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How to lower chlorine in your pool

Figures checked 11/9/2026

Stop adding chlorine, keep everyone out, let it fall, and retest. Swim only once free chlorine is at or below the level on your product's label: most labels we checked say 4 ppm, and one tablet label says 3 ppm.

When chlorine is too high to swim

Chlorine labels set the level. A liquid chlorine label says SWIMMING POOL WATER DISINFECTION – Do not reenter pool with a chlorine level above 4 ppm for risk of bodily harm. A cal-hypo label says Reentry into treated swimming pool is prohibited above levels of 4 ppm chlorine due to risk of bodily injury. A trichlor tablet label is stricter: Re-entry into treated swimming pools/spas is prohibited above levels of 3.0 ppm. It also says Do not enter pool until the chlorine residual drops to 2.0 ppm (parts per million). CDC's model code for public pools defers to the label: Maximum DPD-FC concentrations shall not exceed limits specified on the product label.

The chlorine calculator and the all-in-one calculator say "Do not swim yet" whenever free chlorine is above 4 ppm, and never aim higher. The shock calculator goes higher on purpose, and tells you to keep everyone out until free chlorine is back down.

Readings above the test's limit

If your reading is very high, it may not be right. CDC says If the chlorine concentration of the water sampled from the pool or hot tub is more than 10 ppm, the test might partially or totally bleach out, resulting in a false low or 0 ppm chlorine result. So the calculators send readings above 10 ppm to a pool professional instead of giving an amount.

Chlorine neutralizers

We don't give a neutralizer amount: they aren't among the products our charts cover, and sources differ. If you use one, follow its label, and add nothing else at the same time.

What to do

  1. Stop adding chlorine.
  2. Keep everyone out of the pool.
  3. Let the chlorine fall.
  4. Retest free chlorine, and keep retesting until it is at or below your label's level.
  5. If you have tested combined chlorine and it is above 0.4 ppm, retest it once free chlorine is back down, then use the shock calculator if it is still high.

Questions people ask

How do I lower the chlorine in my pool?

Stop adding chlorine, keep everyone out, let it fall and retest until free chlorine is at or below your label's level. We don't give a neutralizer amount; if you use one, follow its label.

How long until I can swim again?

There's no set time: it is when free chlorine is at or below the level on your product's label, so retest. Most labels we checked say 4 ppm.

Is high chlorine a problem?

Above your label's level, yes: one label we checked says SWIMMING POOL WATER DISINFECTION – Do not reenter pool with a chlorine level above 4 ppm for risk of bodily harm.

Why does my test show very high or zero chlorine?

CDC says If the chlorine concentration of the water sampled from the pool or hot tub is more than 10 ppm, the test might partially or totally bleach out, resulting in a false low or 0 ppm chlorine result. If you suspect that, ask a pool professional (for example a pool store water test).

The charts behind this page

Show all 3 figures and where each one comes from

Each figure this page and its calculator use. Open one for the source's own words, the other sources we checked it against, and the checks it has been through.

  • Free chlorine above which chlorine labels say do not swim (re-entry level): 4 ppm Other source

    EPA-accepted label: B's Pool Supply Sodium Hypochlorite Solution 12.5% (EPA Reg. 55487-20001) Other source says: SWIMMING POOL WATER DISINFECTION – Do not reenter pool with a chlorine level above 4 ppm for risk of bodily harm. Source page (opens in a new browser tab)

    Also checked: EPA-accepted label: BioGuard Master Calcium Hypochlorite 67% (Bio-Lab, EPA Reg. 5185-238) Other source says: Reentry into treated swimming pool is prohibited above levels of 4 ppm chlorine due to risk of bodily injury. Source page (opens in a new browser tab)

    Also checked: EPA-accepted label: PDQ ChlorSan 8% Sodium Hypochlorite (EPA Reg. 58880-2) Other source says: Reentry into treated pools is prohibited above levels of 4.0 ppm due to risk of bodily harm. Source page (opens in a new browser tab)

    Also checked: HTH Pool Care Shock product page Other source says: Do not enter the pool until free available chlorine levels return to 1–4 ppm. Source page (opens in a new browser tab)

    Also checked: EPA-accepted label: Tarry trichlor 8 oz tablets/sticks (Qualco, EPA Reg. 3525-120) Other source says: Re-entry into treated swimming pools/spas is prohibited above levels of 3.0 ppm. Source page (opens in a new browser tab)

    Also checked: EPA-accepted label: Tarry trichlor 8 oz tablets/sticks (Qualco, EPA Reg. 3525-120) Other source says: Do not enter pool until the chlorine residual drops to 2.0 ppm (parts per million). Source page (opens in a new browser tab)

    Also checked: CDC Model Aquatic Health Code, 5th edition (2024), Code Official says: Maximum DPD-FC concentrations shall not exceed limits specified on the product label. Source page (opens in a new browser tab)

    Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.

  • Free chlorine reading above which the test may bleach out (false low): 10 ppm Official

    CDC: Home pool and hot tub water treatment and testing Official says: If the chlorine concentration of the water sampled from the pool or hot tub is more than 10 ppm, the test might partially or totally bleach out, resulting in a false low or 0 ppm chlorine result. Source page (opens in a new browser tab)

    Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure.

  • Combined chlorine level that calls for action (shock / superchlorinate): 0.4 ppm Official

    CDC Model Aquatic Health Code, 5th edition (2024), Code Official says: reduce the concentration of COMBINED CHLORINE (chloramines) in the water when the concentration exceeds 0.4 ppm (mg/L). Source page (opens in a new browser tab)

    Also checked: Oregon Health Authority: Water Quality Standards, OAR 333-062-1000 (public pools) Official says: Combined Chlorine 0ppm 0ppm 0.4ppm Source page (opens in a new browser tab)

    Also checked: Multnomah County (Oregon) Environmental Health: Water Treatment - Swimming Pools, EHS-0058 Official says: Breakpoint chlorinate when combined chlorine exceeds 0.5 ppm, or when chloramines are first detected. Source page (opens in a new browser tab)

    Checked against the source on 11/9/2026. Re-opened by a second checker on 11/9/2026, who matched the source's words to this figure. Looked up again on 11/10/2026 by a checker who couldn't see our figure: it came back with the same figure.