"Lee Brouillet" wrote in message ...
I will bet dollars to donuts that you either have a rock bottom to your pond
or several inches of gunk that has accumulated. If so, your pond needs
cleaning badly. If the hydrogen sulfide is as bad as you say, then the fish
will have to be removed while the pond is cleaned or they will die.

Please give more detail about the condition of the bottom of your pond.

Lee


Thanks for your reply and the others who suggested H2S. I haven't read
this newsgroup for a while (because of computer problems, reinstalling
Windows etc.) but I have already drained the top pond and cleaned out
about 15cm depth of slimy mud, and refilled it. In the process I found
three fish still alive (and loads of frogs) and transferred them to
the lower pond, where I think they are still OK. I think the next task
is to check for water leaks around the waterfall area so I can leave
the pump on all the time without having to top up too often.

Mike.