How Much Liquid Chlorine to Add to Your Pool — Calculator
Enter your pool volume, CYA, and current FC — the minimum FC is set automatically. Supports liquid chlorine (10%, 12.5%), cal-hypo, and trichlor.
Standard pools: minimum FC = CYA × 7.5%. Saltwater / SWG pools: CYA × 5%. Many pools keep FC a little above the minimum as a daily buffer.
This is the minimum FC for your current CYA level. Many pools maintain FC slightly above the minimum as a daily buffer, and the PoolChem Tracker app may adjust the recommended target based on your pool's conditions. Edit the field to dose to a higher target.
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Why liquid chlorine is the preferred choice
Liquid sodium hypochlorite (pool bleach) raises FC cleanly — it adds only chlorine and water. Cal-hypo adds calcium, which can cloud water if your calcium hardness is already high. Trichlor adds CYA with every dose, which gradually raises your FC minimum and can lock you into a high-CYA chemistry spiral.
For regular top-offs, liquid chlorine at 10% or 12.5% is the simplest and cheapest option over a season. Cal-hypo is useful if you prefer a granular product or if your calcium hardness is on the low side.
Add chlorine near a return jet
With the pump running, pour liquid chlorine near a return jet or around the perimeter of the pool — never in front of the skimmer, and never mixed with other chemicals. For granular products, pre-dissolve in a bucket of pool water before adding.
How the chlorine dose is calculated
All dose formulas work from the same principle: how many grams of available chlorine do you need to raise FC by the target amount, given your pool's water volume?
Concentrations used: Liquid 10% = 0.10 (density 1.074 g/mL), Liquid 12.5% = 0.125 (density 1.094 g/mL), Cal-Hypo 65% = 0.65, Cal-Hypo 73% = 0.73, Trichlor 90% = 0.90.
Worked example
A 15,000-gallon pool tests at FC 1.5 ppm. Target is 4.0 ppm — a rise of 2.5 ppm. Using 12.5% liquid chlorine:
2.5 × 15,000 × 3.785 ÷ 1,000 = 142 g of available chlorine needed. Divided by (1.094 density × 29.57 mL/fl oz × 0.125 concentration) = about 35 fl oz — a little over 1 quart. Add near a return jet with the pump running. Wait 30 minutes and retest before assuming the job is done.
How much liquid chlorine to add to a 10,000, 15,000, or 20,000-gallon pool
These estimates assume dosing from FC 2 ppm to a typical minimum target (CYA 50 → FC 4 ppm). Your numbers may differ — use the calculator above for an exact dose based on your current FC and CYA.
| Pool size | FC rise | 10% liquid chlorine | 12.5% liquid chlorine |
|---|---|---|---|
| 10,000 gal | +1 ppm | ~12 fl oz | ~9.5 fl oz |
| 10,000 gal | +2 ppm | ~24 fl oz (1½ pints) | ~19 fl oz |
| 15,000 gal | +1 ppm | ~18 fl oz | ~14 fl oz |
| 15,000 gal | +2 ppm | ~36 fl oz (1 qt + 4 oz) | ~28 fl oz |
| 20,000 gal | +1 ppm | ~24 fl oz (1½ pints) | ~19 fl oz |
| 20,000 gal | +2 ppm | ~48 fl oz (1½ quarts) | ~37 fl oz |
| 25,000 gal | +1 ppm | ~30 fl oz | ~23 fl oz |
| 25,000 gal | +2 ppm | ~60 fl oz (1 qt + 1 pt) | ~47 fl oz |
Frequently asked questions
How much liquid chlorine raises FC by 1 ppm?
It depends on your pool volume and chlorine concentration — both scale linearly, so a 15,000-gallon pool needs 50% more than a 10,000-gallon pool, and 10% chlorine requires more volume than 12.5% for the same FC rise. Enter your pool size, current FC, and target FC in the calculator above to get the exact fl oz for your situation.
Should I use liquid chlorine or cal-hypo?
Liquid chlorine (sodium hypochlorite) is the preferred choice for routine dosing — it adds only chlorine and water, no calcium, no CYA. Cal-hypo is a reasonable alternative if your calcium hardness is below 200 ppm. Avoid trichlor for regular top-offs: it adds CYA with every dose and gradually raises your minimum FC target over the season.
What FC level should I be targeting?
Enter your CYA in the calculator above and it sets your target FC automatically — CYA × 7.5% for standard pools, CYA × 5% for saltwater/SWG. At CYA 50, that's 3.5–4 ppm; at CYA 80, it's 6 ppm. See the FC/CYA chart for the full table by CYA level.
How often do I need to add chlorine?
Most pools need chlorine added every 2–4 days during swim season — daily during heat waves or heavy use. If FC drops more than 1–2 ppm per day without a clear cause, test your CYA level. Low CYA means sunlight is destroying chlorine faster than you're adding it.
Why does my pool chlorine drop so fast?
Fast FC loss usually has one of four causes: CYA too low (UV destroying unprotected chlorine), early algae growth consuming FC overnight, heavy bather load, or pH above 8.0 (reducing chlorine's effectiveness). Test CYA first — it's the most common culprit and the easiest to fix.