Do not guess at chlorine dosing. The formula:
Pounds of chlorine needed = (Target ppm − Current ppm) × Pool gallons ÷ 1,000,000 ÷ (Active chlorine % ÷ 100)
This looks complex but simplifies nicely. The practical approach: use the reference table below and interpolate for your pool size.
| Product | 10,000 gal | 20,000 gal | 30,000 gal |
|---|---|---|---|
| Calcium hypochlorite 65% (granular) | 1.3 oz | 2.6 oz | 3.9 oz |
| Sodium hypochlorite 10% (liquid) | 11 oz | 22 oz | 33 oz |
| Household bleach 6% (sodium hypochlorite) | 18 oz | 36 oz | 54 oz |
| Trichlor tablets 90% | 0.9 oz | 1.8 oz | 2.7 oz |
To raise chlorine by 2 ppm, double these amounts. To raise by 5 ppm, multiply by 5.
| Pool Size | Calcium Hypochlorite (65%) | Liquid Chlorine (10%) |
|---|---|---|
| 10,000 gallons | 1 lb (bag) | 110 oz (~1 gallon) |
| 15,000 gallons | 1.5 lbs | 165 oz |
| 20,000 gallons | 2 lbs | 220 oz (~1.7 gallons) |
| 30,000 gallons | 3 lbs | 330 oz (~2.6 gallons) |
Trichlor tablets (3-inch) are slow-dissolving and are designed for ongoing maintenance, not shock dosing. A general starting point is one tablet per 5,000 gallons per week. A 20,000-gallon pool typically needs 3–4 tablets per week in the floater or automatic feeder.
However, tablets also contain cyanuric acid (CYA), which builds up over the season. If CYA climbs above 80 ppm, partial drain and refill is needed. Some pool pros prefer liquid chlorine to avoid CYA accumulation.
Know your pool volume before dosing anything. If you do not know your pool size, calculate it: length × width × average depth × 7.48 (rectangular pool). Round pools: diameter² × depth × 5.9.
You may need more chlorine than the baseline if:
Never add chlorine based on a schedule alone. Always test free chlorine first. A pool sitting idle in cool weather for a few days may still have 2 ppm and need nothing. The same pool after a hot weekend with 10 swimmers may have dropped to zero and need immediate attention.
Enter your pool volume, current reading, and target level — SplashLens calculates the exact dose in ounces or pounds. No math required.
Open SplashLens Free →Start with one 3-inch tablet per 5,000 gallons per week, then adjust based on actual test results. A 20,000-gallon pool typically uses 3–4 tablets per week, but temperature, sun, and swimmer load all affect the rate.
Yes. Free chlorine above 5 ppm is not safe for swimming. Above 10 ppm can irritate eyes, skin, and airways. If you overdose, stop adding chlorine, run the pump, and let sunlight reduce the level naturally over 24–48 hours.
Granular calcium hypochlorite is 65–73% active chlorine and raises calcium hardness over time. Liquid sodium hypochlorite is 10–12.5% and does not affect calcium but slightly raises pH. Both work well; granular is preferred for shocking.
To raise free chlorine by 1 ppm in 10,000 gallons, add about 11 oz of 10% sodium hypochlorite. Regular household bleach at 6% requires about 18 oz for the same effect. Scale up proportionally for larger pools.
Only if testing shows free chlorine is below 1 ppm. Most pools need chlorine added every 2–3 days in summer. Chlorine tablets in a floater provide slow continuous release. Daily testing during peak season will show your pool's specific consumption rate.