Common pool problems
Green, cloudy, chlorine that won't hold, pH that keeps drifting — here's what causes each one and exactly how to fix it. Nearly every problem comes back to two numbers: pH and chlorine.
pH
7.2–7.6
aim for 7.4
Free chlorine
1–3 ppm
aim for 2 ppm
Shock to
10–15 ppm
then wait to swim
My pool has turned green
Why: Algae has taken hold — which means your free chlorine dropped too low to keep it in check.
Cloudy even though chlorine looks okay
Why: Chlorine is busy fighting something (early algae or organics), or pH has drifted high so it can't work.
Chlorine reads zero or won't hold
Why: Sun, heat, heavy use, or a chlorine demand from algae and organics can burn through it fast.
My pH keeps climbing
Why: New plaster, aeration from jets and fountains, and some chlorine types all nudge pH up over time.
The water stings my eyes and skin
Why: Usually the opposite of what people assume — either low, acidic pH or chloramines (spent chlorine), not too much chlorine.
Strong chlorine smell — add less?
Why: That sharp smell is chloramines — they form when there isn't enough free chlorine to finish the job.
How often should I test?
Why: Balance drifts constantly — and faster after parties, heavy swimming, heat waves or heavy rain.
Is it safe to swim right now?
Why: Water's only swim-ready when both numbers are in range — guessing risks sore eyes or unprotected water.
Work out the exact dose
Once you know what's wrong, these free calculators tell you how much to add for your pool's size:
Stop diagnosing, start fixing
Algae Later reads your pH and chlorine, spots the problem, and tells you exactly what to add — then nudges you when it's time to test again.
Set up your pool — free