In article , Robert Wallace gerbil@bo
bwallace.glowinternet.com writes
I have a small pond I keep for frogs and wildlife.
Each year it gets covered with a thick layer of duckweed that causes the
water to become dark and evil smelling.

It's not the duckweed that is causing your water to be dark and evil
smelling!! If anything, the duckweed will help it not to.

I asked my local fish and pond centre for some magic powder, but they said
all you can do is scoop it out.

It's true.

This is plainly ridiculous as it grows faster than I can scoop!

Nope - you just don't do it often enough !!!!!!!!!

I have tried emptying the pond and fitting a new liner but blow me if it
didn't come back.

Sure - some little bird had a bath in someone else's pond, got a bit of
duckweed on its feet that was washed off its feet when it had a bath in
your pond !

Thus far Duckweed 3 Me 0

Accept that it is not something you *can* get rid of and scoop it out
regularly. If you can't accept that then get rid of the pond


--
Jane Ransom in Lancaster.
I won't respond to private emails that are on topic for urg
but if you need to email me for any other reason, put ransoms
at jandg dot demon dot co dot uk where you see