Green or Algae Pool

Algae blooms range from a light green tint to a fully opaque swamp-green pool, and the right fix depends on how established the bloom is.

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Light Green / Early Algae

Test and rebalance pH and alkalinity first, since algaecide and shock work poorly in unbalanced water.
Brush the walls and floor vigorously to break up algae clinging to the surface before treating.
Shock the pool with a fast-dissolving chlorine shock at dusk or after dark so sunlight doesn’t burn off the chlorine before it works.
Run the filter continuously for 24 to 48 hours and vacuum any dead algae that settles to the floor.

Safety note: Wait until free chlorine drops back to a safe swimming range (roughly 1–3 ppm) before letting anyone back in the water.

Double or triple the normal shock dose, since heavy algae blooms consume chlorine almost as fast as you add it.
Add an algaecide labeled for the type of algae you have alongside the shock treatment for a stronger knockout.
Backwash or clean the filter media partway through the process, since dead algae can clog it quickly.
Retest daily and repeat shocking until the water holds a stable chlorine reading for at least 24 hours.

Safety note: Never mix chlorine shock and algaecide products in the same container, and always add chemicals to water, not water to chemicals.