Water guide

Chlorine, pH and alkalinity: the right numbers for a pool in Tulum

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.

The correct ranges

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

The order of adjustment, and why it matters

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.

Why Tulum's well water changes the rules

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.

Stabilizer: the parameter almost nobody measures

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, combined and total chlorine

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.

Rather we handled it?

We provide weekly maintenance across the 25 areas of Tulum and the Riviera Maya from $1,500 MXN/month, chemicals included and crystal-clear water guaranteed. Message us on WhatsApp with a photo of your pool.

Frequently asked questions

Frequently asked.

What is the correct chlorine level for a pool in Tulum?

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.

Why does my pool's pH rise on its own?

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.

Why does it smell strongly of chlorine if I only just added a little?

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.

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