Just cleaned the underside of my pergola which was covered with black algae. Spent 10 minutes doing one strip with a high pressure clean only 46 strips to go. Then I found this 30 second cleaning from Bunnings 30 Seconds 5L Outdoor Cleaner Concentrate This stuff works like magic !! I sprayed it on with a pressure pack and the algae literally disappeared within 30 seconds. Highly recommend !! This photo is of the strip I pressure cleaned, I'll attach another one soon of the 30second cleaner section.