Salt Water Pool Chemistry: Why the pH Climbs, and What to Set the Cell At
A salt pool is a chlorine pool that makes its own chlorine, and making the chlorine and then using it up is pH-neutral over a full cycle — as long as the chlorine dissolves. The pH still climbs, mostly because pool water is massively over-carbonated compared to air and CO₂ leaks out through the surface — at TA 80 and pH 7.5 the water holds about 7 times the carbon dioxide it would hold in balance with air. Your carbonate alkalinity sets the pH your pool is climbing toward: about 8.21 at 60 ppm, 8.33 at 80, 8.49 at 120, rising 0.30 pH for every doubling. That is why the fix is to run alkalinity at the LOW end — Trouble Free Pool targets TA 60 for salt pools — and to stop chasing pH down, because a lower pH outgasses faster. The cell's own share, if it has one, is the one Richard Falk suspected when he retracted the popular hydrogen-bubble theory in 2008: chlorine gas escaping at the return before it dissolves, which takes acid out of the water. He suggested pointing the returns downward and asked owners to test it; nobody has published the result. Turning the cell down is not a pH lever — you need that chlorine either way. Targets that genuinely differ from a chlorine pool: CYA 60–80 (against 30–50), and at the same CYA a salt pool needs LESS free chlorine than a liquid-chlorine pool, because the cell doses all day instead of once. Set the cell by testing FC at the same time each day and adjusting output or pump run time until it holds; check your own manual for a starting point, and treat another owner's percentage as meaningless, because it belongs to a different cell and schedule.
A salt water pool is a chlorine pool. The cell makes the chlorine instead of you pouring it, and that is the entire difference in what is sanitising your water — if that is news, start with are salt pools chlorine-free? and do I still have to test a salt pool? (yes).
What genuinely differs is the operating pattern: the chlorine arrives continuously instead of in a daily slug, a few targets shift because of that, and the pH climbs steadily enough that acid becomes a routine purchase. That last part is the thing owners ask about most, and it is where almost every explanation in circulation is wrong — including one we used to repeat on this site.
Why the pH climbs (and why the popular answer is wrong)
Making chlorine and using it up is pH-neutral — if the chlorine dissolves. Inside the cell, one plate makes acid and the other makes base; when the chlorine is later used up, what was borrowed is returned. Richard Falk, the chemist whose work underpins most of what the hobby knows about this, put it plainly in 2007: “the addition of hypochlorite or the production of chlorine in an SWG plus the later usage of that chlorine is a pH neutral process.” So the first folk explanation — that the cell’s high-pH byproduct pushes the pool up — is cancelled out by its own other half.
The second folk explanation has a better pedigree and is still wrong. In that same 2007 post, Falk proposed that the hydrogen bubbles a cell produces aerate the water on the way out and strip its dissolved CO₂, and that this was “the main cause of pH rise in SWG pools.” It is the version you will find repeated across forums, retailer blogs and at least one respected industry educator to this day.
He retracted it eight months later. In June 2008 he ran the gas volumes and posted the result:
I calculated whether the SWG produces enough hydrogen gas bubble volume to have the small amount of carbon dioxide that would be allowed into it (via Henry’s Law for equilibrium) to make the pH rise. It isn’t enough and that’s under ideal conditions with full equilibrium reached… the volume just isn’t enough.
What he said next is the part that usually gets dropped. He did not conclude the cell adds nothing. He went back to the explanation he had opened the thread with: “I’m back to leaning towards the other explanation I originally started with in this post in this thread where I thought it might be undissolved chlorine gas bubbles.” Chlorine gas that escapes out of the return before it dissolves takes acid out of the water with it, which is the one way the cell itself can push pH up — the “pH-neutral” cycle above only holds for chlorine that stays in the pool. He suggested pointing the returns downward “to give the bubbles a greater chance of dissolving more completely”, asked owners to try it, and summed up one owner’s case as “could just be regular carbon dioxide outgassing without much change from the SWG itself — that is, the SWG effect may mostly be chlorine gas escaping.”
So the retraction swapped one cell mechanism for another; it did not clear the cell. He never went back to correct the 2007 post, which is why the hydrogen version is the one that spread. Neither the arithmetic behind the retraction nor a test of the chlorine-gas idea was ever published, so take it for what it is: the person who originated the theory calculated it, reversed himself, and left the replacement as a hypothesis.
Most of what is happening is not salt-specific at all. Pool water is grossly over-carbonated compared to the air above it — at TA 80 and pH 7.5, about 7.2 times the CO₂ it would hold in balance — so carbon dioxide leaks out through the surface, and every molecule that leaves takes an acid with it. That runs in every pool ever built, and it is the part your alkalinity controls; escaping chlorine gas, if Falk was right, is a salt pool’s extra. We cover it generally in why pool pH rises. What makes it feel like a salt problem is that salt pools tend to run on pads with waterfalls and spillovers, and tend to run the pump long hours to make chlorine — and aeration and runtime are both on the list of things that speed it up.
Your alkalinity sets the ceiling you are climbing toward
This is the part that changes how you run the pool. Falk’s 2014 conference deck lists as a fallacy that “Total Alkalinity (TA) Stabilizes pH,” and gives the correction: “TA is a SOURCE of rising pH.” His table puts the equilibrium pH — the value your pool is heading for and will sit at once CO₂ stops leaving — against carbonate alkalinity:
| Carbonate alkalinity | The pH your pool climbs toward |
|---|---|
| 20 ppm | 7.75 |
| 40 ppm | 8.04 |
| 60 ppm | 8.21 |
| 80 ppm | 8.33 |
| 100 ppm | 8.42 |
| 120 ppm | 8.49 |
It is a clean logarithmic relationship: the ceiling rises about 0.30 pH for every doubling of carbonate alkalinity. Lower the alkalinity and you lower the ceiling and slow the climb toward it at the same time — Falk’s slides put the reduction in outgassing at 25% or more going from TA 80 to 60, and note that outgassing rates vary as the square of the alkalinity.
One catch that trips up careful owners: that is CARBONATE alkalinity, and your kit reports TOTAL. Cyanuric acid and borate both titrate as alkalinity and neither one carries any carbon dioxide, so neither contributes to this. A pool testing TA 90 with CYA at 70 has roughly 67 ppm of the alkalinity that actually drives pH — and a real ceiling nearer 8.25 than 8.4.
So the salt-pool discipline is: alkalinity low, pH high, and stop chasing
Trouble Free Pool’s salt-specific guidance follows straight from the chemistry above, and it is close to the opposite of what most owners are told:
- Target TA 60. Not the 80–120 the industry prints — that number assumes acidic trichlor pucks you are not using.
- Do not chase pH down. TFP is blunt: “Don’t ‘chase’ pH down to 7.2, this will cause rapid pH rise.” A lower pH means more dissolved CO₂ and faster outgassing, so every trip to 7.2 buys you a faster climb back.
- While TA is still high, let pH drift and dose in bigger steps. “If your TA is above 60, let pH rise naturally to 8.0-8.2, then add muriatic acid to lower it back into the mid-7s.” Acid lowers TA as well as pH, so this walks your alkalinity down for free.
- Once TA is 60, stop going that low. “Keep your pH 7.8 to 8.0 before lowering and only lower to 7.8.”
- Turn off the waterfall. Aeration is on the short list of what actually drives the rate. The cell setting is not.
- Try pointing your returns downward. This is Falk’s suggestion for the chlorine-gas share: it gives the bubbles longer to dissolve. It is untested in anything published, so treat it as an experiment — watch whether your acid demand changes over a couple of weeks, and weigh it against surface skimming, which he noted works better with returns pointed up.
One point is worth stating plainly, because it is the most common wasted move: turning your cell output down is not a pH lever. Most of the rise tracks over-carbonation and aeration. Whatever share the cell adds comes with the chlorine your pool needs anyway, so turning it down just gives you less chlorine.
The numbers that differ from a chlorine pool
Most of your five numbers are the same as any pool — start at the five numbers if you want the full set. These are the ones salt changes:
| Number | Salt pool | Chlorine pool | Why salt differs |
|---|---|---|---|
| CYA | 60–80 | 30–50 | The cell doses all day, so algae risk is lower and the sun protection pays for itself in cell life |
| Free chlorine | Less, at the same CYA — see below | More | Continuous dosing means no trough between doses to defend |
| Total alkalinity | 60 | 60–80 | Lower ceiling, slower climb, less acid |
| pH | 7.2–8.0, run the top half | 7.6–7.8 | Chasing it down accelerates the rise |
| Salt | Your cell maker’s range, targeted just above the middle | n/a | It is the raw material; the range is per-cell |
| Calcium hardness | By surface, same as any pool | By surface | But high CH plus high pH scales the cell first |
One honest note on that CYA row: the cell makers’ own manuals (Pentair’s, CircuPool’s and Hayward’s current ones) print 30–50. We run salt pools at 60–80 anyway, because a cell makes its chlorine slowly all day and the extra stabilizer keeps the sun from burning it off before it works; Trouble Free Pool runs salt pools higher for the same reason.
The free-chlorine one surprises people, so here it is in the makers’ own numbers. At CYA 70, Trouble Free Pool’s chart targets 8–10 ppm for a liquid-chlorine pool and 5–10 ppm for a salt pool, with the salt minimum at 3 rather than 5. A salt pool needs less chlorine at the same stabiliser level, because it never has to survive the gap between one day’s pour and the next.
What should your chlorine be?
Free chlorine is a ratio, not a fixed number. Enter your CYA and read your floor, target band, and SLAM level — add your current FC for a verdict.
Don't know your gallons? Work it out here →
Exact geometry at 7.48 gal/ft³. Kidney shapes, diving hoppers and salt/turnover figures live in the full Pool Volume Calculator.
Straight off Trouble Free Pool's FC/CYA chart (minimum ≈ 7.5% of CYA, SLAM ≈ 40%), snapped to the nearest published row — the chart table stays the source of truth. Doses assume 12.5% liquid chlorine; for cal-hypo, dichlor or trichlor use the chemical calculator, which runs the same math. CYA way over 100? More chlorine isn't the fix — lowering CYA is.
A note for anyone just switching on a new cell. TFP suggests an on-ramp rather than jumping straight to the target: raise CYA only to 60 and aim at the top of the FC range while you learn the cell, because “If you happen to get algae while learning the output of the cell, a SLAM (to clear algae) is much cheaper/easier with CYA at 60.” Sixty is already inside the 60–80 band; move up within it (TFP itself settles at 70–80) once you can hold the level. And if your CYA has drifted past 90, that is genuinely too far — chlorine gets hard to maintain and the only real fix is dilution, which is its own guide.
What to set the cell at
The output percentage is a share of your pump’s run time, not a strength. Pentair’s IntelliChlor guide puts it plainly: “at 100% the cell works all the time while the pool pump is running. When set at 80%, the cell is allowed to rest 20% of the time.” Jandy’s manual says the same, and Hayward runs its cell on a three-hour cycle, producing for half of it at 50%. So the chlorine you get is your cell’s rated output, times the percentage, times the hours the pump runs. That is why another owner’s percentage tells you nothing about your pool: theirs is a different cell, volume, run schedule and sun.
It also means the setting can be worked out, not guessed. Put in your cell, your pool and your pump hours:
What should your salt cell be set to?
Pick your cell, your pool and how long the pump runs. We work out the output percentage that replaces the chlorine your pool loses in a day, then show what your cell's own manual says about where to start.
Don't know your gallons? Work it out here →
Exact geometry at 7.48 gal/ft³. Kidney shapes, diving hoppers and salt/turnover figures live in the full Pool Volume Calculator.
Every maker’s manual also tells you where to start, and they do not agree, not even within one brand: Pentair’s original IntelliChlor guide says 60%, while its current IntelliChlor Plus and LT manual gives no starting number at all. We read each manual on 16 September 2026:
| Cell line | Manual's starting setting | What the percentage controls, in the maker's words | Source |
|---|---|---|---|
| Hayward AquaRite (TurboCell T-3, T-9, T-15) | About 50% "To find the optimum "Desired Output %" setting, start at approximately 50%." | "The output percentage of our system operates on a simple 3-hour cycle. If you set it to 100%, the cell will be active for the entire 3-hour cycle. If you set it to 50%, the system will produce for 1.5 hours, rest for 1.5 hours" | AquaRite Owner's Manual 092540 RevG, p. 9; the cycle wording is Hayward Support's answer on its W3T-CELL-15 product page |
| Pentair IntelliChlor (IC15, IC20, IC40, IC60) | 60% "Set the Sanitizer Output to 60% by pressing the MORE or LESS button" | "at 100% the cell works all the time while the pool pump is running. When set at 80%, the cell is allowed to rest 20% of the time while the pool pump is running" | IntelliChlor Installation and User's Guide, P/N 520589 Rev. R (8/7/23), pp. 15-16 |
| Pentair IntelliChlor Plus and LT (Plus30/40/60, LT15/25) | No starting number: raise output below 2 ppm free chlorine, lower it above 4 "IF FREE CHLORINE LEVEL IS BELOW 2 PPM: INCREASE Output Percentage" | "Cell Output Percentage is the percentage of time the SCG cell will produce chlorine while the pump is running." | IntelliChlor Plus/LT manual, P/N 523854 REV. B (6/25/25), p. 21 |
| CircuPool RJ Plus (RJ-30, RJ-45, RJ-60) | 75% "To find the optimum Chlorine Output setting, start at a setting of 75% and adjust as needed over the initial start up period." | "this simply indicates the system is in the resting portion of its duty cycle" | RJ PLUS Series manual 3300-7A (R202411), pp. 9 and 11 |
| CircuPool CORE (CORE-35, CORE-55) | 75% "To find the optimum Chlorine Output setting, start at a setting of 75% and adjust as needed over the initial start-up period." | "the system's power setting (the rate of chlorine production)" | CORE Series guide 4300-8A (R202411), pp. 10-11 |
| CircuPool EDGE (EDGE-15, 25, 40) | 75% (6 of 8 lights) "To find the optimum Chlorine Output setting, start at a setting of 75% (6 out of 8 blue lights)" | "the system's power level setting (the rate of chlorine production)" | EDGE Series manual 4300-7A (R202411), pp. 9-10 |
| Jandy AquaPure PureLink (PLC700, PLC1400) | 50% "Adjust the Chlorine Production to 50% by pressing the arrow buttons" | "at 100% the cell is on at all times while the pump is running. When the system is set at 90%, the cell will rest 10% of the time" | AquaPure PureLink manual H0325600 Rev F, pp. 34-35 |
| Jandy TruClear | 40% for 15,000 gal (57k L) and under; 60% for 25,000-30,000 gal (95–114k L) "A good starting point for pools at 15K gallons and under should be 40%. Pools closer to the 25K to 30K gallons should use 60% as a starting point." | "This controls the amount of run time for the cell." | TruClear manual H0613500 Rev C (2017), pp. 20-21, a dealer-hosted copy |
Hayward’s GLX-CELL-5 for above-ground pools is not in the calculator: Hayward lists its daily output as “N/A”. The Solaxx Saltron Mini is not either, because its control is a timer of hours per day that runs independently of your pump, not a percentage.
The method is what transfers, and it is what you will use to move off any starting number anyway:
- Get CYA and salt in range first. Tuning output against a moving stabiliser level is guesswork.
- Test FC at the same time every day while you tune. Early evening is the useful hour — it is usually the day’s low.
- Trending down? Raise output, or lengthen the pump run. Both add chlorine; run time is often the cheaper lever on a variable-speed pump.
- At 100% and still falling? That is one of four things: not enough run time, unusual chlorine demand worth investigating, CYA too low to protect what you make — or a cell that is simply too small.
On that last one, the makers and TFP agree in direction: buy more cell than you need. TFP’s recommendation is a cell rated for at least twice your pool’s volume. An oversized cell holds your chlorine at a low output percentage, which means fewer operating hours on the plates and a longer service life — the economics are in how long does a salt cell last, and the hardware itself is ranked in the salt chlorinator showdown.
Two seasonal notes that are not failures: the cell stops generating in cold water on purpose (the manuals put the cutoff around 50–52°F depending on brand), and in winter you dose by hand instead — see year-round chlorination in Florida if your pool never closes. And add salt with the cell switched off, which TFP flags specifically to avoid damaging it.
The number that decides whether your cell scales
“Everything is in range” does not mean the water is balanced, and a salt pool is where that bites first, because the water at the cell plates runs at a far higher pH than the pool does. The saturation index — LSI, or CSI in PoolMath — is the single number that says whether your water will deposit calcium or dissolve it, and we cover how to read it in water balance and the saturation index.
Two salt-specific points that guide does not make:
- TFP’s advice for salt pools is to keep the index slightly negative — “many SWG pools do best keeping CSI slightly on the negative side to reduce scaling tendency in the cell.”
- Salinity itself moves the index by roughly 0.2 units at 3,000 ppm, per Falk’s calculation. So run your index in something that takes a salt input. The cardboard wheel in a drop kit does not have one, which is the one place that otherwise-excellent tool reads a salt pool wrong.
If you are already fighting deposits, why a salt pool scales faster is the repair guide.
Borates: the buffer that works where alkalinity has quit
Alkalinity’s buffering is strongest around pH 6.3 — more than a full unit below where any pool operates — and it weakens exactly as your pH climbs into the 8s. Borate is the mirror image: boric acid’s pKa is about 9.1 in salt water, so its buffering gets stronger as pH rises. Wojtowicz’s published buffer-intensity tables put the crossover at about pH 7.8: below it carbonate does more work, above it borate does, and by pH 8.2 borate is several times stronger.
At 30–50 ppm that measurably slows the climb and blunts the high-pH spike inside the cell. But it is the second move, not the first — TFP is explicit that lowering TA is the more effective lever, and borate is a chemical that stays in the pool once added. Full treatment in borates in a pool. One testing note to carry with it: borate titrates as alkalinity, inflating your TA reading by roughly 5–7 ppm at pH 7.6 and around 17 ppm at pH 8.0 — so correct for it before you trust a TA number in a borated pool.
Two things salt does not do
Salt does not buffer your pH. Buffering comes from weak-acid pairs whose pKa sits near your operating range; sodium and chloride are a strong base and a strong acid, spectators at pool pH. Falk’s calculation puts the buffering effect of 3,000 ppm salt as small enough “to pretty much ignore.” What salt genuinely changes is ionic strength, and that lands on the saturation index, not on pH stability.
Salt does not make the pool self-regulating. The cell automates exactly one job. Everything on this page is still yours.
The weekly routine
- Twice a week: free chlorine and pH. Adjust cell output or run time for FC; add acid for pH, in the bigger steps described above rather than daily nibbles.
- Monthly: total alkalinity, calcium hardness, and salt — and your saturation index, which needs CH and TA anyway.
- Two or three times a season: CYA. It only leaves by dilution, so watch it drift up.
- Whenever the cell is out: look at the plates. Scale means your index and your pH have been running high.
Test it yourself with a drop kit — how to test your pool water covers which one and why strips will not settle these numbers. And if the water has already gone somewhere you did not intend, the pool is green starts the recovery.
Frequently asked
Why does the pH in my salt water pool keep going up?
Mostly for the same reason it rises in every pool. Pool water holds far more dissolved carbon dioxide than the air above it — at a total alkalinity of 80 and a pH of 7.5, about seven times more — so CO₂ steadily escapes through the surface, and pH rises as it goes. Making chlorine and then using it up is pH-neutral over a full cycle: the cell makes acid at one plate and base at the other, and using the chlorine up returns what was borrowed — as long as the chlorine dissolves into the water. The popular explanation, that hydrogen bubbles from the cell aerate the water and strip its CO₂, was published in 2007 by the chemist who devised it, Richard Falk, and retracted by him in 2008 after he ran the numbers: "It isn't enough… the volume just isn't enough." He went back to suspecting undissolved chlorine gas escaping at the return — gas that leaves before it dissolves takes acid with it — and suggested pointing returns downward, an idea nobody has published a test of. Either way, what you can control is your carbonate alkalinity, how low you hold your pH, and how much you aerate the water.
What should total alkalinity be in a salt water pool?
Lower than you have probably been told — Trouble Free Pool targets 60 ppm for a salt pool, against an industry habit of 80–120. The reason is that alkalinity is not a pH stabiliser in the direction that matters here; it is the reservoir of dissolved CO₂ that pushes pH up as it escapes. Falk's 2014 conference table puts a number on it: the pH your pool is climbing toward is about 8.04 at 40 ppm of carbonate alkalinity, 8.21 at 60, 8.33 at 80 and 8.49 at 120 — it rises about 0.30 pH for every doubling. Drop the alkalinity and you lower the ceiling and slow the climb at the same time; his slides put the saving at 25% or more going from 80 to 60. One catch: that table is CARBONATE alkalinity, and your test kit reports TOTAL. Cyanuric acid and borates both titrate as alkalinity and neither carries any carbon dioxide, so a pool testing 90 with CYA at 70 has closer to 67 ppm of the alkalinity that actually drives pH.
What should I set my salt cell output percentage to?
Start where your cell's manual says, then let a week of daily tests move you. The makers disagree: Hayward's AquaRite manual says to start at approximately 50%, Pentair's original IntelliChlor guide says 60%, Jandy's AquaPure manual says 50%, CircuPool's RJ Plus, EDGE and CORE manuals say 75%, Jandy's TruClear manual says 40% for pools of 15,000 gallons and under and 60% for 25,000 to 30,000, and Pentair's current IntelliChlor Plus and LT manual gives no starting number at all. The percentage is a share of the pump's run time, so the chlorine you get is the cell's rated output times the percentage times the pump hours; our calculator on this page works it out for your cell, pool and schedule. A number from another owner tells you nothing, because it depends on volume, cell size, pump run time, CYA, bather load, sun and season. Trouble Free Pool's method is the one to copy: with CYA at 70–80, target free chlorine of 5–10 ppm and never below 5, then test FC at the same time each day while you are tuning (early evening is a good choice, because it is usually the day's low). If FC trends down, raise the output percentage or lengthen the pump run. If you are at 100% and it still falls, you need more run time, or you have unusual chlorine demand worth investigating, or the cell is undersized — TFP recommends a cell rated for at least twice your pool's volume. One thing the setting will not fix: turning the cell down does not meaningfully slow your pH rise, because the rise is driven by alkalinity and aeration rather than by how much chlorine you made.
Does a salt pool need more chlorine than a regular chlorine pool?
Less, at the same stabiliser level — which surprises most owners. On Trouble Free Pool's chart, a liquid-chlorine pool at CYA 70 targets 8–10 ppm of free chlorine, while a salt pool at the same CYA 70 targets 5–10 with a minimum of 3. The reason is dosing pattern rather than chemistry: a salt cell adds chlorine continuously while the pump runs, so the water never rides the peak-and-trough cycle of a pool that gets one pour a day, and the risk of dipping below the algae threshold between doses largely disappears. That same logic is why salt pools run higher CYA — 60–80, against 30–50 on a chlorine pool — since the cell can afford the sun protection and the cell then works less to hold the level.
Do salt pools need borates?
They are optional, they are genuinely useful, and they are the second move rather than the first. Alkalinity buffers pH well below 7, which is nowhere near where a pool operates, and its grip weakens exactly as the pH climbs into the 8s. Borate is the opposite: boric acid's pKa is about 9.1 in salt water, so its buffering strengthens as pH rises. Wojtowicz's published buffer-intensity tables put the crossover at about pH 7.8 — below that, carbonate does more work; above it, borate does, and by pH 8.2 borate is several times stronger. At 30–50 ppm that measurably slows the climb and reduces scale inside the cell, where the water at the plates runs at a much higher pH than the pool does. But get total alkalinity to the low end first: TFP is explicit that lowering TA is the more effective lever, and borate is a chemical that stays in your pool once it is there. One testing note — borate titrates as alkalinity, so it inflates your TA reading, by roughly 5–7 ppm at pH 7.6 and around 17 ppm at pH 8.0.
Does the salt in the water buffer the pH?
No, and it is a common misreading of what salt does. Buffering comes from weak acid and conjugate base pairs — carbonate, cyanurate, borate — whose pKa sits near your operating pH and which can take up or release a proton. Sodium and chloride are a strong base and a strong acid: spectators, with no proton to trade at pool pH. What 3,000 ppm of salt genuinely changes is ionic strength, and Falk's calculation puts the buffering consequence at small enough "to pretty much ignore." The effect that IS material is on the saturation index, which the same calculation moves by about 0.2 units — which is why a salt pool's LSI or CSI has to be run with the salinity entered, and why the little calculator wheel in a drop kit, which has no salt input, reads a salt pool slightly wrong.