🧨 Cal-Hypo Shock (65–73%)
granular calcium hypochlorite, 65–73% available chlorine · updated August 2026
Quick answer: add 2 oz per 10,000 gallons to raise Free Chlorine 1 ppm. Ideal Free Chlorine: 1–3 ppm (shock: 10–12 ppm). Add ½–⅔ first, circulate, retest.
Safety — read first
- • NEVER let cal-hypo touch trichlor — mixing the two can ignite or explode.
- • Pre-dissolve in a bucket of water for vinyl-liner pools to avoid bleaching.
The standard granular shock. Strong, unstabilized chlorine — great for weekly shocking and algae kills where CYA is already sufficient.
Side effects: Adds ~0.7 ppm calcium hardness per 1 ppm FC — avoid if your CH is already high. Slightly raises pH.
Dosing chart
| Pool size | +1 ppm | +2 ppm | +5 ppm | +10 ppm |
|---|---|---|---|---|
| 5,000 gal | 1.0 oz | 2.0 oz | 5.0 oz | 10.0 oz |
| 10,000 gal | 2.0 oz | 4.0 oz | 10.0 oz | 1.3 lb |
| 15,000 gal | 3.0 oz | 6.0 oz | 15.0 oz | 1.9 lb |
| 20,000 gal | 4.0 oz | 8.0 oz | 1.3 lb | 2.5 lb |
| 30,000 gal | 6.0 oz | 12.0 oz | 1.9 lb | 3.8 lb |
Calculate your exact dose
1 · Your pool's volume
Working with 20,000 gallons
2 · What are you fixing?
Ideal Free Chlorine: 1–3 ppm (shock: 10–12 ppm). Adjusting pH? Doses aren't linear — see soda ash / muriatic acid.
3 · Add one of these
Slightly raises pH. Loses strength in storage — buy fresh, store cool and dark.
Adds ~0.7 ppm calcium hardness per 1 ppm FC — avoid if your CH is already high. Slightly raises pH.
Adds ~0.9 ppm CYA per 1 ppm FC — CYA builds up fast. Fine early season, switch to liquid or cal-hypo once CYA hits 30–50.
Adds ~0.6 ppm CYA per 1 ppm FC and is strongly acidic — expect pH and alkalinity to drift down with steady tab use.
Estimates from standard label dosing, to raise Free Chlorine by 2.5 ppm in 20,000 gallons. Add ½–⅔ of the dose first, circulate 4–6 hours, retest, then top up. Never mix chemicals with each other.
FAQ
How much cal-hypo shock do I add per 10,000 gallons?+
2 oz per 10,000 gallons will raise Free Chlorine 1 ppm. Scale linearly with your pool size — the chart on this page covers 5,000 to 30,000 gallons.
What does cal-hypo shock do to a pool?+
The standard granular shock. Strong, unstabilized chlorine — great for weekly shocking and algae kills where CYA is already sufficient. Side effect to know: Adds ~0.7 ppm calcium hardness per 1 ppm FC — avoid if your CH is already high. Slightly raises pH.
Is cal-hypo shock safe to handle?+
NEVER let cal-hypo touch trichlor — mixing the two can ignite or explode. Pre-dissolve in a bucket of water for vinyl-liner pools to avoid bleaching.