PooloraHow much chlorine to add to a pool
The short answer depends on three numbers: how much chlorine you need to add, how big your pool is, and how strong your bottle is. Here is the chart, the math and the safety limits.
- In 10,000 gallons, 10% liquid chlorine raises free chlorine by 1 ppm with about 13 fl oz (1.5 cups · 380 mL).
- In 10,000 litres, it takes 100 mL of 10% liquid chlorine (80 mL of 12.5%) to raise free chlorine by 1 ppm.
- How much chlorine your water needs depends on your stabilizer (CYA). More CYA, more chlorine.
- Your product label decides when you can swim, usually up to 3 or 4 ppm.
Dose chart per 10,000 gallons
Find how many ppm you need to raise (your target minus your reading) and read across. For 20,000 gallons double the amount; for 15,000 multiply by 1.5. The amounts are rounded to a measuring cup (¼ cup or ½ fl oz).
| Raise FC by | Liquid chlorine 10% | Liquid chlorine 12.5% | Bleach 6% | Bleach 8.25% |
|---|---|---|---|---|
| 1 ppm | 13 fl oz 380 mL | 10 fl oz 305 mL | 2.5 cups 615 mL | 15 fl oz 440 mL |
| 2 ppm | 3.25 cups 755 mL | 2.5 cups 605 mL | 5.25 cups 1.25 L | 3.75 cups 875 mL |
| 3 ppm | 4.75 cups 1.15 L | 3.75 cups 910 mL | 7.75 cups 1.85 L | 5.5 cups 1.3 L |
| 5 ppm | 8 cups 1.9 L | 6.5 cups 1.5 L | 13 cups 3.05 L | 9.25 cups 2.2 L |
Use plain, unscented bleach only. Scented, "splash-less" or thickened bleaches contain additives that do not belong in a pool.
Using chlorine powder or granules instead? See how much chlorine powder to add for cal-hypo and dichlor.
Dose chart per 10,000 litres
The same chart in metric. For 50,000 litres multiply by 5. Pool liquid chlorine in Australia and the UK is usually 10% or 12.5%.
| Raise FC by | Liquid chlorine 10% | Liquid chlorine 12.5% | Bleach 6% |
|---|---|---|---|
| 1 ppm | 100 mL | 80 mL | 160 mL |
| 2 ppm | 200 mL | 160 mL | 325 mL |
| 3 ppm | 300 mL | 240 mL | 485 mL |
| 5 ppm | 500 mL | 400 mL | 810 mL |
How much chlorine for your pool size
A typical top-up raises free chlorine by about 2 ppm, for example from 1 to 3 ppm. Here is that dose for common pool sizes. For other increases, use the charts above or the calculator.
In gallons (raise FC by 2 ppm)
| Pool size | Liquid chlorine 10% | Liquid chlorine 12.5% | Bleach 6% |
|---|---|---|---|
| 10,000 gal | 3.25 cups 755 mL | 2.5 cups 605 mL | 5.25 cups 1.25 L |
| 15,000 gal | 4.75 cups 1.15 L | 3.75 cups 910 mL | 7.75 cups 1.85 L |
| 20,000 gal | 6.5 cups 1.5 L | 5 cups 1.2 L | 10.25 cups 2.45 L |
| 25,000 gal | 8 cups 1.9 L | 6.5 cups 1.5 L | 13 cups 3.05 L |
| 30,000 gal | 9.5 cups 2.25 L | 7.75 cups 1.8 L | 15.5 cups 3.7 L |
In litres (raise FC by 2 ppm)
| Pool size | Liquid chlorine 10% | Liquid chlorine 12.5% |
|---|---|---|
| 20,000 L | 400 mL | 320 mL |
| 30,000 L | 600 mL | 480 mL |
| 40,000 L | 800 mL | 640 mL |
| 50,000 L | 1 L | 800 mL |
| 60,000 L | 1.2 L | 960 mL |
Not sure how many gallons or litres your pool holds? Work it out with the pool volume calculator.
What the percentage on the bottle means
Pool liquid chlorine is usually labeled in trade percent: grams of available chlorine per 100 mL. Household bleach is labeled as sodium hypochlorite by weight, which needs the liquid's density to convert. That is why 6% bleach is not exactly 60% as strong as 10% pool chlorine, and why Poolora asks which kind of bottle you have.
Strength also fades. Liquid chlorine slowly loses strength in storage, faster in heat and sun. If an old bottle seems to do less than the chart says, it probably is weaker than its label. Buy what you will use within the season and keep it in the shade.
How much chlorine your water needs: it depends on stabilizer
Stabilizer (cyanuric acid, CYA) protects chlorine from the sun, but it also holds on to part of it, so the more CYA you have, the more free chlorine you need for the same disinfecting power. This relationship has been known since the 1970s (O'Brien, 1974). The levels below are what Poolora uses:
| Stabilizer (CYA) | Minimum FC | Target FC range | Algae shock level (chemistry) |
|---|---|---|---|
| 0 ppm | 1 ppm | 1–3 ppm | 10 ppm |
| 20 ppm | 2 ppm | 3–5 ppm | 10 ppm |
| 30 ppm | 2.25 ppm | 4–6 ppm | 12 ppm |
| 40 ppm | 3 ppm | 5–7 ppm | 16 ppm |
| 50 ppm | 3.75 ppm | 6–8 ppm | 20 ppm |
| 60 ppm | 4.5 ppm | 7–9 ppm | 24 ppm |
| 70 ppm | 5.25 ppm | 8–10 ppm | 28 ppm |
| 80 ppm | 6 ppm | 9–11 ppm | 32 ppm |
Two rules sit on top of the chemistry. The CDC sets a floor of 1 ppm without stabilizer and 2 ppm with it. And your product label sets a ceiling for swimming (next section). The minimum is about 7.5% of your CYA, so with CYA 40 you need at least 3 ppm, and with CYA 80 at least 6 ppm.
When it is safe to swim: the label decides
Pool chlorine is an EPA-registered pesticide, and its label is the legal limit. The labels we checked say, for example, "Do not reenter pool until the chlorine residual is between 1.0 to 3.0 ppm" (a 10% product) and that re-entry "is prohibited above levels of 4 ppm" (a 12.5% product). Read yours: the range is printed in the directions for use.
This creates a quiet conflict with stabilizer. If your label allows up to 3 ppm, the chemistry minimum only fits under it while CYA is 40 ppm or less; with a 4 ppm label, up to about 53 ppm. Above that, no chlorine level is both legal for swimming and strong enough for the stabilizer. That is why Poolora keeps the default stabilizer target at 30–40 or 30–50 ppm depending on your label, and why it doses chlorine only up to the label maximum.
Green water and shock
Clearing algae takes a high, steady chlorine level (about 40% of your CYA) until the water is clear and chlorine holds overnight. But the labels we checked cap superchlorination at 5 to 10 ppm. Ten ppm is 40% of 25, so with stabilizer above 25 ppm the chemistry level is above what the label allows. In that case the honest fix is to lower stabilizer by replacing water first (see the stabilizer guide), then shock within the label limit. Nobody swims until chlorine is back inside the label's swimming range.
Worked example
A 15,000-gallon pool reads FC 1.5 ppm with stabilizer at 30 ppm. The chemistry target range for CYA 30 is 4–6 ppm, and the label on this bottle allows swimming up to 4 ppm, so the target is 4 ppm. The increase is 2.5 ppm × 15,000 gallons, and with 10% liquid chlorine that is 6 cups (48 fl oz · 1.4 L).
Pour it slowly in front of a return jet with the pump running, keep everyone out while you add it, let it circulate and retest. Then test again the next day: the drop overnight tells you how much chlorine your pool uses.
Do it safely
- Never mix chlorine with acid or any other chemical, not even in the same empty bucket.
- Add chlorine last, after any acid has circulated.
- Wear gloves and eye protection, and store chlorine away from acid, in the shade.
- Follow the dose limits and directions on your own label; this chart is an estimate.
Common questions
Is bleach the same as pool chlorine?
Yes, both are sodium hypochlorite. Bleach is just weaker, so you need more of it. Use plain, unscented bleach and check its percentage on the label.
How long after adding chlorine can I swim?
When a test shows free chlorine back inside the swimming range on your product label. There is no fixed number of minutes; it depends on how much you added and how fast your pool uses it.
Why does my chlorine drop to zero every day?
The usual causes are sunlight with too little stabilizer, algae that is not visible yet, or a very hot, busy pool. Check stabilizer first: with CYA at 30–40 ppm the sun burns much less chlorine.
Should I add the whole dose at once?
For a normal top-up, yes, poured slowly in front of a return with the pump running. For large doses, split it and retest in between so you do not overshoot the label limit.
How much chlorine per litre of pool water?
With 10% liquid chlorine, 100 mL for every 10,000 litres (10 m³) raises free chlorine by 1 ppm. With 12.5% liquid chlorine it takes 80 mL, and with 6% bleach about 160 mL, for the same 10,000 litres.
Do it with your own products
Poolora turns your test into the exact amount of the products on your shelf, in cups and ounces, in the right order, and tells you when it's safe to swim. Free to start; every chemical, water balance and history are part of Pro.
Keep going
Sources
- CDC: Home pool and hot tub water treatment and testing (1 ppm minimum, 2 ppm with stabilizer)
- U.S. EPA registered labels for sodium hypochlorite pool products (Reg. No. 70271-10 and 82357-1): swimming re-entry range and 5–10 ppm superchlorination
- O'Brien, J. E. et al. (1974), chlorine and cyanuric acid equilibria in water: the basis of the chlorine–stabilizer relationship
- Doses: mass balance from the Poolora engine (ppm × liters ÷ available chlorine per mL), checked in the app's unit tests