Free chlorine (3–5 ppm in summer)
The sanitizer. Below 1 ppm algae and bacteria grow; above 10 ppm the water is uncomfortable. Summer sun and swimmers burn it off, so summer targets are higher than the strip-bottle numbers.
pH (7.4–7.6)
Chlorine is weak above 7.8 and the water becomes corrosive below 7.2. Salt pools and new plaster push pH up; rain and heavy chlorination push it down.
Total alkalinity (80–120 ppm)
The buffer that stops pH from swinging. Low alkalinity means pH bounces around; high alkalinity locks pH high and causes scale.
Cyanuric acid (30–50 ppm)
Stabilizer. Shields chlorine from UV. Too low and chlorine disappears by noon; too high (over 90) and chlorine stops working even though the test shows plenty. Houston tap water adds none, tablets add a lot.
Calcium hardness (200–400 ppm)
Low calcium etches plaster; high calcium scales tile and heaters. Houston water is moderately hard, so this mostly matters after refills.
Salt and phosphates
Salt 2,700–3,400 ppm for salt pools. Phosphates under 500 ppb; they arrive with fertilizer runoff and feed algae.
Questions
Why do the readings change week to week?
Weather. A storm dilutes everything, a heat wave burns chlorine, a pool party consumes it. The weekly visit corrects the drift before it becomes a problem.
Can I test at home?
Yes, strips are fine for a quick check. Your technician uses a liquid or photometer kit for the report.