So the pool company arrived and removed my old liner in prep for the new one... What a mess it is underneath! Algae all over and holes in the vermiculite. Any idea what causes this?? I thought algae needed sunlight to grow? The liner did have a seperation in it right about at the water line, so I know water has been getting under the liner there, but there is algae even growing on the slope where the water would've run down instead of sitting. Could this be from groundwater seeping up through?? The installer told me it is neccessary to get all the algae removed before the new liner goes in, otherwise it will take the print off the liner even though it is on the backside. This is VERY evident in the old liner; The print is gone off the old liner anywhere that there was algae underneath it. Is there any way to prevent this from happening if its groundwater seeping in causing the algae??