Exactly how much chlorine to add to hit your target — liquid, bleach, cal-hypo, dichlor, or trichlor. CYA-aware targets, a shock mode, and how often you’ll need to re-dose.
Pool type
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CYA shields chlorine from sunlight — essential outdoors. It also sets your correct chlorine target: higher CYA needs more chlorine. Ideal range 30–50 ppm. Learn more →
Fast-acting, adds no CYA or calcium; nudges pH up. The best all-round choice for dosing and shocking.
Add this much liquid chlorine
3.9 quarts (≈ 125 fl oz)
to raise from 0 to 6 ppm in 20,000 gal
1.3 × (vol ÷ 10,000) × ΔFC ÷ (avail% ÷ 100) → 1.3 × (20,000 ÷ 10,000) × 6.0 ÷ 0.125
1.3 oz per 10,000 gal raises free chlorine 1 ppm (Indiana DOH / NSPF). Liquids → fluid ounces, solids → weight ounces.
Chlorine is used up every day by sunlight, swimmers, and debris, so a single dose doesn’t last — topping up is a daily-to-weekly job. The default burn-off rate is driven by your stabilizer (CYA) — more CYA means chlorine lasts longer. It’s an estimate — adjust it to match your pool.
CDC recommends at least 1 ppm free chlorine (2 ppm if using CYA), and pH 7.0–7.8. For outdoor pools the right target rises with your cyanuric acid:
| CYA (ppm) | Minimum FC | Target FC |
|---|---|---|
| 30 | 2 | 4–6 |
| 40 | 3 | 5–7 |
| 50 | 4 | 6–8 |
| 60 | 5 | 7–9 |
| 70 | 5 | 8–10 |
| 80 | 6 | 9–11 |
Saltwater pools run higher CYA (60–80 ppm). Indoor pools and hot tubs don’t use CYA — keep 1–4 ppm (pools) or 3 ppm+ (hot tubs).
Liquid chlorine and cal-hypo add no stabilizer, so they’re the safest for everyday dosing and shocking. Trichlor tablets and dichlor are “stabilized” — they add cyanuric acid (CYA) every time you use them. Handy in moderation, but they raise CYA all season, and once it climbs too high your chlorine stops working well.
| Product | Adds to water | pH |
|---|---|---|
| Liquid chlorine (sodium hypochlorite) | Nothing extra | Raises |
| Household bleach | Nothing extra | Raises |
| Cal-hypo (calcium hypochlorite) | Calcium hardness | Raises |
| Dichlor (stabilized granular) | Cyanuric acid (~0.9 ppm CYA per 1 ppm FC) | Lowers |
| Trichlor (stabilized tablets) | Cyanuric acid (~0.6 ppm CYA per 1 ppm FC) | Lowers |
The calculator flags the CYA a stabilized product adds — both per dose and per month if you maintain with it — so you can see your stabilizer climbing before it becomes a problem.
Enter your pool volume, current free chlorine, and target, then pick your product — the calculator multiplies 1.3 oz per 10,000 gallons per 1 ppm and divides by the product’s available-chlorine strength. As a rough guide, about 10–11 fl oz of 12.5% liquid chlorine raises a 10,000-gallon pool by 1 ppm.
Roughly 10.7 fl oz of 12% sodium hypochlorite (liquid chlorine) raises free chlorine by 1 ppm in 10,000 gallons. Stronger 12.5% liquid needs a touch less; weaker 10% needs a bit more. The calculator scales this exactly to your volume and target.
Household bleach is the same chemical (sodium hypochlorite) but weaker — usually 6–8.25% versus 10–12.5% for pool liquid chlorine — so you need more of it. Select “Household bleach” and its strength and the calculator adjusts the amount. Use plain, unscented bleach only.
UV sunlight destroys unprotected free chlorine fast — about half within 17 minutes of direct sun, and 50–90% within a few hours. Cyanuric acid (CYA / stabilizer) shields chlorine from UV so it lasts 3–5× longer. For any outdoor pool, keep CYA around 30–50 ppm; without it you’ll never hold a chlorine level through the afternoon.
Chlorine is consumed continuously by sunlight, swimmers, and debris — a typical stabilized outdoor pool loses about 2–4 ppm of free chlorine per day. That makes chlorine a recurring task: most pools need topping up every day or two, or a larger dose two to three times a week. The calculator’s “Keeping it there” panel estimates your daily loss and the maintenance dose to hold your target.
Yes. Trichlor tablets and dichlor granules are “stabilized” — they dissolve cyanuric acid (CYA) into the water along with chlorine. Trichlor adds about 0.6 ppm CYA for every 1 ppm of free chlorine it delivers (dichlor about 0.9), so steady tablet use can push CYA up 40+ ppm over a summer. Because CYA only leaves by draining and refilling, it builds up — and once it passes roughly 50–80 ppm your chlorine turns sluggish (“over-stabilization”). If you rely on tablets, test CYA regularly and switch to liquid chlorine or cal-hypo (which add no CYA) when it climbs. This calculator shows how much CYA your chosen product adds, per dose and per month.
Normal dosing keeps free chlorine in its everyday range. Shocking raises it sharply to burn off chloramines (the “chlorine smell,” from combined chlorine) or to kill algae. Breakpoint for chloramines is about 10× the combined chlorine level; algae cleanup runs around 40% of your CYA. Always shock with unstabilized chlorine (liquid or cal-hypo), never tablets.
How many gallons (or liters) your pool holds — any shape, sloped depths, spas included. The number you need before dosing anything.
Open toolDial in cyanuric acid and the ideal FC/CYA ratio so your chlorine actually works.
Open toolHow much salt to add to reach your salt-chlorine generator’s target level.
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