You uncover the pool and the water has gone green. Algae is one of the most persistent problems you will run into, but it is preventable, and once it shows up you can clear it with the right approach. Here is why it develops, how to keep it out, and what to do when it takes over.
Algae spores are always in the air around your pool, and they take hold fast when sanitizer or circulation slips. Algae needs three things to grow:
There are three main types of pool algae, each requiring a different approach. Identify which one you have, then follow its treatment.
Green, cloudy water with slimy walls and floors. Usually from low chlorine and poor filtration.
Most common · easiest to treat
Yellow or brownish dust, often on shady walls. More resistant to chlorine and prone to returning.
Harder to kill
Dark black or blue-green spots rooted deep in the plaster. Highly chlorine-resistant.
Most stubborn · hardest to remove
Algae prevention is much easier than dealing with a full-blown outbreak. Here are key habits to incorporate into your routine.
Algae loves to cling to pool walls and floors. Regular brushing prevents it from gaining a foothold.
Algae is common, but it does not have to keep coming back. A pool with steady chlorine, good circulation, and regular cleaning rarely blooms. If one does take hold, move fast: shock, scrub, and filter aggressively until the water clears.
Shock the pool to raise chlorine sharply, brush the walls and floor to loosen the algae so sanitizer can reach it, then run the pump continuously and clean the filter afterward. Move fast and keep filtering aggressively until the water clears.
Algae takes hold when chlorine slips, circulation goes stagnant, or nutrients like phosphates and organic debris build up. Keep chlorine at 1-3 ppm, run the pump 8-12 hours a day, and brush weekly, and a pool rarely blooms.
It is best not to. Algae itself signals that sanitizer is too low to keep the water safe, and the same conditions let bacteria thrive. Clear the bloom and restore chlorine before swimming.
Black algae is the most stubborn. It roots deep into plaster behind a protective layer, so you have to scrub with a stiff brush to break that layer, apply chlorine directly to the spots, shock the pool, and run the pump continuously for at least 24 hours.
