If you see black spots growing in your pool, it is a sign of the beginning of black algae and you will want to treat it immediately. The longer you let it go, the harder it will be to eliminate it. Black algae generally penetrate porous pool surfaces like concrete and gunite. Once these surfaces are infested with black algae, it will take time and persistence to eliminate it. Black algae are generally not an issue with smooth-surfaced pools like fiberglass and vinyl. This guide provides a step-by-step procedure for eliminating black algae.