What is the ideal pH for a pool in Cyprus — and why we don't just look at pH

Start with the official answer

The Pool & Hot Tub Alliance (PHTA) — the leading professional pool industry body in North America — publishes recommended ranges for pool water chemistry that are used worldwide as the baseline:

These numbers are solid. They are established, peer-reviewed, and used by professionals around the world. We follow them as a starting point.

But when we started maintaining pools in Cyprus, following these numbers alone was not enough. The water didn’t cooperate the way the textbook said it should — and figuring out why changed how we work.

The problem we couldn’t explain

In our first season, we were doing everything by the book. We tested pH. We tested chlorine. We adjusted. We came back the following week and adjusted again.

pH kept climbing. Every week, without fail, the readings were high. We added acid. It came back up. We added more acid. Same result.

We were not making mistakes. The chemistry was not being neglected. But the water was not cooperating — and we didn’t fully understand why.

That’s when we started asking questions we hadn’t asked before.

Henry’s Law: why pH always wants to rise

The first answer came from basic chemistry — specifically, Henry’s Law.

Henry’s Law describes how gases dissolve in liquids and, critically, how they escape. Carbon dioxide (CO₂) is naturally dissolved in pool water, and it plays a central role in pH stability. CO₂ in water forms carbonic acid, which keeps pH from climbing. But CO₂ is volatile — it wants to leave the water and return to the atmosphere.

Every time water is agitated — splashing, swimming, jets, waterfalls, even wind — CO₂ escapes. As it does, carbonic acid disappears, and pH rises. This is not a malfunction. This is physics.

pH drift upward is the natural state of pool water. It is not a sign that something is wrong. It is inevitable.

This means something important: if your pool’s pH is consistently low and needs to be raised — something unusual is happening. You may be fighting the water rather than working with it. In normal, well-managed pool water, the challenge is almost always the opposite: keeping pH from rising too quickly, not trying to push it up.

Understanding this changed how we think about every pH reading we take.

The question nobody was asking: why is pH just one number?

We kept returning to the same problem. pH alone wasn’t telling us enough. A reading of 7.8 could mean very different things depending on the temperature, the calcium content, the alkalinity, and what was dissolved in the water.

We needed a framework that looked at the whole picture — not individual numbers in isolation.

That’s when we found Orenda Technologies.

Orenda is a US-based water chemistry company built around a simple but radical idea: pool water should be managed as a system, not as a checklist of individual parameters. Their methodology is built on the Langelier Saturation Index — a formula created by water engineer Wilfred Langelier in 1936 and now used in municipal water treatment around the world.

We read their material. We studied the science. We asked hard questions. The answers made sense in a way that standard pool chemistry never quite had.

We began applying the Orenda approach to every pool we manage. PHTA remains our starting baseline, but Orenda’s methodology is what we use day to day.

Two sources, one decision: which LSI range we use

Here’s a practical example of where PHTA and Orenda differ — and which we follow.

• PHTA recommended LSI range: −0.3 to +0.5
• Orenda recommended LSI range: −0.3 to +0.3

Both are professional, defensible numbers. PHTA allows a wider positive margin; Orenda is more conservative on scale formation. We use Orenda’s tighter ±0.30 range because in Cyprus conditions — hard tap water, high summer temperatures, intense evaporation — a pool sitting at LSI +0.4 is one weekend of wind and pH drift away from scaling. The tighter range gives us a buffer we’ve learned to need.

What LSI actually measures — and what pH doesn’t

The Langelier Saturation Index (LSI) is not a replacement for pH. It is a calculation that puts pH in context.

LSI combines six parameters:

• pH
• Total Alkalinity
• Calcium Hardness
• Cyanuric Acid (CYA)
• Water Temperature
• Total Dissolved Solids (TDS)

The result tells you whether your water is balanced (LSI near 0.00), aggressive (negative LSI — water attacks surfaces and equipment), or scale-forming (positive LSI — water deposits calcium on surfaces, filters, and fittings).

Here is the critical point that most pool advice gets wrong:

pH does not make water scale-forming. LSI does.

A pH of 7.8 is not inherently problematic. It only becomes a problem if the full LSI calculation — including temperature and calcium hardness — pushes the index into positive territory. Conversely, a pH of 7.4 can exist alongside a negative LSI if calcium hardness is low and temperatures are cold. That water is aggressive, even though the pH looks perfect.

We’ve written about this dynamic in detail in our piece on Paphos hard water and why high calcium isn’t the enemy. Tap water in Paphos generally runs around 200–260 ppm calcium hardness, but pools climb well above that over time through evaporation and the use of calcium hypochlorite. Combined with summer temperatures past 30°C and the natural pH drift from Henry’s Law, the LSI in a Cyprus pool can move quickly — which is why managing pH alone, without LSI, means you may be constantly reacting to a symptom while the underlying imbalance continues undisturbed.

A note on HOCl and CYA — what matters for Cyprus outdoor pools

There is widespread advice that high pH is dangerous because it reduces the effectiveness of chlorine. The mechanism behind this is real: as pH rises, free chlorine shifts from hypochlorous acid (HOCl — the active sanitising molecule) to hypochlorite ion (OCl⁻), which is far less effective.

The widely cited figures (calculated for 25°C, no CYA):

• At pH 7.4, roughly 62% of free chlorine is in the active HOCl form.
• At pH 7.8, that drops to around 33%.

This sounds alarming. But here is what that advice almost always omits: this relationship between pH and HOCl applies in this form only in the absence of cyanuric acid (CYA).

CYA — also called stabiliser or conditioner — is standard in every outdoor pool in Cyprus. It protects chlorine from UV degradation, but it also fundamentally changes the chlorine chemistry. In a CYA-dosed pool, the relevant metric is the FC/CYA ratio, not the HOCl-pH curve calculated for CYA-free water. This is why our tracking system uses one combined metric instead of two — the %HOCl(2025) column in our data is our FC/CYA calculation, which gives the genuinely active chlorine percentage for a stabilised pool. We covered the mechanics of this in our piece on why chlorine “stops working” in Cyprus pools.

In practical terms: for outdoor pools in Cyprus with normal CYA levels, the concern about pH at 7.8 or even 8.0 reducing HOCl is significantly overstated. What does matter is the threshold of pH 8.2 — above that level, HOCl activity drops meaningfully even in the presence of CYA, and that is the point where we take action.

Below 8.2, if LSI is balanced and the FC/CYA ratio is correct, a pH reading of 7.9 or 8.0 is not a crisis. It is normal pool water doing what pool water does.

To be clear: we are not recommending keeping pH high. We are recommending evaluating pH only in the context of LSI and HOCl together — not as a standalone number that triggers automatic acid addition.

“But high pH irritates eyes and skin” — does it?

This is one of the most persistent myths in pool management. If swimmers are experiencing eye irritation, red skin, or discomfort, the instinct is to blame pH. But in a properly chlorinated pool, these symptoms are almost never caused by pH in the 7.6–8.0 range.

The real culprit is almost always chloramines — compounds formed when chlorine reacts with nitrogen from sweat, urine, and other organic matter. Chloramines are irritating, they smell, and they are a sign of chlorine demand, not high pH.

If your swimmers are uncomfortable, check combined chlorine (chloramines) before reaching for acid. A pH of 8.0 with zero chloramines is a more comfortable pool than a pH of 7.4 with high combined chlorine.

This is exactly the kind of distinction that gets lost when you manage water by individual numbers rather than as a system.

Our data: before and after LSI management

These are real measurements from one of our client pools. Weekly visits, photometric analysis, consistent conditions.

One note on terminology before reading the data. The column labelled %HOCl(2025) in our tracking system is our calculation of the FC/CYA ratio — not the traditional HOCl percentage from the pH dissociation curve. We’ve folded them into one metric because, in a CYA-stabilised pool, they refer to the same thing: the proportion of free chlorine that is actually available to disinfect. The traditional HOCl-pH table calculated for CYA-free water doesn’t apply to outdoor Cyprus pools, where CYA is always present. So when you see “ %HOCl” in our data, read it as “FC/CYA ratio” — the genuinely active chlorine percentage in a stabilised pool.

Before LSI was established

In the early phase of monitoring, our LSI formula was not yet receiving all required inputs — temperature, CYA, and TDS data were incomplete. During this period:

What the data shows: pH readings ranged from 7.55 to 8.12 across consecutive visits. Total alkalinity bounced between 77 and 145 ppm. Acid was added on every visit. One row shows pH dropping to 5.12 after acid addition — this was a deliberate technique to reduce alkalinity that had climbed to 145 ppm (well above the recommended range), not an error. The aggressive acid dose reduces alkalinity quickly, and aeration brings pH back up afterwards.

pH was fluctuating week to week. Acid was added on every visit. %HOCl was inconsistent. The water was being managed reactively — we responded to what the numbers showed, without understanding the system behind them. Alkalinity was high and difficult to bring under control. The water had no stable baseline.

After LSI was established and balanced

Once all parameters were tracked and LSI was functioning:

What the data shows: LSI readings of 0.01 and 0.12 — both comfortably within Orenda’s ±0.30 safe range. pH stabilised between 7.62 and 8.23 without forced correction. Alkalinity changes on most visits: zero. The water reached its own equilibrium and stayed there.

This is what working with water looks like — not fighting it.

So what is the ideal pH for a Cyprus pool?

The PHTA range of 7.2–7.8 is a good starting point. We don’t ignore it.

But in Cyprus conditions — high evaporation, high summer temperatures, year-round outdoor use — the pH number alone will mislead you. What matters is the whole picture:

• Is LSI in range (Orenda’s ±0.30)?
• Is the FC/CYA ratio appropriate for the bather load and UV exposure?
• Is pH drifting up naturally (expected and manageable) or being pushed in an unusual direction?
• Are you managing the water, or reacting to it week after week?

A pH of 7.9 with LSI at 0.05 is better managed water than a pH of 7.4 with LSI at +0.7.

The number is not the answer. The system is.

What we do differently

At Pool Health, every pool visit includes:

• Photometric analysis (not test strips)
• Full LSI calculation incorporating temperature, CYA, calcium hardness, and TDS
• FC/CYA ratio (the genuinely active chlorine percentage — what we track as %HOCl in our system)
• Weekly data logged and trended over time

We don’t just take readings. We maintain a water history for each pool — because water chemistry is not a snapshot, it’s a story. And understanding the story is what allows us to stop reacting and start managing.

If you’d like a chemistry audit for your pool, our full-scope inspection service covers all of the above and gives you a written report. For ongoing care, see our maintenance programme.

Sources & references

1. Pool & Hot Tub Alliance (PHTA). ANSI/PHTA-1 American National Standard for Public Pools and Recommended Water Chemistry Parameters. Source
2. Orenda Technologies. The Langelier Saturation Index Explained. Source
3. Orenda Technologies. Chlorine, pH, and Cyanuric Acid: Why Free Chlorine Is Not Created Equal. Source
4. Langelier, W. F. (1936). The Analytical Control of Anti-Corrosion Water Treatment. Journal AWWA, Vol. 28, No. 10. Original formulation of the LSI.
5. Wojtowicz, J. A. (2001). Effect of Cyanuric Acid on Swimming Pool Chemistry. Journal of the Swimming Pool and Spa Industry.
6. CDC. Disinfection & Testing — Effect of pH on Free Chlorine. Source