Algae on a pool deck is a slip hazard, not a stain
The film that builds where the deck stays damp — shaded corners, the splash zone, under the screen line — turns slick the moment it’s wet. Kids run on pool decks barefoot; that’s the whole problem in one sentence. Cleaning it isn’t cosmetic maintenance, it’s taking the slickest surface at your house back to grippy. The difference underfoot is immediate.