pH, alkalinity, and chlorine: a practical pool water guide

Why these three numbers define “stable” pool water

pH, total alkalinity, and free chlorine work as a system. When one drifts out of range, the others often follow.

In Costa Rica, pools run year-round with heavy rain, constant humidity, strong sun, and organic load (leaves, dust, sediment). That’s why guessing usually turns into recurring problems.

What each parameter really means

pH
pH affects comfort and chlorine performance. Out-of-range pH can reduce sanitation, cause irritation/corrosion, and contribute to scaling or cloudy water.

Total alkalinity
Alkalinity buffers pH. Too low → pH swings. Too high → pH keeps rising and is hard to control.

Free chlorine
This is the active sanitizer. When chlorine won’t hold, you typically see cloudiness, algae, and strong odors (often linked to high bather/organic load).

Practical reference ranges

As general operating references:

• pH: 7.2 – 7.8
• Total alkalinity: 60 – 200 ppm
• Cyanuric acid (if used): 20 – 50 ppm
• Minimum free chlorine: depends on temperature and whether cyanuric acid is used (warmer water needs higher minimums)

What to test first (the order that saves money)

1) Free chlorine
If sanitation is failing, everything else becomes harder.

2) pH
Because it strongly affects performance and comfort.

3) Total alkalinity
To stabilize pH and reduce daily corrections.

4) Cyanuric acid (if applicable)
If it’s out of range, chlorine can be difficult to maintain.

Common scenarios and what they usually mean

pH keeps rising
Often driven by high alkalinity, aeration (waterfalls/jets/overflows), and frequent top-ups.

Chlorine won’t hold and algae appears
Common causes include strong sun, high organic load (rain/vegetation), under-filtration, or cyanuric acid issues.

Cloudy water + “strong chlorine smell”
That smell doesn’t guarantee effective sanitation. It often points to high contamination load or poor filtration/balance.

Scaling / mineral buildup
Often linked to persistently high pH and overall water balance, especially with evaporation and refills.

Rainy season: don’t ignore dilution and runoff

Heavy rains dilute chemicals, increase organic debris, and load the filter. Best practice is consistent testing, adjusting filtration time as needed, and avoiding panic dosing without testing.

Mistakes that make maintenance expensive

• Adjusting pH, alkalinity, and chlorine all at once without letting water stabilize
• Buying chemicals based on generic advice instead of measurements
• No log/history (everything becomes trial and error)
• Under-sizing equipment and trying to compensate with more chemicals

Final recommendation

When pH and alkalinity keep the water stable, chlorine performs better—and your pool becomes easier and cheaper to run in Costa Rica’s tropical conditions.