Safe, family-friendly pool water comes down to five numbers in their proper ranges: free chlorine (1–3 ppm), pH (7.4–7.6), total alkalinity (80–120 ppm), calcium hardness (200–400 ppm), and cyanuric acid (30–50 ppm). When all five are in band, the water sanitizes properly, feels good on skin, and does not damage plaster or equipment.
Free chlorine — the sanitizer
Free chlorine is what kills bacteria, viruses, and algae. Target 1–3 ppm for residential pools. Too low and the pool stops sanitizing; too high and swimmers get irritated eyes and faded swimsuits.
pH — the comfort and protection dial
pH controls how comfortable the water feels and how aggressive it is on plaster and equipment. Target 7.4–7.6. Below 7.2, water etches plaster and corrodes metal. Above 7.8, chlorine effectiveness drops sharply and scaling starts.
Total alkalinity — the pH buffer
Total alkalinity (80–120 ppm) is the buffer that keeps pH stable. If alkalinity is right, pH stays put. If alkalinity is off, pH bounces and chases you every week.
Calcium hardness and cyanuric acid
Calcium hardness (200–400 ppm) protects plaster from etching at the low end and from scaling at the high end. Cyanuric acid (30–50 ppm) is sunscreen for chlorine — without it, UV burns chlorine off in hours.
Why families should care
Balanced water means swim-safe water. It also means a pool you can confidently invite friends and family into without worrying about red eyes, ear infections, or the slick algae step. This is exactly why we treat chemistry as the most important part of every weekly visit.