I just tried this product after a recommendation from this group.
It requires no scrubbing or rinsing!!! It's called Spray & Forget.

http://www.sprayandforget.com/

It's a concentrated liquid that should be mixed to a 9:1 ratio for
existing black algae streaks. 5:1 for moss. You may want to order
their special made hose end sprayer because standard hose end
sprayers can't get close to mixing these ratios.

It takes a while to do its magic (6-9 months) but again requires no
damaging scrubbing or rinsing!!! It should be applied every 18-24
months thereafter as a preventative.