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Sorry, everyone, I've only just checked this section again and hadn't realised that there'd been so many more replies.
Many thanks for all your helpful suggestions. I think the main problem is my being impatient, particularly now that I've also constructed a small rockery just above the pond and want to get plants in there too....I will try the barley straw and leave the rest to nature.
My next door neighbour has a more mature pond, so I'll ask her if she can spare a bucket of water. At the moment there's nothing in there for the newly-resident newt to eat, so it seems like a good plan. I'd love to have fish, but the cats and a local heron would get them. And the first frogs have started to arrive.