How dee do dee. Recently asked to clean wall of a spa. Large wall and it was discoloured. It was green lower down and darker higher up. Thought biocide first and then went with Bio cide. the green was taken out immediately as you would expect, but the dark remained. On closer expection it was lichen further up and the hypo has not tocuhed it. I then put some biocide on it and have left it. Anyone experiience on biocide and lichen. Am i going to have to jet wash after all? . Thinking of Patio's, Lichen will not come off without a jet wash after hypo. I had wanted to avoid jet wash as not an easy wall to get to. Any suggestions more than welcome. Thanks Jack.