How Do You Set Pool pH and Chlorine Dosage?

Every dosing calculation starts with the water volume in cubic metres, because the quantities on product labels are always given per unit of water. For a rectangular pool the maths is simple: width × length × average depth. The critical word here is "average". Most villa pools have a sloping floor; water that reaches your waist at the shallow end can be over head height at the deep end. If you use only the deep-end measurement you will overestimate the volume, and if you use only the shallow end you will underestimate it. Measuring the depth at both ends and taking the average is what makes the dosage genuinely yours.

For freeform, kidney or L-shaped pools it is enough to split the pool into a few rectangles and add the results; you are looking for a consistent reference, not absolute precision. Steps, seating ledges and, where present, the overflow channel and balance tank also change the total amount of water. That is why we recommend calculating the volume carefully once and writing it down. In our regular pool maintenance service, every pool's volume is recorded in its technical file, and all dosing calculations through the season rest on that single figure.

The order of testing is not arbitrary: alkalinity first, then pH, and chlorine last. Total alkalinity is the buffer for pH; once it falls below the 80–120 ppm range, pH swings from one day to the next and every correction you make to it is short-lived. When alkalinity sits where it should, bringing pH into the 7.2–7.6 range is both easier and longer-lasting. The reason chlorine comes last is simple: a chlorine reading taken while pH is wrong does not tell you how well the water is actually protected.

Always test under the same conditions: take the sample at elbow depth rather than from the surface, away from the skimmer and the return inlet, and rinse the vial with pool water first. If the reagents are past their expiry date, the reading will be quietly wrong, which is why the bottles should never be left in heat or sunlight. Repeating the test at the same time of day, after the filtration has run, also makes your results comparable with one another. From drop kits and test strips to photometric devices and full test sets, we cover which testing method suits you in our pool test kit comparison.

Not all the chlorine in a pool does the same job. Once chlorine enters the water it is shared between two forms depending on pH, and only one of them behaves as a strong disinfectant. As pH rises, the share of that effective form falls: your test kit may show the same free chlorine figure while the water's real disinfecting power drops. When pool owners tell us they keep adding chlorine and see no result, the problem is usually not the chlorine but a pH that has crept up.

Pool water pH naturally tends to rise; fresh top-up water, aeration and hot weather all push it that way. That is why a pH reducer is the adjuster most often needed, and liquid forms such as Quardex liquid pH reducer are practical because they blend into the water quickly. In the other direction, once pH falls below 7.2 the water becomes corrosive, eyes and skin are irritated and chlorine burns off fast. In both cases the product label tells you which product and how much; your job is to bring pH into the right range and let the chlorine work.

Cyanuric acid, commonly known as stabiliser, slows the breakdown of chlorine in sunlight. In an unprotected pool, summer sun consumes a large part of the chlorine you added in the morning within the same day; stabiliser reduces that loss considerably. The target range is 30–50 ppm. Below it your chlorine consumption is needlessly high; above it the effect reverses: chlorine remains present in the water but no longer works as quickly. Water that will not recover while the test still shows chlorine is often a sign of exactly this.

The most important property of stabiliser is that it does not decrease on its own. Unlike chlorine it is not consumed; it is only diluted by backwashing, overflow and top-up water. So if you use stabilised products through a long season, you may find the value climbing quietly. Slow-release tablets such as WTR multifunction chlorine tablets, for instance, are very practical for steady disinfection, but with continuous use you need to measure cyanuric acid as well. If you are wondering which product family answers which need, our pool chemicals guide explains that distinction product by product.

To read test results correctly you need to separate three terms. Free chlorine is chlorine that has not yet combined with any contaminant and is ready to do the disinfecting work; your 1–3 ppm target refers to this value. Combined chlorine has already bonded with organic load such as sweat, sunscreen or leaves and can no longer disinfect; it is also known as chloramine. Total chlorine is the sum of the two. The gap between total and free chlorine therefore tells you how much combined chlorine has built up in the water.

The distinction matters in practice, because combined chlorine is what creates the sharp "chlorine smell" and stinging eyes people associate with pools. In other words, in a strongly chlorine-smelling pool the problem is usually not too much chlorine but exhausted chlorine, and the answer is not less contact with chlorine but recovering the water. This normally calls for a shock treatment; high-concentration products such as Selenoid granular chlorine are used for it, again in the quantity given on the label. We look at the other root causes of odour and cloudiness separately in our article on cloudy and smelly pool water.

Pool water is not a system that responds instantly. A chemical you add needs a few hours of circulation, with the pump running, to spread through the whole volume and produce a measurable effect. That is why the rule in experienced practice is clear: add part of the dose the label recommends, let the water circulate, measure again and top up if needed. When a large correction is made in one go, the value overshoots the target, the opposite chemical is added to fix it, and the pool swings like a pendulum for the rest of the season.

The same discipline applies to how you apply the product. Granular products are never scattered straight into the pool; they are first dissolved in a clean bucket of water, then spread across the surface while the pump is running. Tablets are not dropped on the floor but used as the label indicates. Two different chemicals are never added at the same time; circulation time is left between them. Rather than emptying the product at a single spot, spread it across the surface starting from the deep end: this protects the pool finish and speeds up mixing. These steps are part of the weekly routine, and we set out that routine step by step in our article on how to maintain a pool.

On the Çeşme peninsula the season is long and the sun is intense, and that feeds straight into dosing. Ultraviolet light breaks down part of the chlorine in the water through the day; as water temperature rises, organic load multiplies faster and chlorine is used up more quickly. Heavy use adds to it: a weekend with guests puts far more chemical demand on a pool than a quiet week. The imbat and lodos winds, meanwhile, carry a constant film of dust, salt and plant debris onto the surface, occupying part of the chlorine before it does anything else.

The practical consequence is this: your dosing rhythm in July and August will not be the same as in May. What changes is not the dosage on the label but how often you measure and how frequently you top up. In midsummer you need to check free chlorine more often, keep an eye on the stabiliser and catch situations that call for shock treatment early. Topping up when the sun affects chlorine least, in the cool of the evening, also gets more out of the same product. That is exactly why, in the pools we maintain in Alaçatı, we shorten the interval between tests during the busiest weeks of the season.

Pool chemicals are safe when used correctly, but a few rules are not open to debate. The most important is never to mix two chemicals with each other: using the same bucket, the same measuring cup, or applying them one after another at the same spot can all trigger dangerous reactions. Second, the chemical always goes into the water, never water onto the chemical. Applying in the evening where possible both keeps the sun from wasting the product and gives the water a full night of circulation for even distribution.