Customer has this at the back of a house and it's pretty dirty.
I've told them that pressure washing will probably be safest but they seem keep to use chemicals to kill off the algae (they mentioned Patio Magic and I told them to call the customer helpline before letting it anywhere near the decking). Anyone more knowledgeable than I am able to tell me what might be suitable? To be clear, I'm not going to do this; I just don't want them to wreck the deck.
Vin