How long does it take to clear a green pool?

Usually 1–2 days of holding shock level with the filter running around the clock. A deep, dark-green pool can take longer and several rounds of shock; a faint tinge often clears overnight.

Should I lower pH before or after shocking?

Before. Chlorine works best at pH 7.2–7.6, so balance pH first — shocking at high pH means a big chunk of the chlorine you add is wasted.

My pool is still cloudy after shocking — is that normal?

Yes. Once algae is killed it turns from green to cloudy white, and the filter clears that over the next several hours to a day. Keep filtering; don't stop early.

How do I stop it going green again?

Keep free chlorine at 1–3 ppm and test every 2–3 days — sooner in heat, after parties, or after heavy rain. Consistent low-level chlorine prevents the bloom that a lapse invites.

Green water

Why your pool turned green — and how to clear it

Green water is algae, and algae only blooms when free chlorine has dropped too low to hold it back. The good news: it's almost always fixable at home in a day or two without draining a drop.

Why it happened

Chlorine gets used up — by sun, heat, heavy swimming, or rain — and once free chlorine falls below ~1 ppm, algae spores that are always in the water start multiplying. A hot spell or a few missed test days is usually all it takes. It's a symptom of low chlorine, so the fix is about getting chlorine high enough, for long enough, to kill it.

The fix, step by step

1. Balance pH first (7.2–7.6). Chlorine is far more effective in this range — shocking at high pH wastes half of it.
2. Shock hard (10–15 ppm).Raise free chlorine to shock level with the filter running. Do it at dusk so the sun doesn't burn it off before it works.
3. Brush and filter.Brush the walls and floor to break up algae, and run the filter continuously — it's what physically removes the dead algae.
4. Hold and repeat. Re-test and re-dose to keep it at shock level until the water goes cloudy-white, then clear — often a day or two.
5. Re-test before swimming. Only get back in once free chlorine has settled to 3 ppm or below and pH is in range.

Work out your exact dose

Numbers in hand? This free calculator turns them into the exact amount for your pool's size:

Pool Shock CalculatorHow much shock to add to reach shock level and clear the water.

Frequently asked

How long does it take to clear a green pool?: Usually 1–2 days of holding shock level with the filter running around the clock. A deep, dark-green pool can take longer and several rounds of shock; a faint tinge often clears overnight.
Should I lower pH before or after shocking?: Before. Chlorine works best at pH 7.2–7.6, so balance pH first — shocking at high pH means a big chunk of the chlorine you add is wasted.
My pool is still cloudy after shocking — is that normal?: Yes. Once algae is killed it turns from green to cloudy white, and the filter clears that over the next several hours to a day. Keep filtering; don't stop early.
How do I stop it going green again?: Keep free chlorine at 1–3 ppm and test every 2–3 days — sooner in heat, after parties, or after heavy rain. Consistent low-level chlorine prevents the bloom that a lapse invites.

More pool help

Common pool problems — Green, cloudy, low chlorine, drifting pH — what's wrong and how to fix it.
How much chlorine to add — Hit a safe 1–3 ppm — the rule of thumb, worked examples, and why it won't hold.
How to lower your pool's pH — Pool pH too high? Why it matters and how to bring it back to 7.2–7.6.
How to raise your pool's pH — Pool pH too low? Acidic water stings and corrodes — how to bring it back up.
Cloudy pool water — Clear but not green? The three usual causes and how to get back to clear.
Chlorine won't hold — Chlorine crashing to zero is a demand to shock out — how to diagnose and fix it.
How much shock to add — Reach shock level (10–15 ppm) to clear the water — what it means and how much.

Stop guessing, start swimming

Algae Later reads your pH and chlorine, tells you exactly what to add, and nudges you when it's time to test again.

Set up your pool — free