I was a bit sceptical when I ordered this as to whether it would work. Well it certainly does – on the 1st application there was a lot of white residue but having contacted Block Blitz they assured me that was normal and that any rain would further activate the residue. After 1 application most of the algae has disappeared and looks almost new. I can’t wait for 4 weeks when I can apply the 2nd treatment. I would definatly recommend this product – so much less hassle than power washing!!