Large garden pond, 8 fish, Koi have died over the past week.

[Total loss]

As in title, my parents Koi fish started to die a week ago, some of the 'small' ones first, 6 inches long & apparently they have found one of the big ones 1 foot long dead this morning.
The pond is 40+ years old, waterfall, filter & uv lamp,they have never had a problem before & they have got a couple of very big Koi in there, 18 inch plus.
What to do, are there water test kits? take a water sample somewhere?
Any other possibilities?

[CAPP0]

Yes there are water test kits, you take a sample and add different chemicals to test for different conditions. I'm no expert but a good friend has a large koi pond which I sometimes look after for him when he's on holiday, that's how I know the little that I do!

I know he's paranoid about certain substances being in the water, sorry but I can't remember which. Possibly ammonia?

Speak to a good koi shop and get a test kit, they're £20-ish iirc and will last a long time.

[Total loss]

Thanks, I'll look one up.
No changes have occurred/happened, if they had it would have been at least a starting point.

[Total loss]

Update
They took a water sample from the pond to a local pond/fish specialist this afternoon, as they would test it for them, test result shows the water is perfectly good.
I asked what other suggestions they were given if not the water? apparently no idea.

[anonymous-user]

Sorry to hear of the loss. Which tests did the shop do?

[Russ35]

More than likely a parasite. Something like Ich (white spot).

We had a bad case of it last winter, lost 5 or 6 koi including a 3ft sturgeon. Water quality was all ok on the test kit. Took a fish to our local place and they did a scrape on the fish and put it under the microscope.

I think we just salted the pond. x lb of salt per gallon or something like that. Did that 2 or 3 times over 10days. There are chemicals you can get to treat parasites, but most of them require the water temperature to be over 10deg. So this time of year your limited to what you can do, unless you heat the pond.

Edited by Russ35 on Saturday 13th March 20:28

[Blue32]

Had a similar experience a few years ago, ended up moving the surviving fish to a large tank and draining the pond where we found a dead toad in the bottom of the pond. So assumed as it decomposed it must have poisoned the water.

[Total loss]

flashbang said:

Sorry to hear of the loss. Which tests did the shop do?

I'll find out

[Total loss]

Russ35 said:

More than likely a parasite. Something like Ich (white spot).

We had a bad case of it last winter, lost 5 or 6 koi including a 3ft sturgeon. Water quality was all ok on the test kit. Took a fish to our local place and they did a scrape on the fish and put it under the microscope.

I think we just salted the pond. x lb of salt per gallon or something like that. Did that 2 or 3 times over 10days. There are chemicals you can get to treat parasites, but most of them require the water temperature to be over 10deg. So this time of year your limited to what you can do, unless you heat the pond.

Edited by Russ35 on Saturday 13th March 20:28

Thanks, I'll look into that possibility

[Total loss]

Blue32 said:

Had a similar experience a few years ago, ended up moving the surviving fish to a large tank and draining the pond where we found a dead toad in the bottom of the pond. So assumed as it decomposed it must have poisoned the water.

No possibility of a toad/anything else getting in due to the small mesh anti heron net.
I don't know how long since the pond has been cleaned out, is it something that should be done every X number of years?

[otolith]

Are the fish showing any abnormal behaviour?

[Drive it fix it repeat]

Fitting name OP, we had a similar problem and lost some nice fish including a few koi. Turned out to be a heron visiting at day break, bd.