also, if the pond is outdoors, have you had much rain lately? if it's not properly banked, you could be getting runoff water coming in, which could carry all sorts of toxins and irritants (fertiliser, weed killer, pesticides etc) from the grass to the pond which could be killing them off.
So remember, when you're feeling very small and insecure,
How amazingly unlikely is your birth,
And pray that there's intelligent life somewhere up in space,
'Cause there's bugger-all down here on Earth.
Loki/Grendel/Gail/Beowulf/Camilla/River/Bathory/Arwen/Lafayette/Deb/Jack Skellington (soon)