The Brew Cabin

I have laid a patio for a good customer. Since last year the some of the Bradstone slabs and many of the pointed joints have turned green. It is not moss but may be a type of fungus. There are deciduous trees nearby but not directly over the paving. There are also two dogs who use the patio regularly.:(
Any ideas as to what may have caused the greening, and how can it be controlled?

It's probably algae or possibly a lichen. Swilling down the area with Jeyes Fluid or a good weedkiller should get rid of it.

Jeyes Fluid is good for those paved areas frequented by dogs, as it disinfects their waste products, but is less effective at controlling weed growth, so, it may be a case of using a good weedkiller once every six weeks, and the JF once a fortnight for maximum protection from greening and odour.