Thread: Lost one of my 3 Koi on Wednesday (21/01/2026)

Got all 3 in 1998 as tiddlers from local garden centre to reteach the goldfish to come up for food after they had had a heron scare. All went well and they grew to a right old size. 70cms ish. We even re-dug out a pond to make it bigger and deeper to survive the winters.
Last wednesday I went to check on them after the very cold overnight temperatures and Dyson ( food guzzler) had surfaced and was in one corner of the pond looking frozen and terrible condition . Too long a story to tell but after a battle we finally lost "him" ( presumption) this wednesday.
One of his siblings is also looking bad but not as bad as he did and has started to shed a bit of his slime coat after being treated for 5 days with anti ulcer / bacterial treatment in the pond. He stayed with Dyson, side by side for most of the week and was next to him at the bottom when I had to haul the last gasp of Dyson out of the bottom of the pond. The third Koi has always been a little more distant from the larger 2 and looks ok and is staying with more normal pond position for this time of year , despite the pond treatments and the slight commotion at times .
Fish Keeping is hard and I am feeling really sad to have lost one of the 3 after sooooo long trying to keep them all healthy and safe. Frankly torturous at times. We had one emergency run to the vet once when a ulcer on no 2 punctured all the way through and had pond water slushing around his innards.... you just wouldnt have believed it ,,, hole the size of a 20p piece. Vet put iodine in and plugged it with an oral gel filling... That was 6 years ago and he's the one hanging on tenuously now. Cold weather coming, cold nights at any rate..... we are bracing ourselves .... good luck all when this spring finally comes and we see how all have faired through this weird up and down winter.

Sorry to read this, after so many years they definitely become part of the family, kids are born, grow up and leave home, and the Koi are there throughout the entire journey, so I can imagine that it is difficult to see this happening.

Considering the time of year and the age of the pond, it is worth checking the pH and KH to make sure they haven't been killed by a pH crash, more so considering the amount of rain we've had. I feel that pH crashes seem to be a common cause of Koi deaths at this time of year, simply because we do less maintenance and water changes in winter, more so on long established ponds where you tend not to keep such a close eye on parameters because the pond usually looks after itself.

Have you done a pH and/or KH test?

Thanks for reply… second koi …. Had his last day today. Yes … ph was ok but nitrite was up … one is left and looks ok and all normal pattern of pond swimming and depth stays at the moment … they def both had a fungal issue which we tried to treat but too down on immune system … well that’s one theory anyway … we had a lot of birds coming in for water during the end of year dry spell despite bird baths elsewhere. Not sure if that has added an extra sickness potential. Some 27 years for the 2 of them and some scary times in that . Will miss them immensely popping up for food at every possible opportunity when they caught sight of you anyway near the decking. But probably just goldfish for a while! south uk weather just too variable these days too.

Very sorry to hear of your problems, I always think it is worse when you do not know what the problem is, such a shame, continue to enjoy your pond, I hope you will grab another couple of Koi n the future, they sure liven up a natural pond I feel

Originally Posted by dbs

Very sorry to hear of your problems, I always think it is worse when you do not know what the problem is, such a shame, continue to enjoy your pond, I hope you will grab another couple of Koi n the future, they sure liven up a natural pond I feel

I am reviewing all in spring . 1 koi left . Looking ok apart from very mucous covered eyes. Trying to work out if all is ok or if whole pond needs a deep clean from professional company . If it was white spot and fungal infection leading to septicaemia ( looking at the 2 out of pond At the end ) the medication treatments may not have sorted the pond out .
any inputs / opinions welcomed for next steps and for remaining koi management .
I never really planned for fish …. Legacy from my dad !

What was the actual pH reading and what test kit did you use?

Also what were the other readings you took, nitrite etc?

My instinct would be that this is a water / maintenance related issue, not excluding bacterial issues through sludge etc.