Hi all,
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 (comprises two large drums
containing filter
brushes and 'foam' pads - these are cleaned 2-3 times a year), waterfall and
oxygenating
plants, UV light, water is nice and clean and clear and always has been.

There is a drain/filter at the bottom of the pond
which takes out the water and feeds it through the filter system and back up
into a small top pond, over a small waterfall, and back into the main pond.
I feed the fish about every couple of days - if they get too much they get
frisky. I top up the pond every few weeks, as and when needed due to
evaporation,
from a tap and use a water conditioner at the same time.


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 otherwise, just dead. This is very distressing as I'm
spending every
moment checking the pond and expecting all my little friends to die. I put
some medifin in the pond a couple of days ago (I treat it twice a year
normally - Spring and Autumn), but I've had another death since then.

The only thing that's changed recently (don't know if it could possibly be
the reason) - I recently netted the pond because we were visited by a heron,
then I realised that the frogs and newts couldn't get in and out so I put a
length of wood into the water from the side. The wood is sapele (sp?) and
is definitely untreated, but I know some hardwoods have funny substances in
them - do you think this might have poisoned the water ??

I've removed the wood now of course.



I have pond test kits and use them regularly - recent tests (a couple of
weeks ago) gave the following results :
- Ammonia less than 0.1 - no problem
- Nitrate zero - no problem
- PH 8.5 - acceptable.

Thanks for any help, Carole