On 01/10/2013 10:39, Sacha wrote:
Oh dear, our two largest fish have died. Each was well over 1' long.
The pond pump has broken and another is on its way but we think it must
be lack of oxygen that's caused it. Ray played a hose over the pond
for a long time but obviously, it wasn't enough. It seems daft to be
upset about two dead fish but they used to give children such a thrill
when they glided up to be fed.

....to say nothing of what fish that size would cost to replace. How big
is the pond? Have the fish perhaps outgrown it, and the oxygen levels
fallen below what they require? It's usually stated to be about 1
square foot of surface area for each inch of fish.

All you wanted to know about pond aeration (and a lot more you didn't!):
http://www.fao.org/docrep/x5744e/x5744e0m.htm

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Jeff