A very underrated product for removing algae, not too strong on a hood but as a stronger solution will remove algae from paving around the house etc, unlike pressure washing it does not blast the grout out. Simply make sure the paving is damp and apply with a watering can. Before my hip became limited in its articulation I could do a piece 18 meters by 13 metres in two minutes. These days I dilute it more but travel more slowly.Diluted bleach works very well to remove algae.