I've been using sodium hypochlorite 12% recently with great results. It is a strong chem though, so gloves & goggles are essential, and it will damage plants if not rinsed off quickly. I've had a couple of jobs where it was as simple as "Spray on, wait 10 minutes and rinse",.. no scrubbing at all hardly. I dilute it 2 parts water to 1 part chem and add some fairy liquid as the foam stops it running off the roof so fast.