On 06/11/2020 22:27, 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


Bac50 needs to be diluted 10:1 to 20:1 water:BAC50 for this application.
Possibly not that plant friendly.

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