Without regular maintenance, your pool water will allow the rapid growth of algae. Algae growth that sits in your pool for months or more at a time will stain the porous plaster of the pool so deeply that you won’t be able to remove it with regular scrubbing. Another sign that your pool needs an acid-wash is the quick growth of algae after scrubbing it. Algae spores can burrow deep inside the porous plaster and continue to bloom, which the acid-wash should completely eliminate.