On Mon, 27 Feb 2017 13:47:51 +0000, Janet wrote:

I wouldn't use bleach. When our concrete back steps get slippery with
algae I use Jeyes fluid, elbow greas, a scrubbing brush, and rince with
hose.


you might try the very useful paving website belonging to
professional paver and ex-urgler Tony

http://www.pavingexpert.com/maintain_02.htm


But this does recommend the use of bleach!

Ermin