Thread: Loss of Koi - cold related?

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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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?

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.

...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

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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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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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.

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.

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.

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.

2 degrees change a day is pretty safe