Getting rid of the black spots

[ColinM50]

Our patio has been down about twelve years, Marshalls Indian sandstone, and it was getting quite grubby. So paid a local chappie to powerwash it and it's come up really quite well and I'm happy with the overall job. But there's quite a lot of black spots. Chappie used some stuff before starting the jet washing, don't know what it was but it smelled a bit like bleach. He brushed it all over and left it for an hour before starting washing.
So what can I use to get rid of the spots? It would be nice to get it all clean and pristine

[mikees]

Sodium hypochlorite or dairy bleach. 35quid for 25 litres from a swimming pool shop or agri wholesaler

[ColinM50]

Sounds like the stuff he used. He did tell me what it was but I'd forgotten. But if he's already tried that and it's not quite worked, what's better?

But thanks

[langtounlad]

Benzalkonium Chloride Concentrated (BAC 50) – ideal for roof cleaning, soft washing, patios, decking, driveways & outdoor surfaces with lasting results. You may well find that the bleach has done the job and that the black spots will fade and disappear in the next couple of weeks. Same with the BAC 50 - results aren't instant but are long lasting.

[Nigel_O]

No connection or endorsement, but this is what a quick search came up with

https://patioblackspotremoval.com/blogs/news/what-...

[UTH]

You'll want this: https://patioblackspotremoval.com/products/patio-b...