First, I have a bad string algae problem that I'm been working to resolve. Not sure if it is related but thought I'd mention it. This problem has been dogging me for about 3 years. The issue that has me stumped is whenever I clean the algae by hand I'll see these white "particles" coming up from the liner surface. About the size of small pieces of sand. They are sort of grainy but I have no clue where they come from. Again, this has been around for a while. Any ideas?