On Fri, 06 Nov 2020 22:27:09 +0000, Chris Hogg wrote:
On Fri, 6 Nov 2020 20:59:05 +0000, F news@nowhere wrote:


We've got a patio made up of light coloured concrete paving slabs
with a
slightly rough texture. I've used a Karcher power washer to remove
the
compost that the resident gardener has managed to tread into them
but
there's a green stain (algae?) that's pretty resistant to removal.

Anyone got any suggestions on what might shift it?


'Patio Magic' aka Benzalkonium chloride. It contains the same stuff
as
Alan recommended, but with a more pronounceable name, and is more
dilute! Take your pick from e-bay suppliers here
https://tinyurl.com/y56baf45


+1; good stuff. Wilko and Robert Dyas sell it for something like £8.