Why Water Chemistry Is Non-Negotiable
Clear, inviting pool water doesn't happen by accident — it's the result of carefully balanced chemistry. Get it right, and your water is safe, comfortable, and easy to maintain. Get it wrong, and you'll face cloudy water, skin irritation, algae outbreaks, and accelerated corrosion of your pool equipment and surfaces.
The good news is that pool chemistry, while it sounds intimidating, comes down to monitoring and adjusting a handful of key parameters.
The Core Parameters You Need to Know
1. Free Chlorine (FC)
Chlorine is your primary sanitizer — it kills bacteria, viruses, and algae. Target range: 1.0–3.0 ppm (parts per million). Too low and your pool becomes a breeding ground for pathogens. Too high and it irritates eyes and skin.
Tip: Chlorine degrades rapidly in sunlight. Using a stabilizer (cyanuric acid) protects it from UV breakdown.
2. pH
pH measures how acidic or alkaline your water is on a scale of 0–14. Target range: 7.2–7.6. This is the most important parameter to keep in range because it affects every other chemical's effectiveness.
- Low pH (acidic): Corrodes metal fittings, etches plaster, irritates eyes and skin, and rapidly destroys chlorine
- High pH (alkaline): Reduces chlorine effectiveness, causes cloudy water and scale deposits
Use sodium carbonate (soda ash) to raise pH, and muriatic acid or sodium bisulfate to lower it.
3. Total Alkalinity (TA)
Alkalinity acts as a buffer for pH, preventing it from swinging wildly. Target range: 80–120 ppm. When alkalinity is too low, pH becomes unstable and hard to control. When it's too high, pH tends to drift upward and water can turn cloudy.
Raise TA with sodium bicarbonate (baking soda). Lower it by adding muriatic acid with the pump running.
4. Cyanuric Acid (CYA) — Stabilizer
CYA protects chlorine from UV degradation, dramatically extending its effective lifespan in outdoor pools. Target range: 30–50 ppm. If CYA climbs too high (above 80–100 ppm), it actually begins to suppress chlorine's sanitizing power — a condition sometimes called "chlorine lock."
The only way to lower excessive CYA is to partially drain and refill the pool.
5. Calcium Hardness (CH)
This measures the concentration of dissolved calcium in the water. Target range: 200–400 ppm.
- Too low: Water becomes "hungry" for calcium and will leach it from plaster, grout, and concrete surfaces
- Too high: Causes white scale deposits on surfaces and inside equipment
The Langelier Saturation Index (LSI)
For those who want a more precise picture of water balance, the LSI is a formula that combines pH, temperature, alkalinity, and calcium hardness into a single score. An LSI near 0 means balanced water. A negative score means corrosive water; a positive score means scale-forming water. Many pool supply stores and apps can calculate it for you.
Testing Your Water: How and How Often
Test your pool water at least once a week during swim season. You have three main options:
- Test strips: Quick and easy, though less precise. Good for routine checks.
- Drop-based test kits: More accurate. The DPD method for chlorine and phenol red for pH are industry standards.
- Professional water testing: Many pool supply stores offer free or low-cost computerized analysis. Recommended monthly for a comprehensive reading.
The Golden Rule: One Change at a Time
When adjusting water chemistry, change only one parameter at a time and retest after several hours before making another adjustment. Multiple simultaneous changes make it impossible to know what worked — and can cause dangerous reactions when chemicals interact.
Summary: Quick Reference Table
| Parameter | Target Range | Raise With | Lower With |
|---|---|---|---|
| Free Chlorine | 1.0–3.0 ppm | Chlorine products | Dilution / time |
| pH | 7.2–7.6 | Soda ash | Muriatic acid |
| Total Alkalinity | 80–120 ppm | Sodium bicarbonate | Muriatic acid |
| Cyanuric Acid | 30–50 ppm | Stabilizer/conditioner | Partial drain/refill |
| Calcium Hardness | 200–400 ppm | Calcium chloride | Partial drain/refill |