I have vacuumed, put algaecide, more shock nothing makes this go away. I have drained pool and am going to scrub it down tomorrow. I am afraid this stuff will come back, does any one know what this stuff is? When I drained the pool the dirt even got white. The water was hazy then the white powder appeared when the problem started. I am afraid this stuff is in the sand filter and connecting tubs I really need help. The pool stores had no idea of what the white powder was. I really need help....