Posted: 30/08/2012 at 08:46
Many thanks for that. We've now tried the following: Algae/moss killer (Patio Magic), Pathclear, Concentrated bleach, Rock salt, Mould and mildew killer with bleach, Dithane (fungicide), and Roundup. All of these were at double strength. NONE have killed it - you might like to mention that to your local guys.
Of the above, concentrated bleach was the best after covering it very thickly but it hasn't killed it. It definitely doesn't like being covered in a layer of rock salt but, again, didn't kill it. If we can't kill it, then spreading a layer of rock salt would be our best guess to try and, at least, reduce it.