Posted: 15/05/2017 at 17:48
There was a company at the Malvern Show by the name of 'The Patio Black Spot Removal Company'. At a guess they may be what you are looking for. Who needs Poirot when you have my deductive powers to fall back on?
Here a link to their site http://patioblackspotremoval.com/
It's not cheap, but if you've spend a lot on the patio (like me) it might be worth trying. Thankfully we don't have a problem with black spots at the moment.
Last edited: 15 May 2017 17:50:37