How Much Liquid Chlorine to Add to Your Pool (With Dosing Charts)
If you've ever stood next to a jug of liquid chlorine wondering 'is one cup enough?' — this is the guide. Skip the back-of-the-envelope math, use the tables below, and get your free chlorine where it needs to be on the first pour.
TL;DR — the quick answer
To raise free chlorine (FC) by 1 ppm in 10,000 gallons, add roughly 11 fl oz (0.85 cups) of 12.5% liquid chlorine — or 22 fl oz of household 6% bleach. Pour into the deep end with the pump running, in the evening, and retest after an hour of circulation.
If that's all you needed, you can stop here. If you want the tables for larger pools, the shock math, or the reasoning — keep going.
What "liquid chlorine" actually is
Liquid chlorine is sodium hypochlorite — the same active ingredient as household bleach, just stronger. Pool-grade liquid chlorine is usually sold at 10% or 12.5% available chlorine, versus ~6% for standard laundry bleach. The percentage matters a lot for dosing: a gallon of 12.5% LC does roughly twice the work of a gallon of 6% bleach.
Three things to know before you pour:
- Strength decays over time. Liquid chlorine loses a few percent strength per month, faster in heat and sunlight. Buy fresh; don't stockpile for the season.
- It's unstabilized. Unlike tabs (trichlor) or shock powder (cal-hypo or dichlor), liquid chlorine adds no cyanuric acid (CYA) and no calcium. That's usually a feature, not a bug — it means you can dose aggressively without your stabilizer or hardness creeping up all season.
- It temporarily raises pH. Sodium hypochlorite is basic, so a big dose will push pH up a few tenths. It settles back as the chlorine is consumed.
Dosing chart: how much LC per 1 ppm of FC
This is the table you actually want. Figures are for 12.5% liquid chlorine, the most common pool-store strength. For 10% LC, multiply by 1.25. For 6% household bleach, multiply by 2.
| Pool size | +1 ppm FC | +2 ppm FC | +4 ppm FC (mild top-up) |
|---|---|---|---|
| 5,000 gal | 5.5 fl oz | 11 fl oz | 22 fl oz (≈ 2¾ cups) |
| 10,000 gal | 11 fl oz | 22 fl oz | 44 fl oz (≈ 1.4 qt) |
| 15,000 gal | 16 fl oz | 32 fl oz | 64 fl oz (½ gal) |
| 20,000 gal | 22 fl oz | 44 fl oz | 88 fl oz (≈ 2.75 qt) |
| 25,000 gal | 27 fl oz | 54 fl oz | 108 fl oz (≈ 3.4 qt) |
| 30,000 gal | 33 fl oz | 66 fl oz | 132 fl oz (≈ 1 gal) |
The formula, if you like math
For any strength of liquid chlorine, fluid ounces needed is:
fl oz = (ppm needed) × (gallons / 1000) × (12.5 / strength%)
Example: you have a 16,000-gallon pool, current FC is 1 ppm, target is 4 ppm, and you're using 10% LC.
- ppm needed = 4 − 1 = 3
- gallons factor = 16,000 / 1,000 = 16
- strength factor = 12.5 / 10 = 1.25
- fl oz = 3 × 16 × 1.25 = 60 fl oz ≈ half a gallon
If you'd rather not do this by hand, PoolTrack's dosing calculator does it for you — including a CYA-aware FC target.
What FC should you actually target?
The answer depends on your cyanuric acid (CYA), which acts as a UV sunscreen for chlorine. Higher CYA means you need more free chlorine to have the same sanitizing power. This is the relationship the Trouble Free Pool (TFP) method is built around, and it's the single most important concept in backyard pool chemistry.
| CYA (ppm) | Minimum FC | Target FC | Shock FC |
|---|---|---|---|
| 30 | 2 ppm | 4–6 ppm | 12 ppm |
| 40 | 3 ppm | 5–7 ppm | 16 ppm |
| 50 | 4 ppm | 6–8 ppm | 20 ppm |
| 60 | 5 ppm | 7–9 ppm | 24 ppm |
| 70 | 5 ppm | 8–10 ppm | 28 ppm |
| 80 (salt pool) | 6 ppm | 9–11 ppm | 31 ppm |
The takeaway: don't blindly aim for "3 ppm." A pool with CYA 70 and FC 3 is on the edge of an algae bloom even though strips say "ideal."
How much to add when you're shocking
"Shocking" a pool means driving FC up to a level that breaks down chloramines and kills algae, and then holding it there until the water clears and chlorine loss overnight drops below 1 ppm.
Shock FC is roughly 40% of your CYA. So a pool with CYA 50 shocks at around FC 20.
Worked shock example
15,000-gallon pool, CYA 40, current FC 2 ppm, 12.5% LC:
- Shock target: 40 × 0.4 = 16 ppm
- Bump needed: 16 − 2 = 14 ppm
- Dose: 14 × 15 = 210 fl oz — about 1.65 gallons of 12.5% LC
You won't hold shock level on a single pour; chlorine burns off as it kills organics. Expect to re-dose to shock 2–4 times a day for 1–3 days for a fresh algae bloom. This is why liquid chlorine, not tabs, is the shock weapon of choice — you'd spike CYA to useless levels trying to shock with trichlor.
When and how to add it
- Evening is best. UV destroys 2–4 ppm of FC per hour in a stabilized pool and faster in an unstabilized one. Dosing at dusk gets you a full night of sanitation before the sun starts eating it.
- Pump on. Pour while the pump is running so the water mixes instead of pooling on the plaster.
- Pour low and slow into the deep end. Walking around the edge with the jug spreads it, but the deep-end pour is plenty if your circulation is decent.
- Wait before retesting. Give it one full turnover (usually 1–6 hours depending on pump size) before you take the reading.
- Never swim for at least 15–30 minutes after a routine dose, or until FC is back below ~10 ppm after a shock dose.
Liquid chlorine vs tabs vs powder
| Form | Adds CYA? | Adds calcium? | Best for |
|---|---|---|---|
| Liquid chlorine (sodium hypochlorite) | No | No | Daily dosing, shock, summer heat |
| Trichlor tabs | Yes (~6 ppm per ppm FC) | No | Light maintenance in a floater; small pools; vacations |
| Cal-hypo powder | No | Yes | Vinyl/fiberglass pools where CH is already low |
| Dichlor powder | Yes | No | Spas, very small pools, travel |
For most chlorine pools: liquid is the workhorse, with tabs as a supplement when you're away. For salt pools: the salt cell is your liquid-chlorine generator — you top up with LC when demand spikes (parties, storms, heat waves).
FAQ
Can I use regular household bleach?
Yes. Unscented, plain bleach (sodium hypochlorite) is chemically identical — just weaker. Check the label for "6% sodium hypochlorite" and double the dose versus 12.5% pool-grade LC. Avoid anything labelled "splash-less," "scented," or "with cleaner" — the additives don't belong in your pool.
How long does liquid chlorine last in storage?
About 3–6 months at typical garage temperatures. It loses ~1% strength per month at 70°F, much faster in a hot Texas summer. Buy what you'll use in 4–6 weeks, store in the shade, and expect a half-strength jug by next spring if it oversummers.
Do I need to brush after adding chlorine?
Not for routine doses. After a shock, brushing the walls a few times over the shock period helps dislodge biofilm and dead algae so the chlorine can finish the job.
Why didn't my FC go up as much as the calculator said?
Three usual suspects: (1) your LC is older than the label claims, (2) you have significant chlorine demand (algae, ammonia, heavy organics) eating the dose, or (3) your test kit is reading low because FC is actually above its bleach-out limit. A good drop-count FAS-DPD test kit clears this up.
Can I add too much?
Hard to overdose to the point of danger in an outdoor pool — UV and organics burn it off fast. But 15+ ppm is uncomfortable to swim in, and sustained very high FC can damage liners and soft goods. If you overshoot, just stop dosing and wait a day.
Stop guessing, start logging
The reason you're doing this math in the first place is because what you added yesterday affects what you need today. PoolTrack logs every reading and every treatment, predicts where your FC is heading, and calculates the exact dose for your pool profile — including CYA-aware FC targets and salt-pool adjustments.
Try the free dosing calculator →