See how pros apply Stain Barrier to prevent organic matter from seeping through.
What looks like a common black algae stain is actually fungus or bacteria permeating through the liner from the behind.
Pulling back the liner reveals a contaminated pool floor, possibly the result of a high water table.
Begin by scraping off and removing all debris and filling in all cracks.
Stain Barrier rolls on like paint. Pros are careful to cover the entire surface of the vessel including all seams between panels.