How much chlorine do I add?
Every chlorine product is rated by how much available chlorine it delivers. The amount you need is the ppm rise you want, times your pool's volume, divided by the product's strength:
amount = ppm rise x gallons x factor / strength %
For liquids the factor is 0.0001 (gallons of product), and for solids it is 0.000834 (pounds of product). Worked example, 15,000 gallons going from 1 to 4 ppm (a 3 ppm rise):
- 12.5% liquid chlorine: 3 x 15,000 x 0.0001 / 12.5 = 0.36 gal (46 fl oz)
- 8.25% bleach: 0.55 gal (70 fl oz)
- 65% cal-hypo: 3 x 15,000 x 0.000834 / 65 = 0.58 lb (9 oz)
- 56% dichlor: 0.67 lb (11 oz), adding about 2.7 ppm CYA
Chlorine and CYA: why 3 ppm isn't always enough
Cyanuric acid (stabilizer) shields chlorine from sunlight, but it also binds most of it. The more CYA in the water, the more free chlorine you need for the same sanitizing power. That is why this pool chlorine calculator asks for CYA first.
| CYA | Minimum FC | Target FC | Shock / SLAM FC |
|---|---|---|---|
| 20 ppm | 1.5 | 2.5 | 10 |
| 30 ppm | 2.5 | 3.5 | 12 |
| 40 ppm | 3 | 4.5 | 16 |
| 50 ppm | 4 | 6 | 20 |
| 60 ppm | 4.5 | 7 | 24 |
| 70 ppm | 5.5 | 8 | 28 |
| 80 ppm | 6 | 9 | 32 |
| 90 ppm | 7 | 10.5 | 36 |
CYA too high? The CYA calculator works out how much to drain. Full targets for every reading are on the ideal pool chemistry levels chart.
Liquid chlorine dosage chart
| Pool size | +1 ppm (12.5%) | +5 ppm (12.5%) | Shock 10 ppm (12.5%) | +1 ppm (10%) | Shock 10 ppm (10%) |
|---|---|---|---|---|---|
| 5,000 gal | 5 fl oz | 26 fl oz | 0.40 gal | 6 fl oz | 0.50 gal |
| 10,000 gal | 10 fl oz | 51 fl oz | 0.80 gal | 13 fl oz | 1.00 gal |
| 15,000 gal | 15 fl oz | 77 fl oz | 1.20 gal | 19 fl oz | 1.50 gal |
| 20,000 gal | 20 fl oz | 102 fl oz | 1.60 gal | 26 fl oz | 2.00 gal |
| 25,000 gal | 26 fl oz | 128 fl oz | 2.00 gal | 32 fl oz | 2.50 gal |
| 30,000 gal | 31 fl oz | 154 fl oz | 2.40 gal | 38 fl oz | 3.00 gal |
Metric: in 10,000 L, 80 mL of 12.5% (or 100 mL of 10%) raises FC by 1 ppm, and 0.8 L of 12.5% shocks to 10 ppm.
How much chlorine to shock a pool
Pick the shock level by why you are shocking and by your CYA:
- Routine or after a party: about 10 ppm, or 25% of CYA if higher.
- Cloudy water: about 30% of CYA, at least 10 ppm.
- Opening, green water or algae: SLAM at 40% of CYA, held until the water passes the overnight loss test.
- Chlorine smell (combined chlorine): about 10x the CC reading, at least 10 ppm.
For a 10 ppm shock with 12.5% liquid chlorine: 3,000 gallons needs about 0.24 gal (31 fl oz), 10,000 gallons about 0.8 gal, and 20,000 gallons about 1.6 gal. Green pool? Use the green pool recovery plan with its SLAM calculator and printable log, or the pool shock cheat sheet.
Liquid vs cal-hypo vs trichlor vs dichlor
| Product | Cost per ppm | Side effects | Best use |
|---|---|---|---|
| Liquid chlorine (10 to 12.5%) | Lowest | None (raises pH a little, briefly) | Daily dosing and SLAM |
| Bleach (6 to 8.25%) | Low | None if unscented | Small pools, top-ups |
| Cal-hypo (48 to 73%) | Medium | Adds about 0.7 ppm CH per 1 ppm FC | Occasional shock in soft water |
| Dichlor (56%) | Higher | Adds about 0.9 ppm CYA per 1 ppm FC | Spas, quick small doses |
| Trichlor tabs (90%) | Medium | Adds about 0.6 ppm CYA per 1 ppm FC, lowers pH | Steady feed in a chlorinator |
| Lithium hypo (35%) | Highest | None | Vinyl pools, no residue |
Salt pool? Your cell makes the chlorine; see the salt calculator and saltwater pool care. Learn the terms: free vs combined chlorine and chlorine lock.