Water Chemistry

How to Fix Green Pool Water

Green water is almost always an algae bloom, and the fix is sequential, not a single product dumped in all at once. This site is dedicated to a single build method: gunite (shotcrete) construction, rebar cage, sprayed and hand-finished concrete, engineered bond beams, and a design that can be shaped to anything the lot allows, from tanning ledges to negative edges to integrated spas.

Brick-paved pergola courtyard with fountain

Green water means algae has outgrown the sanitizer, usually after a few days of low chlorine, heavy rain diluting the water, or a filter running behind. The fix follows a set order: test, correct, shock, filter, repeat.

Test before adding anything
Check pH and alkalinity first. Shock dosed into badly out-of-range water is less effective, so correct alkalinity (80-120 ppm) and get pH into range before shocking.
Brush the pool
Brush walls, steps, and corners to knock algae off surfaces and into suspension where chlorine can reach it; algae clinging to plaster survives a chemical treatment that only touches open water.
Shock at the right dose
A standard algae-level shock is typically 2-4x the normal maintenance dose (check the product label for pool volume), applied in the evening so sunlight does not burn it off before it works.
Run the filter continuously
Run the pump and filter around the clock until the water clears, not on a normal timer schedule; dead algae has to be filtered out, and that takes continuous turnover, not periodic bursts.
Clean or backwash the filter afterward
A filter that just cleared a green pool is loaded with dead algae; backwash a sand/DE filter or hose off a cartridge filter once the water is clear so it is not immediately overloaded again.
Retest in 24-48 hours
Water that looks clear can still have algae regrowth starting if chlorine demand was underestimated; retest and re-shock lightly if the chlorine reading has dropped fast overnight.

FAQs

How long does it take to clear a green pool?

Typically 24-72 hours with continuous filtration once the shock and brushing are done correctly; a severely overgrown pool or one with a struggling pump can take longer.

Do I need an algaecide, or is shock enough?

Shock (raising free chlorine high enough to overwhelm the algae) does the heavy work; an algaecide can help prevent regrowth afterward but is not a substitute for correcting chlorine demand and brushing the surfaces.