On 28/10/2018 15:32, Roger Tonkin wrote:
Due to me leaving a packet of ferrous sulphate out over a rainy
night, I now have a small area of my pation stained orange.

I've tried scrubbing, which helps a bit, but looking for
something easier and more positive, like: a high pressure hose
or some magic chemical.

Unfortunately any magic chemical that works will damage the paving. The
least aggressive that might shift it is a mix of mostly citric acid and
table salt about 2:1 in a paste and wash the thing clean very carefully
if the stain is weakened. It works by reducing ferric insoluble orange
back to soluble green ferrous - but oxygen in the air will take it back
in the other direction if you don't get rid of every trace.

In practice I think you are going to need a mix of citric acid and
hydrochloric acid (aka brick acid) to stand any chance of shifting it.

Whatever, it must return the slabs to the original state to
match the rest of the patio, otherwise swmbo will continue to
moan and nag

Whatever you do it will leave a mark on the part that has been cleaned.

--
Regards,
Martin Brown