This isn't a longterm cure, but would keep the mould in check if used every 3 month or so.
A little bit goes a long way when you dilute 1 to 5. Super quick job that with a little 5 ltr spear and jackson pump sprayer.
I have a waft around with it in the winter when the garden doesn't get much sun and i can't be arsed to get the jet wash out. Do concrete fence posts and plinths.. paving, brick wall, patio and what not.
Pro-Kleen MY16 Patio Cleaner Simply Spray and Walk Away Green Mould and Algae Killer for Patios, Fencing and Decking 5 Litre Concentrate (Makes 25 litres)