How to use this pool chlorine calculator
- Enter your pool volume.
- Test the current free chlorine level.
- Choose a target: 1–3 ppm is typical for normal operation; salt and CYA levels affect the ideal value.
- Pick the product and add it with the pump running, preferably in the evening.
Example
To raise a 20,000 gallon pool from 1 to 4 ppm of free chlorine with 12.5% liquid chlorine you need 61 fl oz (0.48 gal).
What to know before you buy
Types of chlorine
Liquid chlorine (sodium hypochlorite, 10–12.5%) adds nothing but chlorine and a little salt. Cal-hypo adds calcium, and dichlor and trichlor add cyanuric acid (stabilizer) with every dose. Choosing the right product depends on your water's calcium and CYA levels.
How much free chlorine to keep
A common guideline is to keep free chlorine at about 7.5% of your CYA level, with at least 1–3 ppm. Salt pools can run a bit lower. Test daily in summer, as sun and swimmers consume chlorine quickly.
12.5% liquid chlorine to raise free chlorine by 1 ppm
| Pool volume | Amount to add | Liters |
|---|---|---|
| 5,000 gal | 5 fl oz | 0.15 L |
| 10,000 gal | 10 fl oz | 0.3 L |
| 15,000 gal | 15 fl oz | 0.45 L |
| 20,000 gal | 20 fl oz | 0.61 L |
| 30,000 gal | 31 fl oz | 0.91 L |
Formula
Chlorine needed (g of available chlorine) = liters × ppm increase ÷ 1,000. Product amount = chlorine needed ÷ strength. For liquids, strength is grams of available chlorine per 100 mL (trade %).
Tips from the pros
- Pour liquid chlorine in front of a return jet with the pump running.
- Add chlorine in the evening; sunlight destroys unstabilized chlorine within hours.
- Keep the right free chlorine level for your cyanuric acid (CYA): more stabilizer requires more chlorine.
Common mistakes to avoid
- Mixing different chlorine products or chemicals together before adding them: this can be dangerous.
- Using old liquid chlorine: it loses strength over time, especially in heat.
Frequently asked questions
How much liquid chlorine to raise 1 ppm?
About 10 fl oz of 12.5% liquid chlorine raises 10,000 gallons by 1 ppm.
Is household bleach the same as pool chlorine?
It is the same chemical at lower strength. Use plain, unscented bleach without additives.
Is this for shocking the pool?
Yes, set the target to your shock level. The right shock level depends on your cyanuric acid (stabilizer) reading.
How much bleach do I need for my pool?
About 21 fl oz of 6% household bleach raises 10,000 gallons by 1 ppm of free chlorine.
How long after adding chlorine can I swim?
With liquid chlorine, typically after the pump has circulated for 30 minutes to an hour and free chlorine is within the normal range.