I treated ours 2 weeks ago with a patio cleaner, but this morning to shift the stains I used warm water and bleach, with a soft brush, when the sun was on it. After it had dried, stiff brush and bingo, it looks as good as the day it was laid. Lovely stones in the summer, but loves the winter algae and muck. Riven sandstone. Knackered now though, bed and my book, and get up tomorrow and make use of the weather. "She who must be obeyed" tells me that we are off out on Monday because it will be scorchio. Suits me, perhaps a tripto Treaddur bay is called for.