How to Clear a Green Pool in North Carolina (Step-by-Step)

How long does it take to clear a green pool?

Light green water clears in 24–48 hours, medium green in 3–4 days, and a dark green or black-swamp pool in 5–7 days. Filtration capacity, not chlorine, is usually what sets the timeline.

What chemicals clear a green pool fastest?

Liquid chlorine plus circulation clears algae fastest. A 15,000-gallon pool needs roughly 3–5 gallons of 10% liquid chlorine to hit 10–20 ppm, plus muriatic acid to hold pH at 7.2 so the chlorine stays effective.

• Liquid chlorine (10–12.5%): the workhorse; no CYA or calcium added.
• Muriatic acid: drops pH to 7.2 before shocking so chlorine works at full strength.
• Flocculant or clarifier: optional, only after algae is dead and water is grey-blue.
• Phosphate remover: use if phosphates exceed 500 ppb, otherwise algae returns in weeks.
• Skip powdered shock if CYA is already above 50 ppm — most cal-hypo and dichlor products add stabilizer or calcium you do not want.

Why does my pool turn green again after shocking?

Regrowth almost always means one of three things: cyanuric acid is above 80 ppm so chlorine is stalled, phosphates are feeding the algae, or the filter was never cleaned after recovery and is reseeding the pool.

The chlorine-to-CYA relationship is the piece most homeowners miss. At 100 ppm CYA you need roughly 8 ppm free chlorine just to match the sanitizing power that 3 ppm gives you at 40 ppm CYA. If your stabilizer is that high, dilution beats dosing.

When should you drain a green pool instead of treating it?

Drain when cyanuric acid exceeds 100 ppm, calcium hardness exceeds 600 ppm, or the pool is a black swamp with organic sludge. In those cases a drain plus acid wash at $700–$1,400 is faster and cheaper than weeks of chemicals.

Draining a North Carolina pool carries real risk: high water tables can pop a shell out of the ground. Never fully drain without checking the hydrostatic relief valve, and never leave plaster dry in summer sun.