What should your pool chlorine level be?

With no stabilizer in the water, 2–4 ppm is enough.

Enter your CYA: minimum and target FC

A chart gives you the rule. The calculator gives you your number. The minimum FC is about 7.5% of your CYA reading (about 5% with a salt water generator), and at least 2 ppm once stabilizer is in the water. Type your stabilizer (cyanuric acid, CYA) reading and choose how you add chlorine. You get two numbers:

• Minimum FC: the level you should never drop below. Below it, chlorine may not keep up with algae and germs.
• Target range: where to aim after each dose, so FC stays above the minimum until the next one.

There is no shock level here. How much shock to add, and when you can swim again, come from your product's label, so follow its directions.

The calculator also estimates active chlorine (hypochlorous acid, HOCl) at the low end of your target. At CYA 40 and FC 3 that is about 0.029 ppm, a tiny share of the 3 ppm your test kit shows. If you add your current FC, it tells you whether you are low, in range, or too high. The table above lists every CYA level from 0 to 100 ppm, for regular chlorine and for salt pools.

Why 1–3 ppm isn't enough when you use stabilizer (MAHC 2024 Annex)

Your test kit measures FC. Only part of it is hypochlorous acid, the form that actually kills germs and algae. Stabilizer holds on to chlorine and releases it slowly, which protects it from sunlight but also keeps most of it inactive at any moment.

The Annex to the CDC's Model Aquatic Health Code (MAHC 2024, section 5.7.3.1.1.2) shows the effect with a table at pH 7.5 and 77 °F. Hypochlorous acid is about:

• 0.020 ppm when CYA is 20 times FC,
• 0.0097 ppm when CYA is 40 times FC,
• 0.0055 ppm when CYA is 70 times FC,
• 0.0038 ppm when CYA is 100 times FC.

What matters is the ratio, not either number alone. Our estimate for FC 2 with no stabilizer is about 0.97 ppm of hypochlorous acid; FC 2 with CYA 80 is about 0.0098 ppm, roughly a hundred times less. Same test result, very different pool. The MAHC Annex treats a CYA-to-FC ratio above 45 as a reason to close a public pool. That is why a fixed "1–3 ppm" rule works in unstabilized water and fails in most outdoor pools.

Where sources disagree: EPA labels vs FC/CYA ratio, and what we recommend

Source	What it says about FC
CDC (home pools)	at least 1 ppm without stabilizer, at least 2 ppm with it
EPA-registered pool product labels, PHTA	don't swim while FC is above 4 ppm; the MAHC Annex notes EPA has not approved pool products for use above 4 ppm with swimmers
MAHC 2024 Annex	the minimum should rise with CYA; 10 ppm is the upper limit
FC/CYA ratio principle (Trouble Free Pool community)	minimum about 7.5% of CYA, about 5% with a salt generator
An older EPA bleach label (2011)	0.6–1.0 ppm

We could read the ratio principle only through secondary sources, so we treat it as secondary and use our own parameterization rather than any published chart. Instead of choosing a side, we recommend avoiding the conflict: keep CYA at 30–40 ppm. At CYA 30 the minimum is 2.5 ppm; at CYA 40 it is 3 ppm. Both sit under the 4 ppm label limit, so you can follow the label and still have enough active chlorine. At CYA 50 the minimum is already 4 ppm, and above that no FC level satisfies both. Always follow the product label. How we built the rule is on the methodology page.

Salt water pools: lower minimum

A salt water chlorine generator makes chlorine all day in small amounts, so FC doesn't swing the way it does between manual doses. That is why the ratio principle allows a lower minimum, about 5% of CYA. Salt pools also run higher stabilizer to protect that steady production: Hayward's AquaRite manual allows up to 80 ppm. At CYA 70 the salt pool minimum is 3.5 ppm; at CYA 80 it is 4 ppm. The table above has both columns side by side. If your salt pool keeps drifting below the minimum, raise the cell output or pump hours rather than stabilizer. See what cyanuric acid does.

Hot tubs: 3–4 ppm (up to the limit on your label) and no CYA

Hot tubs follow different rules. The CDC sets a minimum of 3 ppm free chlorine (4 ppm for bromine), the MAHC Annex recommends 3–5 ppm chlorine or 4–6 ppm bromine, and the CDC advises against stabilizer in hot tubs at all. Many spa chlorine labels allow soaking only up to 4 ppm, so our hot tub calculators aim for 3–4 ppm unless you enter your label's own limit. Hot water, jets, and a few people in a few hundred gallons use chlorine up quickly, and with no CYA there is no ratio to track. Keep water at 104 °F or below. Doses in teaspoons are on the hot tub chlorine page.

Is 7.5 ppm chlorine too high?

For swimming, yes, with most products: pool chlorine labels usually say not to swim above 4 ppm, so wait and retest until FC is back at or below your label's limit. It is still under the 10 ppm upper limit in the CDC model code, and it comes down on its own with sun and time. For the water itself, 7.5 ppm is not too much if your CYA is very high: at CYA 100 the minimum is 7.5 ppm. That is a sign CYA is too high, not a reason to keep chlorine there. See how to lower CYA.

What destroys chlorine in a pool?

• Sunlight. UV breaks down unprotected chlorine fast. Stabilizer (CYA) shields it, which is why outdoor pools use it.
• Swimmers. Sweat, urine, sunscreen, and body oils all use up chlorine and form combined chlorine (chloramines).
• Debris and algae. Leaves, pollen, dirt, and early algae use up chlorine before you can see them.
• Heat and rain. Warm water speeds up every reaction. Heavy rain dilutes the pool and washes in dirt.

If chlorine is gone overnight, or drops much faster than usual with CYA in range, check why chlorine won't hold.

How to raise chlorine quickly

Use liquid chlorine or bleach: they are already dissolved and start working as soon as they mix. Pour the dose in front of a return jet with the pump running, and retest after 30 minutes. For 1,000 gallons, 1.28 fl oz of 10% liquid chlorine raises FC by 1 ppm. The liquid chlorine calculator sizes it for your pool, and how much chlorine to add covers bleach, tablets, and powders. Tablets are the slow option: they are made to dissolve over days.

When not to swim (above 10 ppm)

Stay out of the water when:

• FC is above 10 ppm, the upper limit in the CDC model code;
• FC is above the swimming limit on your product label (often 4 ppm);
• FC is below the minimum for your CYA, because the water is not reliably sanitized;
• you just shocked the pool and FC has not yet come back down to your label's limit.

High chlorine comes down on its own with sun and time. See what to do when chlorine is too high. If your test shows a gap between total and free chlorine, read free vs total chlorine: that gap is combined chlorine, and it needs a shock, dosed by your product's label. Every other target (pH, alkalinity, calcium, salt) is on the pool chemical chart.

Details for pool technicians

• Minimum = max(floor, k × CYA), rounded up to the next 0.5 ppm; k = 0.075 for manual chlorine, 0.05 for salt water generators; floor = 2 ppm with CYA, 1 ppm without.
• Target = from the minimum (at least 2 ppm) to 2 ppm above it, at least 4 and at most 10 ppm.
• HOCl estimate at pH 7.5, 77 °F: FC 3 with CYA 40 gives about 0.029 ppm. The model and the MAHC comparison are on the methodology page.

FAQ

What is the ideal FC to CYA ratio for a pool?

For manual chlorine, keep FC at or above 7.5% of CYA (for example, 3 ppm at CYA 40). For a salt water generator, about 5%. These follow the FC/CYA principle described in the MAHC Annex. The exact percentages come from pool-owner practice and are our parameterization.

What should my cyanuric acid level be?

30–50 ppm for pools chlorinated with liquid chlorine, bleach, or tablets. Use 30–40 ppm if you want your target to fit under a 4 ppm label limit. Salt water pools usually run 60–80 ppm; check your cell's manual. Hot tubs: none.

Is 80 CYA too high?

For a manually chlorinated pool, yes: it needs at least 6 ppm FC, above what swimming labels allow. For a salt pool it is the top of Hayward's range. Stabilizer leaves only with water: replacing half the water with fresh, stabilizer-free water takes 80 ppm to 40 ppm. See how to lower CYA.

Sources

• CDC, Model Aquatic Health Code 2024, Annex (5.7.3.1.1.2, CYA and hot tub guidance): cdc.gov (PDF)
• CDC, Home pool and hot tub water treatment and testing: cdc.gov
• PHTA fact sheet, Sodium hypochlorite: phta.org
• Hayward, AquaRite manual (stabilizer for salt pools): PDF
• EPA label, Clorox Regular Bleach, Reg. No. 5813-1 (2011): epa.gov (PDF)
• Secondary: FC/CYA ratio summary: poolchemtracker.com