A pool in Tulum should hold free chlorine between 1 and 3 ppm, pH between 7.2 and 7.6, alkalinity between 80 and 120 ppm and calcium hardness between 200 and 400 ppm. The order of adjustment matters: alkalinity first, then pH, and chlorine only at the end.
| Parameter | Correct range | What happens out of range |
|---|---|---|
| Free chlorine | 1 – 3 ppm | Low: algae in 48 h. High: irritation and corrosion |
| pH | 7.2 – 7.6 | High: chlorine doesn't disinfect. Low: attacks finish and metal |
| Total alkalinity | 80 – 120 ppm | Low: pH bounces uncontrolled. High: pH won't come down and lime precipitates |
| Calcium hardness | 200 – 400 ppm | High: scale. Low: the water attacks the finish |
| Cyanuric acid | 30 – 50 ppm | Low: the sun consumes the chlorine. High: it blocks the chlorine |
| Phosphate | Under 200 ppb | High: algae that return despite chlorine |
Plenty of people adjust pH and find it has climbed again the next day. It isn't that the product doesn't work: it's that alkalinity is out of range. Alkalinity is what buffers pH. If it's low, pH bounces; if it's high, pH won't come down no matter how much acid you add. That's why the correct order is: 1) alkalinity, 2) pH, 3) calcium hardness, 4) chlorine.
The Yucatán peninsula is limestone, and water drawn from the aquifer comes loaded with calcium carbonate. That means a pool in Tulum starts out with high hardness and alkalinity, while a manual written for central Mexico assumes middling values. In practice, the constant work here is bringing values down, not up: lowering alkalinity, controlling saturation and preventing lime from precipitating.
Cyanuric acid protects chlorine from solar radiation. Without it, in Tulum you lose half your free chlorine in an afternoon. But past 50 ppm the opposite happens: it locks the chlorine and leaves it inactive even though the meter says it's there. Because cyanuric acid doesn't degrade and accumulates with every trichlor tablet, plenty of Tulum pools end up at 100 ppm or more with water that isn't disinfecting despite "having chlorine". The only way to bring it down is dilution with fresh water.
Free chlorine is the part that disinfects. Combined is chlorine already spent, bound to organic matter: those are chloramines, and they're responsible for the strong pool smell and red eyes. Total is the sum. If the smell is strong, the problem isn't excess chlorine but a shortage of free chlorine, and the fix is a shock, not a smaller dose.
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Free chlorine between 1 and 3 ppm, with pH between 7.2 and 7.6. In Tulum it's worth holding the upper end of the range because of solar radiation and water temperature, which degrade chlorine far faster than in temperate climates.
Almost always from high alkalinity or from very hard fill water, which is normal with a well in Tulum. Alkalinity buffers pH: if it's above 120 ppm, pH tends to climb and resists coming down. The fix is adjusting alkalinity first, not adding more acid.
The strong pool smell isn't chlorine: it's chloramines, chlorine already spent and bound to organic matter. It signals a shortage of free chlorine, not an excess. It's resolved with a shock chlorination that breaks those chloramines down.
The three real causes, how to tell them apart and how long the rescue takes.
Read →Dull or milky without being green: five causes and how to tell them apart.
Read →Rain, nortes, sargassum and high season: what to adjust in each period.
Read →If your pool isn't crystal clear when we finish, that visit is on us. No fine print.
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