Hotel pool water care: measuring and correcting pH and chlorine each day

Measure free chlorine and pH at the pool at least three times a day, first before anyone swims and then every four hours. Correct pH before chlorine, because chlorine loses killing power as pH rises. Hold pH at 6.5 to 7.8 and free chlorine at 1 to 3 mg/L outdoors, 1 to 1.5 mg/L indoors, and record every reading.

For example, a morning reading shows free chlorine 1.4 mg/L and pH 8.1. One number sits inside the legal range, the other does not, and the order in which you fix them decides whether the pool opens on time and whether the chlorine you add does anything at all. Hotel swimming pool maintenance lives or dies on this pair of numbers, read together, at the pool, three times a day.

This article explains what pH and free chlorine actually measure, what the regulation requires, how to take a reading that can be trusted, in which order to correct, how to check an automatic dosing system, and what belongs in the log and on the notice board.

What do pH and free chlorine do in pool water?#

pH measures how acidic or alkaline the water is, on a scale with no unit. Free chlorine is the chlorine still available to kill germs. They are read as a pair because pH decides how well that chlorine works.

Each whole step on the pH scale is a tenfold change in acidity, so 8.0 is ten times less acidic than 7.0. A reading that moves from 7.4 to 7.9 is a large move, not a rounding error. This is why pH is logged to one decimal and treated as a live number, not a background one.

Free chlorine is chlorine that has not yet reacted with anything. Bound chlorine, also called combined chlorine, has already reacted with sweat, urine, sunscreen and other organic matter, and in that form it disinfects poorly. Total chlorine minus free chlorine gives bound chlorine, which is why a pool can smell strongly of chlorine while free chlorine reads normally: the smell comes from the bound fraction, not from too much free chlorine.

As pH rises, a larger share of the free chlorine sits in a slow-acting form. The mg/L figure on the test kit stays the same while the water is less protected, which is why the two numbers are read together. The practical consequence follows in the correction section: never act on a free chlorine figure without the pH taken at the same moment.

Both directions of pH error cost money, in different places. Low pH irritates eyes and corrodes metal fittings, grout and heat exchangers over time. High pH scales surfaces, clouds the water and reduces the chlorine's effect.

Cyanuric acid, the stabiliser in some chlorine products, shields chlorine from sunlight but holds it more tightly as it accumulates. Annex 1 caps it at 100 mg/L for that reason.

What are the legal limits, and how often must you test?#

In Türkiye the limits and the testing frequency come from the annexes of the pool health regulation, not from the product label or the dosing pump's default setting. The operator tests three times a day; the provincial health directorate tests monthly.

The source is the Regulation on the Health Principles for Swimming Pools, published in the Resmî Gazete on 6 March 2011 (No. 27866), whose annexes were amended on 15 December 2011 (No. 28143). Quote values only from the consolidated text on mevzuat.gov.tr, never from a supplier's page. Annex 4 sets the operator's own schedule: temperature, pH and free chlorine at least three times a day, the first before the pool is used and then every four hours; colour, turbidity and cyanuric acid daily; total alkalinity weekly.

Free chlorine, hydrogen peroxide and biguanide are measured at the pool itself, not on a sample carried to an office. Where ozone, UV, chlorine dioxide or another system does the disinfecting, the free chlorine band is much narrower, 0.3 to 0.6 mg/L, and the operator's routine changes with it. Pools using hydrogen peroxide with biguanide are measured on a different scale entirely, shown in the table below.

The directorate's monthly chemical, physical and microbiological checks do not replace the operator's readings. They catch a problem after it has lasted weeks; the three-a-day reading catches it after four hours. The full set of duties around staff, sampling and records is laid out as a checklist in our guide to the pool health regulation as a checklist for water, staff and records.

Values are from the regulation's annexes as amended 15 December 2011; confirm against the consolidated text before printing anything on a board.

How do you take a sample and read it correctly?#

Take the water below the surface, away from the inlet and the skimmer, rinse the test cell with the sample twice, and read it at the pool within the time the device states.

Sample at elbow depth, an arm's length from the wall, away from a return inlet, a skimmer throat and the spot where the last dose went in. Those places carry either fresher or older water than the pool body. Rinse the cell or cuvette twice with the water you are about to test, then fill it: residual rinse water from the tap or from the previous sample shifts a chlorine reading.

Use one method consistently. Strips, a colour comparator and a photometer read differently from each other, and the trend across the day matters more than the gap between two devices, so choose one and keep it. Read at the wait time the device states, no earlier and no later: a photometer read too early or left standing drifts, and the drift is largest exactly where it matters, at the edges of the band.

If you use a photometer, zero it with the same pool water, wipe the cuvette dry on the outside, and hold it by the cap. Fingerprints and droplets read as turbidity. Write the reading down at the pool, with the time, the water temperature and the name of the person who took it; a reading remembered and logged an hour later is not a record.

Why is pH corrected before chlorine?#

Because pH decides how much of the free chlorine already in the water is actually working. Correcting chlorine first usually means correcting it a second time an hour later.

At high pH a larger share of free chlorine is in a slow-acting form. The reading can sit inside the 1 to 3 mg/L band while the water is under-protected, so adding more chlorine raises a number without raising the protection. pH correctors and chlorine products also move the other parameter: many chlorine products shift pH as they dissolve, so a chlorine dose given first can undo a pH correction, and the log then shows two corrections where one was needed.

The working order is: read both, correct pH, run circulation for the time the label states, re-test, then correct chlorine if it is still out. If pH will not hold after correction, look at total alkalinity before adding more pH corrector; alkalinity is the buffer that keeps pH steady, tested weekly under Annex 4 with a band of 30 to 180 mg/L.

Change one thing at a time. Two products added together, with circulation running, leave you unable to say which one moved the reading and by how much. Record the reading before and after each correction: the pattern over a week tells you whether the pool has a dosing problem or a buffering problem.

How do you raise or lower pH and chlorine?#

With the product the label names, at the dose the label calculates for your pool volume, added with circulation running, then re-tested before anything else goes in. This article gives no doses; the label and the pool volume do.

No universal dose exists. The amount depends on the product's concentration, the pool volume and how far the reading has to move. Take the figure from the label and write the calculation in the log so the next operator can follow it.

Know the pool volume in cubic metres before anything else. For a rectangular pool it is length times width times average depth; irregular pools need the figure from the project drawings. Without it, no dose can be calculated at all. Add the product to water, never water to the product, and follow the label on pre-dissolving, pouring point and protective equipment; labels differ between brands and between granular, liquid and tablet forms.

Keep circulation running for the time the label states before re-testing. A reading taken ten minutes after dosing measures the dose, not the pool. Stabilised chlorine products add cyanuric acid, which accumulates and is only reduced by dilution; Annex 1 caps it at 100 mg/L, so a pool on stabilised tablets all season will eventually need water replacement, not more tablets.

Never mix products, and never add a chlorine product and a pH reducer at the same place at the same time. Follow the label's interval between them. Record product name, amount, time, and the reading before and after; if the water later turns cloudy or green, that record is what tells you whether the cause is chemistry, filtration or bather load. The diagnosis itself is covered in our guide to cloudy or green pool water: finding the cause and the order of correction.

How do you check an automatic dosing system, and what changes on a busy day?#

Check the pump against a hand reading every day, and expect the setpoint to fall behind exactly when the pool is busiest, because the controller responds to the water it has already seen, not to the number of people in it.

Daily checks on the dosing pump#

Compare the controller's displayed value with a hand test taken at the pool at the same moment. A probe that has drifted reads confidently and wrongly, and the pump then doses to a false number. Calibrate the probe on the interval the manufacturer states, with fresh calibration solution, and write the date in the log; an uncalibrated probe is worse than no probe, because it is trusted.

Check the dosing lines for air, crystallised product at the injection point and an empty drum. A pump running against an empty drum reports normal while dosing nothing. Confirm the injection point sits after the filter and before the pool, and that circulation is actually running when the pump doses: dosing into still water puts a concentrated cloud against one wall.

Busy days, hot weather and rain#

Bather load consumes chlorine directly. On a full day, free chlorine falls faster than the controller's setpoint assumes, so readings between the scheduled three may be needed, and the log should show why. Hot, bright weather breaks down free chlorine faster, and stabilised products release it more slowly as cyanuric acid builds. Rain dilutes the water, drops alkalinity and carries in organic matter, so the day after rain is a pH and alkalinity day as much as a chlorine day.

A rising bound chlorine figure with a normal free chlorine reading means the pool needs oxidation and fresh water, not another automatic dose; Annex 1 caps bound chlorine at 0.2 mg/L. The filter is part of the chemistry too: run hours and backwashing decide how much the water is actually turned over, covered in our guide to hotel pool filters: backwashing, sand changes and run hours.

What goes in the analysis log and on the notice board?#

Every operator reading with its time and initials, every correction with its product and amount, and on the board the latest temperature, pH, free chlorine and microbiological results, where pool users can see them.

The log carries the three-a-day temperature, pH and free chlorine readings, the daily colour, turbidity and cyanuric acid checks, and the weekly total alkalinity figure, each with time and the person who took it. Corrections belong in the same book: what was added, how much, at what time, and the reading before and after. A log of readings alone cannot show an inspector or a manager whether the pool was corrected or simply re-measured.

Laboratory reports are kept for one year to show inspectors; keep them with the log rather than in a separate folder nobody opens. The board shows the latest temperature, pH, free chlorine and microbiological results in a place users can see. It is a display duty, not a marketing panel, so post the figures as they are.

Enforcement follows from the record. A failed chemical result brings a written warning, and closure if the repeat sample also fails; a failed microbiological result closes the pool until a new sample passes. The log is the evidence in both cases. It also feeds maintenance: a probe that drifts weekly, a pump that needs priming every morning or a filter that backwashes more often than before are all visible in the record before they become a closure. Wider scheduling of such checks belongs in a hotel preventive maintenance plan.

What to do next#

Write the pool's volume, the Annex 1 bands and the three daily test times onto one card, keep it at the pool, and run the readings and corrections in the log for a week before changing anything else. The order is the method: measure at the pool, correct pH, re-test, then chlorine, and write down what you did. The regulation sets the bands and the frequency; the log is what proves you held them.