I cleaned my patio at the weekend and whilst the worst of the muck is off there are still black spots of what appear to be some sort of mould. It is incredibly difficult to get off.
There is a product called Armillatox designed specifically for killing moss/algae/slime/lichen available from garden centres.
I've used it and it does a good job.
pathclear, which you dilute with water in a watering can. we use this once, maybe twice, a year and it keeps our block paved drive clear of any mould or moss. it's very easy and quick to use. our neighbour uses a high pressure hose but the mould stains are still there, and to be honest the path looks a mess because he misses areas which he can't see properly when the path is wet.
I may invest in a high pressure spray. I asked some one at work and this is what they used. They only cost about �20 - �30 (sounds very cheap to me but apparently this is what it cost) and the force of the water is quite high. It will hurt your fingers allegedly so if it will do this I would imagine it will clear the muck!
I may even try Armillatox as suggested by Woodchopper