings.

    When trying to up the kh/pH make sure you do it gradually rather than in just one go. But it's important you up it a bit, quickly, to protect your remaining fish.

    In answer to your point about heating, I would suggest getting a couple of 600watt titanium aquarium heaters.

    They are fairly cheap to buy (about £60 each from what I recalled I paid), are easy to use i.e. plug and play, they are more durable than the glass ones, they're not that long so you can just drop them into your filters, and with a wattage of 1.2kw should be ok (if they're not then maybe just keep one running to reduce the load on your electrics).

    On your sized pond, they won't make it super warm, but will be able to notch up the temp by a few degrees, especially if it's insulated in cold spells.

    You will need to get a thermostat for them. I use an inkbird one (available from the likes of Amazon and eBay) which has worked reliably for a number of years for me on my grow on tank in my garage.





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    Last edited by Twhitenosugar; 25-11-2024 at 02:32 PM.
    13,000L fibreglassed raised pond with window

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  4. #3
    Senior Member Rank = Adult Champion Alburglar's Avatar
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    Chineses 500w stainless heaters are a tenner each on eBay. The brand Hidom is the make I have and they are great..
    Plus a cheap temperature controller and a weather proof box.
    Have a look on my build thread.
    What temps did the pond get down to?
    2660 Gallons. 4" Bottom Drain and Skimmer. Draco Solum 16 Drum. Anoxic Filtration. Air lift returns.

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  6. #4
    I have a pond of 13,000 litres and it's not covered or insulated in any way.
    It is fully in-ground which does help considerably, but during the recent cold snap it did drop to about 5C.
    As this was only for a few days the fish did slow down and stop feeding but have been absolutely fine. The Koi range from 22-28".
    I have 4 x 600W drop in heaters which I drop in the filter system over Winter. These are controlled by a thermostat and come on at 5C. I don't try and heat much above this temp.
    I only cover our pond in prolonged cold freezing weather, and being an irregular shape use a floating swimming pool cover - so less forgiving than usual covers and I've never had any issues. Aeration/gaseous exchange isn't an issue due to the large filter and air lift.
    Soooo, with all that I am going to second 2WNS in suggesting that temperature would not be top of my list of suspects.
    A pH of 6.5 is suspiciously low and so I also would check KH.
    These days KH is the only thing I ever really test for.
    My DIY ponds from 1988 until present day.
    All can be found here:
    https://www.ukzero.com/pond.htm

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  8. #5
    Thank you for your reply.
    Did consider pH but thought 0.50 difference was too little to make a difference but it could have been that. I didn’t check kh this time but it’s usually between 2 and 3. We have very soft water in Cheshire.
    After putting the polycarbonate sheets on I didn’t test the temperature until the weekend by which time it was around 9 degrees. Ordering a remote thermometer so I can keep a proper check.
    Will definitely order some heaters and increase the polycarb from 10mm to 25mm. Next year we will install an air source heat pump as I couldn’t face numerous losses again.
    Again, thank you for your advice.

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  10. #6
    Will definitely look at your build and the heaters will be ordered. After the polycarb sheets went on last week, I only checked the temperature this weekend and of course it was warmer then.
    Thank you for your help

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  12. #7
    Senior Member Rank = Adult Champion Alburglar's Avatar
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    ...it got covered more recently on another thread, with eBay links too:

    https://www.koiforum.uk/koi-pond-equ...ontroller+temp

    However,
    First port of call, would be checking ALL parameters,
    If your kh is low the drop in ph could indicate the start of a crash as twhite... Suggested. That, combined with a cold stint may have been easily avoided and easy to solve. The fact that goldfish died too is pointing towards water issues and away from parasites but if you find nothing further wrong with the water, it's the second port of call to scrape a fish.

    Steep learning curve with koi, but plenty of resources here to help.
    But without water parameters, its not possible to give sound advice
    Last edited by Alburglar; 27-11-2024 at 03:35 PM.
    2660 Gallons. 4" Bottom Drain and Skimmer. Draco Solum 16 Drum. Anoxic Filtration. Air lift returns.

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  14. #8
    I appreciate that kh is important too and I have perhaps not tested that as often as I should. Our tap water is just over 7 and using the API test kit the pH has always been 7. Thinking of trying some of the Kusuri seaweed to increase these parameters as it’s supposed to protect the levels for 12 to 18 months. To help counteract the lack of viewing Koi activity with the covers on I’ve installed a pond camera so I can check on them anytime. Thanks again.

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  16. #9
    Senior Member Rank = Mature Champion Twhitenosugar's Avatar
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    Denise, what have you actually done with the pond since you discovered the dead fish? lts not clear if you have you carried out a water change or added any bicarb?

    If you haven't done so, I would asap.

    The bacteria in your bio filter use up the kh in the water when breaking down ammonia and nitrite. And once the kh is used up the pH can start swinging about. And it doesn't take too big a change of pH to wipe out your fish.

    So if you haven't done any of the above or tested for kh, then I suggest you do so immediately, otherwise you are at risk of losing more.

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    Last edited by Twhitenosugar; 25-11-2024 at 11:42 PM.
    13,000L fibreglassed raised pond with window

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  18. #10
    Quote Originally Posted by Twhitenosugar View Post
    Denise, what have you actually done with the pond since you discovered the dead fish? lts not clear if you have you carried out a water change or added any bicarb?

    If you haven't done so, I would asap.

    The bacteria in your bio filter use up the kh in the water when breaking down ammonia and nitrite. And once the kh is used up the pH can start swinging about. And it doesn't take too big a change of pH to wipe out your fish.

    So if you haven't done any of the above or tested for kh, then I suggest you do so immediately, otherwise you are at risk of losing more.

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    Immediately after finding the problem we did a 30% water change through the HMA unit. As we had found dead fish we also used Virkon aquatic in case of bacteria from the dead fish. The aerated retro bottom drains were also flushed out and cleaned. This morning we are going to add some bicarb and kh test this evening. I genuinely did not realise that what I considered a small drop in pH could have made such a huge difference. I feel so guilty! Just in case I have ordered 25mm polycarbonate

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    Senior Member Rank = Mature Champion Twhitenosugar's Avatar
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    Ah, glad you did a water change.

    It's possible it wasn't a pH crash. But the fact your ph dropped is an indicator. And the drop test kits aren't always that accurate, so it could've dropped more than the drop test suggests.

    Plus I recall others on here having pH crashes in similar circumstances, so I had that in the back of my mind.

    If you have soft water, it's probably worth buying a big tub of bicarb. It's not that expensive, lasts ages and is handy to have.

    Hopefully there is nothing else going on in the pond, and that's the end of your woes.





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  22. #12
    Extreme Koi Member Rank = Supreme Champion john1's Avatar
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    Sorry to hear of your losses Denise you must be gutted.

    Agree with all that has been mentioned,kh in my book is the most important check to do and as I have very soft water I have to add sodium bicarb quite often so buy a 25 kg sack of it as it's cheaper that way from Ebay.

    Cold wouldnt have killed them but kh can.
    Rain water has very low kh and that goes in your pond so you need to keep an eye on it.

    Hope it all works out for you Denise.
    John

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    Senior Member Rank = Mature Champion smartin's Avatar
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    Also sorry to hear of your losses, everything points to a PH crash from what i have read and agree with all the responses you have had, try to move on from it, some very experienced dealers have lost fish to PH crashes / lack of oxygen etc, there are so many factors to keep an eye on......
    I assume you had some air gaps in your covers, again even with air pumps running you will get a build up of gasses above the waterline and could be dangerous to the fish, but it would have to be nigh on air tight to be a cause but worth checking.... i test my KH weekly, its surprising how quickly it drops away once it starts...... atb Steve.
    2200 gallons,infinity window,
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  26. #14
    Quote Originally Posted by john1 View Post
    Sorry to hear of your losses Denise you must be gutted.

    Agree with all that has been mentioned,kh in my book is the most important check to do and as I have very soft water I have to add sodium bicarb quite often so buy a 25 kg sack of it as it's cheaper that way from Ebay.

    Cold wouldnt have killed them but kh can.
    Rain water has very low kh and that goes in your pond so you need to keep an eye on it.

    Hope it all works out for you Denise.
    I was honestly devastated. I felt numb. To see these beautiful creatures lose their lives because of something I have done or not done made me feel sick to my stomach. The pond video camera has now been in a couple of days so at least I can keep an eye on them. The best of it is we have a 25kg bag of bicarbonate so if it was the pH we could have prevented it.. Huge lesson learned. Thank you for caring.

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  28. #15
    Quote Originally Posted by smartin View Post
    Also sorry to hear of your losses, everything points to a PH crash from what i have read and agree with all the responses you have had, try to move on from it, some very experienced dealers have lost fish to PH crashes / lack of oxygen etc, there are so many factors to keep an eye on......
    I assume you had some air gaps in your covers, again even with air pumps running you will get a build up of gasses above the waterline and could be dangerous to the fish, but it would have to be nigh on air tight to be a cause but worth checking.... i test my KH weekly, its surprising how quickly it drops away once it starts...... atb Steve.
    Only people who own Koi ponds could understand what it feels like to lose them. We do have air gaps in the polycarb and for peace of mind I’ve dropped an Inkbird thermometer in the pond this evening so the temperature can be monitored. KH will be tested every few days now. Thank you for caring.

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  30. #16
    Senior Member Rank = Adult Champion Alburglar's Avatar
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    Denise, are you anywhere near Welwyn Garden City, someone on the for sale section needs to re-home some koi quickly due to a leak. You may be able to replenish some stock before the temps really drop.
    2660 Gallons. 4" Bottom Drain and Skimmer. Draco Solum 16 Drum. Anoxic Filtration. Air lift returns.

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  32. #17
    Quote Originally Posted by Alburglar View Post
    Denise, are you anywhere near Welwyn Garden City, someone on the for sale section needs to re-home some koi quickly due to a leak. You may be able to replenish some stock before the temps really drop.
    Wish I was it’s warmer in the South. Thank you for letting me know but I’m in Cheshire. Hope the person gets sorted that’s such a shame 😔

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  34. #18
    Touch wood remaining Koi seem to be okay.
    A further question please. We moved the Saragoi last weekend into the VAT as we felt she was vulnerable because of recently healed ulcers The Vat is heated to 15 degrees. What is the best way to transition her from the heated tank bank into the pond? The pond is currently at 5.7 degrees. It's lonely for her in there too.

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  36. #19
    Extreme Koi Member Rank = Supreme Champion john1's Avatar
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    You need to slowly drop the temp in the vat Denise, when you get matching temps then ok to move.
    I find they dont take well moving from warm to cold,but better from cold to warm,know this doesnt help you much.

    May take a while to match the temps though.
    John

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  38. #20
    Senior Member Rank = Adult Champion Alburglar's Avatar
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    2 degrees change a day is pretty safe
    2660 Gallons. 4" Bottom Drain and Skimmer. Draco Solum 16 Drum. Anoxic Filtration. Air lift returns.

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