Pool Water Chemistry Cheat Sheet

Why one page of numbers matters more than it looks

Most pool problems that show up as visible symptoms — cloudy water, a burning chlorine smell, scaling on tile, a liner slowly degrading — trace back to one or two of these numbers sitting outside range for weeks without anyone noticing. None of them cause a dramatic, obvious failure on their own. They just quietly push everything else in the wrong direction until a symptom finally shows up, usually the cloudy water or algae problem that gets all the attention. Keeping this page bookmarked and actually testing against it regularly is the difference between chasing symptoms constantly and rarely having a problem in the first place.

The ranges below are the same targets pool professionals use and are close to universal across residential pool types — chlorine, saltwater, above-ground, and inground. The one caveat: manufacturer guidance for a specific liner, finish, or heater can occasionally narrow a range further, so treat these as the reliable general standard rather than an absolute override of your equipment's own documentation.

The ideal ranges, all in one table

Free chlorine: 1–4 ppm for a standard chlorine or salt pool. This is your active sanitizing power — the chlorine that's actually available to kill bacteria and oxidize contaminants right now, as opposed to chlorine that's already been used up.
Combined chlorine: Should be as close to 0 ppm as possible, and never above 0.2 ppm. This is "spent" chlorine bound to contaminants (chloramines) — it's what causes the strong chemical smell people mistake for too much chlorine.
pH: 7.4–7.6. Below 7.2 starts corroding metal equipment and irritating eyes; above 7.8 sharply reduces how effective your chlorine actually is and starts causing scale.
Total alkalinity: 80–120 ppm. This is pH's buffer — the thing that keeps pH from swinging wildly every time something else changes it. Low alkalinity means pH bounces around unpredictably; high alkalinity makes pH stubborn and hard to adjust.
Calcium hardness: 200–400 ppm (175–225 ppm for vinyl or fiberglass pools, which are more scale-sensitive). Too low and the water becomes aggressive, pulling calcium out of plaster and grout instead; too high causes visible scaling on surfaces and equipment.
Cyanuric acid (CYA / stabilizer): 30–50 ppm for outdoor pools (protects chlorine from UV breakdown), 0 ppm or minimal for indoor pools that don't need UV protection. Above 80 ppm, chlorine's effectiveness drops enough that a normal free chlorine reading no longer means what it should — see "chlorine lock" below.
Salt (salt pools only): 2,700–3,400 ppm for most residential salt chlorinators, though always check your specific cell manufacturer's target — this varies more between brands than the other ranges here.

How these numbers actually affect each other

This is the part most quick-reference charts skip, and it's the part that actually matters for troubleshooting. These parameters aren't six independent numbers — they're a connected system where moving one deliberately moves at least one other as a side effect.

pH and chlorine effectiveness

Chlorine exists in water as two forms — hypochlorous acid (the active, effective form) and hypochlorite ion (a much weaker form) — and the ratio between them is controlled almost entirely by pH. At pH 7.5, roughly half your chlorine is in the strong form. By pH 8.0, that drops to around a quarter. This is why a pool can have a "normal" free chlorine reading and still struggle with algae or cloudiness — the reading counts both forms equally, but only one of them is doing real work.

Alkalinity and pH

Total alkalinity is essentially a buffer that resists pH change. This is genuinely useful — it stops pH swinging every time rain falls, swimmers get in, or chlorine is added — but it also means alkalinity has to be corrected first before pH adjustments will hold. Adjusting pH while alkalinity is still out of range is a common reason pH "won't stay" where it's set.

Cyanuric acid and chlorine lock

CYA protects chlorine from being burned off by UV, which is genuinely necessary outdoors — unprotected chlorine can lose most of its strength in a few hours of direct sun. But CYA also binds to chlorine and reduces how reactive it is. High CYA (usually from repeated dichlor or stabilized-tablet use without dilution) can leave chlorine so weakened that even a technically-in-range free chlorine reading isn't sanitizing effectively — this "chlorine lock" is one of the most common causes of a pool that won't clear despite chlorine numbers looking fine.

Calcium hardness, alkalinity and pH together (the saturation balance)

These three, along with water temperature, determine whether water is scale-forming, corrosive, or balanced — sometimes summarized as the Langelier Saturation Index by pool professionals. It's why a pool can have a "normal" pH but still slowly scale or corrode if calcium hardness and alkalinity are pulling it out of overall balance. For most residential pools, keeping all three individually in range is enough without calculating the full index — but it's worth knowing they interact, not just sitting in isolation.

The correct order to balance a pool

Testing everything at once and dosing chemicals in whatever order is convenient is how one fix quietly undoes another. This is the order that actually works, because each step is affected by the one before it:

Total alkalinity first

Correct alkalinity before touching pH — since alkalinity buffers pH, adjusting pH first just means you'll likely need to redo it once alkalinity moves. Raise low alkalinity with sodium bicarbonate; lower high alkalinity with muriatic acid or dry acid, added slowly and retested.
pH second

With alkalinity in range, pH adjustments will actually hold. Raise low pH with soda ash; lower high pH with the same muriatic acid or dry acid used for alkalinity, since both parameters respond to the same acid — just in different doses.
Calcium hardness third

Doesn't interact as directly with the first two, but correcting it after pH and alkalinity are settled avoids compounding scale or corrosion risk while other numbers are still shifting. Raise with calcium chloride; lowering it usually means partially draining and refilling with lower-hardness water, since there's no chemical that removes calcium.
Cyanuric acid fourth

Raise with cyanuric acid (stabilizer) directly, or it builds up gradually from dichlor and stabilized tablets. There's no chemical fix for high CYA — the only way down is dilution, partially draining and refilling with fresh water.
Sanitizer (chlorine) last

Once the other four are in range, chlorine dosing actually works the way the label predicts — the same dose in a poorly balanced pool can behave completely differently. This is also the point to shock if needed; see our shocking guide for the full process.

What each common chemical actually does

Sodium bicarbonate (baking soda): Raises total alkalinity, with a smaller secondary effect of raising pH. The standard choice for low alkalinity.
Soda ash (sodium carbonate): Raises pH directly, with a smaller secondary effect on alkalinity. Used when pH specifically is low but alkalinity is already fine.
Muriatic acid / dry acid (sodium bisulfate): Lowers both pH and alkalinity — the main tool for bringing either or both down. Muriatic acid is liquid and faster-acting; dry acid is granular and easier to store and handle safely.
Calcium chloride: Raises calcium hardness. No practical effect on pH or alkalinity at normal dosing.
Cyanuric acid (stabilizer): Raises CYA specifically. Slow to dissolve — pre-dissolving or using a feeder speeds this up and avoids it settling undissolved on the pool floor.
Chlorine (liquid, granular, tablets): Raises free chlorine. Different forms carry different side effects — see our shocking guide for how cal-hypo, dichlor, lithium hypochlorite and non-chlorine shock each affect other parameters differently. Plain household bleach also works in a pinch — see our bleach vs pool chlorine guide for the dosing math.

Testing frequency that actually catches problems early

Free and combined chlorine, pH: 2–3 times a week during active swim season — these move fastest and matter most for day-to-day water safety and comfort.
Total alkalinity: Weekly — changes more slowly than chlorine and pH but still meaningfully within days.
Calcium hardness and CYA: Monthly is usually enough, since both change slowly under normal conditions and mainly drift from specific events (fresh fills, evaporation, repeated stabilized-chlorine use) rather than daily use.
Everything at once: After heavy rain, a significant water top-up or partial drain, opening the pool for the season, or any time something seems off that a single-parameter test doesn't explain.

A basic test strip is fine for routine mid-week checks, but a liquid reagent kit (like a Taylor or Lamotte kit, the type most pool shops use behind the counter) is meaningfully more accurate for chlorine and pH specifically — worth using for the twice-weekly core tests even if strips cover the monthly extras.

Reading a test result you don't understand

Chlorine reads high, but there's still a strong smell

This is a combined chlorine (chloramine) problem, not a free chlorine one — test them separately rather than relying on a total chlorine number, which lumps both together and hides exactly the distinction that matters. See our chlorine smell guide for the full explanation.

pH keeps drifting back up within a day or two

Almost always a sign alkalinity is still high, or aeration from a waterfall, spa jets, or a fountain feature is pushing pH up as a side effect (this is a genuine, common cause — aerating water naturally raises pH over time). Check alkalinity before assuming the pH dose itself was wrong.

Everything tests in range but the water still looks cloudy or dull

Chemistry can be balanced while filtration or circulation is the actual problem — check filter run time and cleanliness before assuming a chemistry cause. Our cloudy water guide walks through the full diagnostic order, and our pump and filter troubleshooting guide covers the equipment side specifically.

Common questions

What's the single most important number to get right?

pH, because it's the one parameter that quietly degrades almost everything else — it determines how effective your chlorine actually is, how fast surfaces and equipment corrode or scale, and swimmer comfort. Alkalinity matters just as much, but mainly because it's what keeps pH from swinging in the first place.

Why does my chlorine read fine but the pool still has problems?

A normal free chlorine number doesn't guarantee it's working at full strength — high pH, high cyanuric acid, or high combined chlorine (chloramines) can all leave your actual sanitizing power well below what the reading suggests. Chlorine level alone is only half the picture.

How often should I actually test my pool?

Free and combined chlorine plus pH, 2–3 times a week during swim season. Alkalinity weekly. Calcium hardness and cyanuric acid monthly, since they change slowly — the main exception is right after a big rain event, a fresh water top-up, or opening the pool for the season, when it's worth testing everything at once.

Can I just add a bit of everything and call it balanced?

No — several of these chemicals work against each other if added out of order or without testing first. Raising alkalinity pushes pH up as a side effect; raising calcium hardness does nothing for sanitizing but can cause scaling if overdone. Test first, then dose one parameter at a time in the correct order, covered above.

Do saltwater pools need to worry about all of this too?

Yes, every parameter on this page still applies to a salt pool — the salt cell just replaces manual chlorine dosing, it doesn't change pH, alkalinity, calcium hardness, or CYA management at all. See our salt vs chlorine guide for more on how the systems differ day to day.