The quick answer: 10% liquid chlorine raises free chlorine (FC) by about 1 ppm for every 12.8 fl oz added to 10,000 gallons of water. In metric, that is 100 mL per 10,000 litres. To raise FC from 2 to 6 ppm in a 10,000 gallon pool, add about 51 fl oz (0.4 gal) of 10% liquid chlorine. The calculator below works it out for your pool, product strength and target.
The tricky part isn't the multiplication. It's knowing what target to aim for, and that depends on your stabilizer level. Both are covered below.
Liquid chlorine dose chart (raise FC by 4 ppm)
The most common daily job is topping FC up by a few ppm. This table shows the amount needed to raise FC by 4 ppm, for example from 2 to 6.
| Pool size | 12.5% liquid chlorine | 10% liquid chlorine | 6% bleach |
|---|---|---|---|
| 5,000 gal | 20 fl oz | 26 fl oz (0.2 gal) | 41 fl oz |
| 10,000 gal | 41 fl oz | 51 fl oz (0.4 gal) | 83 fl oz |
| 15,000 gal | 61 fl oz | 77 fl oz (0.6 gal) | 124 fl oz |
| 20,000 gal | 82 fl oz | 102 fl oz (0.8 gal) | 165 fl oz |
| 25,000 gal | 102 fl oz | 128 fl oz (1 gal) | 206 fl oz |
| 30,000 gal | 123 fl oz | 154 fl oz (1.2 gal) | 248 fl oz |
Per 1 ppm in 10,000 gallons: 10.2 fl oz of 12.5%, 12.8 fl oz of 10%, 14.5 fl oz of 8.25% bleach, or 20.6 fl oz of 6% bleach. Per 1 ppm in 10,000 litres: 80 mL of 12.5%, 100 mL of 10%, or 161 mL of 6% bleach.
These use the usual label conventions: pool chlorine (10% and up) is sold by trade percent, household bleach (below 10%) by weight. If your jug says "sodium hypochlorite 12.5%" and lists "available chlorine 11.9%", it is about 14% stronger than 12.5% pool chlorine: enter the available chlorine figure in the app and choose "Active chlorine by weight".
The math scales linearly. Twice the water needs twice the chlorine, and twice the ppm needs twice the chlorine. For any other size, use the calculator above.
Step 1: Know your target (it depends on CYA)
Cyanuric acid (CYA, also called stabilizer or conditioner) protects chlorine from sunlight. It does this by holding most of the chlorine in a reserve form. The more CYA you have, the more FC you need for the same sanitizing power.
That is why one fixed number such as "keep chlorine at 1–3 ppm" fails so many pool owners. A pool with 80 ppm of CYA at 2 ppm FC is under-chlorinated and will grow algae.
The rule used by experienced pool owners (popularized by TroubleFreePool) is to treat FC as a percentage of CYA:
- Minimum FC is 7.5% of CYA. Never let it drop below this.
- Daily target: the minimum plus a 3 ppm cushion, so that one sunny day can't drag you below the minimum.
- Shock (SLAM) level is 40% of CYA. This is used to clear algae, not for daily dosing, and nobody swims during a SLAM.
| CYA (ppm) | Minimum FC | Daily target | Shock (SLAM) FC |
|---|---|---|---|
| 30 | 2.3 | 5.3 | 12 |
| 40 | 3 | 6 | 16 |
| 50 | 3.8 | 6.8 | 20 |
| 60 | 4.5 | 7.5 | 24 |
| 70 | 5.3 | 8.3 | 28 |
| 80 | 6 | 9 | 32 |
Salt water (SWG) pools add chlorine continuously, so they are usually run at higher CYA (about 70–80 ppm). Their FC targets follow the same idea. Our full FC/CYA chart explains the details.
Step 2: Test, then calculate
- Test FC (and ideally CYA and pH) with a reliable kit. A drop-based FAS-DPD chlorine test is much more precise than strips.
- Subtract your current FC from your target. That is the ppm you need to add.
- Multiply by the per-ppm amount for your strength and pool size, or let the calculator do it.
Example: a 15,000 gallon pool with CYA 40 reads FC 3. The target at CYA 40 is 6 ppm.
- You need 3 ppm.
- That is 58 fl oz of 10% (0.45 gal).
Step 3: Add it the right way
- Pump running. Pour slowly in front of a return jet, or walk it around the deep end.
- Never mix liquid chlorine with acid, or pour them into the pool at the same spot. Add one, let it circulate for at least 30 minutes, then add the other. Mixing them releases chlorine gas.
- Evening is best. Chlorine added at dusk isn't burned off by the sun before it does its job overnight.
- Retest after 30 minutes if you added a large dose.
- Before swimming: Swim when free chlorine is back within your normal range and at or below the re-entry level on your chlorine label (many labels say 4 ppm). Never swim during a SLAM or with free chlorine above 10 ppm. Your product label always comes first.
Liquid chlorine vs bleach vs everything else
Liquid chlorine and bleach are the same chemical, sodium hypochlorite, at different strengths.
- Pool stores sell 10% or 12.5%. Household bleach is usually 6% to 8.25%.
- Bleach works perfectly well if it is plain and unscented, with no "splash-less" thickeners or fragrance.
- The label strength is all the calculator needs.
Liquid chlorine adds almost nothing else to your water. Over its life it leaves a little salt behind and has close to a neutral overall effect on pH. That's why it's the default choice for manual chlorination. The alternatives each add something:
| Product | Adds per 1 ppm FC | Watch out for |
|---|---|---|
| Liquid chlorine / bleach | Nothing significant | Loses strength in storage |
| Cal-hypo (65–73%) | about 0.7 ppm calcium hardness | Calcium builds up, which raises scale risk |
| Dichlor (56–62%) | about 0.9 ppm CYA | CYA climbs fast |
| Trichlor tablets (90%) | about 0.6 ppm CYA, and lowers pH | CYA creeps up all season |
If your CYA is already in range, liquid chlorine is usually the cleanest way to add chlorine without side effects. See liquid chlorine vs tablets for a full comparison.
How much liquid chlorine per day?
There is no universal daily number. Your pool's chlorine use depends on:
- sun exposure
- water temperature
- swimmers
- debris
- your CYA level
A pool with too little CYA can lose most of its chlorine on one sunny afternoon.
Find your own number: test FC at dusk two days in a row without adding anything in between. The drop is your daily use. Dose that amount each evening, plus a small cushion, and you'll rarely fall below the minimum.
If you lose more than about 1 ppm overnight (when there is no sun), something is consuming chlorine, usually early algae. Read cloudy pool water and run the overnight chlorine loss test.
Common mistakes
- Using a fixed target that ignores CYA. This is the number one reason "my chlorine is fine but my pool is green".
- Old chlorine. Liquid chlorine loses strength in storage, faster in a hot garage. If doses stop "working", suspect the jug before the pool.
- Guessing the pool volume. Being 30% off on gallons means every dose is 30% off. Measure it once with the pool volume calculator.
- Adding a big dose at noon in full sun. Much of it is lost before nightfall.
- Mixing chemicals. Add one product at a time.
Do it in the app
The calculator on this page answers one question. Pool Calc answers it every time you test:
- Enter your readings on one screen.
- It picks the FC target from your CYA.
- It gives the dose for the product on your shelf, in gallons or litres.
- Your log shows how fast your pool uses chlorine, so tomorrow's dose is a better guess than today's.
One pool? Every feature, free. No account, no ads, and iCloud backup is included.
Safety
- Keep chemicals out of reach of children and pets, and keep them out of the water until it is back in range.
- Never mix chemicals. Never add acid and chlorine together: mixing them releases toxic chlorine gas.
- Add chemicals to water, never water to chemicals.
- Store chemicals sealed, cool and dry, apart from each other.
- Read and follow the product label. It always comes first.