In article , Jill Bell
writes

I've always believed that approach to work too - by the time the
oxygenators and the surface coverers have grown, the blanket weed/alga
usually gives up. Sadly this year it hasn't worked with one of our two
ponds and I'm not sure of the reason.......

You sure you didn't let a bit of fertilizer get in?

--
Jane Ransom in Lancaster.
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