Greenish tinge on block paving

Chlorine granules as used for hot tubs (about 1000x the mixture you should put in a hot tub) will work - don't ask me how I know this.

More likely algae than moss IMHO. I'd go for diluted bleach, scrubbed in with a yard brush, then rinsed.

The best stuff I've found is Armillatox. It used to be sold as something like moss and algae killer, but due to some EU regulation it's now sold as "soap based cleaner" or something similar. I think it's coal tar based.

I've also used iron (II) sulphate to kill moss, but that will stain concrete orange.

There's no permanent solution. Even the temporary ones are very temporary. I just pressure jet my driveway every spring. Clears the weeds away for a while too.

In message , harry writes

Agreed. Our neighbour has horse chestnut (conker) trees along the wall between our properties, with my drive running below the canopy. I've tried pressure washing, bleach, Jeyes, Dettol and others, all of which work to an extent, but only offer a temporary solution.

I really don't want to get into the routine of pressure washing. I am convinced it makes the blocks more susceptable to further problems due to it washing off some of the surgace agregate.

well, thats your choice, but it works as does acid and bleach. Both kill some sorts of algae/lichens