rain dissolves a lot of CO2, which becomes a mild acid. it is usually
pretty warm and there isnt much O2 in the rain water. oxygenating
plants give oxygen during the day and use it up at night.
big fish going first is a problem with getting enough oxygen, either
in the water, or attack on the gills by toxic water or parasites.
Ingrid

On Sat, 23 Jun 2007 16:29:41 +0100, "Carole"
wrote:

Thanks for this Ingrid,
I'd be surprised if it was an oxygen problem - temperatures here in the UK
are low for June - and we've had torrential rain for most of the month. I
have a waterfall, and loads of oxygenating plants to keep the oxygen level
up. But I agree, it's strange that it's the bigger fish that have died (I
would guess they're about 5 years old). I assume that is there was a
'poison' problem the little ones would have gone first.
Now I think of it - I found all the bodies next to the piece of wood, but
assumed they had been washed there because the input flow is at the opposite
end. Maybe the larger fish had been nibbling at the wood and it had
something in it which killed them, rather than my initial thought that maybe
the wood had leached something out.

Well I've removed the wood now, so I can only wait and see.
Thanks for your reply.

wrote in message
.com...
the key is "the larger" fish died. this is almost always a sign of
problems with enough oxygen. oxygen problems occur as water temps
increase. they die in the early morning hours. at any time you see
fish at the surface "piping".
otherwise, it could be a disease attacking the gills. it could be
toxins, so do take the board out of the water and only use plain pine
in the water. you dont have any yew trees or bushes around do you?
yew is extremely toxic, sometimes the berries drop into the water.

the other think it might be is infection of egg bound female fish. you
would need to do a necropsy and see if the egg sacks are yellow... any
color but clear/white.
http://weloveteaching.com/puregold/d...e/gf_anat.html
Ingrid




On Sat, 23 Jun 2007 11:24:08 +0100, "Carole"
wrote:
I have a mature pond about 8 years old, 800 gallons, about 50 goldfish
ranging from tiny tiddlers to about 5" long, plus one really big ghost koi
about 18" long. I have all the usual filtration, waterfall and
oxygenating
plants, UV light, water is nice and clean and clear and always has been. I
feed the fish about every couple of days - if they get too much they get
frisky.

Big problem - In the last week I've found 3 of the larger goldfish just
floating dead in the water. They have no signs of any disease and look
perfectly OK, just dead.