I ordered 5L of Algoclear Pro. My external wall (K Rend allied by Taylor Wimpey cowboys) built in 2014 was covered in deep red and black stains, with the sporadic green algae here and there. I did not hold much hope for Algoclear Pro to completely eradicate these stains and I believed I would need to paint the wall following treatment. I used a 5L garden pump sprayer with a mix of 1:20 AP:Water and saturated the affected areas. Over the course of the next couple of hours, the red spots began to turn orange and the green algae was disappearing fast. Within 5 days, my wall looks entirely transformed. I still can't believe what a difference this has made. I have attached a photo to show the results. There is slight black marks left over so I have purchased some Metaclear to clear these up. Progreen have been fantastic. Fast delivery and answered my queries on how best to use the product. Thankyou Progreen. I will certainly order from you again.