I recently posted about how to clean a lot of fencing panels prior to re-staining.
I had tried Sodium Hypochlorite & Lauryl Dimethylamine Oxide mix, this worked very well on my sandstone patio, but concerned about bleaching effect on the wood, removal of colour from existing stain, and how this could effect longevity of new stain.
Did a lot of Googling around and came across a product recommendation ... 'Wet & Forget'
I managed to get a sample to try ..... diluted 5 to 1 ... simply sprayed it on ... no agitation whatsoever. All algae dead the next day ..where it was thin ... simply gone, where it was thick, what remains is a white powder.
This can be brushed off or it will wash off in the rain.
Impressed how well this performed. It contains no bleach and has unlimited shelf life ... as it also works on brick & stone I just ordered 20L of it ... and will spray my cills, lintols, pillars & copings. As well as all fence (6000 sq ft) and the patio to stop re-growth.
It seems it is well advertised on the TV shopping channels - I went to manufacturers web site .. and their price was the same .......... but importantly there is also a 20% scheme if you get recommended by a user. Discount applies to both party's.
(happy to recommend any of you if you want the 20% off - ping me an email)
I used that and saved a nice chunk of money.