Pool Shock Calculator
Calculate exactly how much shock to add to your pool.
Shock dose reference table
| Pool volume | Cal-hypo 68% | Liquid chlorine 12.5% | Dichlor 56% |
|---|---|---|---|
| 10,000 gal | 1.2 lb | 0.62 gal | 1.5 lb |
| 15,000 gal | 1.8 lb | 0.93 gal | 2.3 lb |
| 20,000 gal | 2.5 lb | 1.24 gal | 3 lb |
| 25,000 gal | 3.1 lb | 1.54 gal | 3.8 lb |
| 30,000 gal | 3.7 lb | 1.85 gal | 4.5 lb |
Which shock should you choose?
Cal-hypo
Fast and effective for routine shocking and algae. It raises calcium hardness, so avoid repeated use when calcium is already high.
Liquid chlorine
A good choice when you want chlorine without adding CYA or calcium. Store it cool and use fresh product.
Dichlor
Convenient and stable, but every dose raises CYA. Use it sparingly when stabilizer is already elevated.
MPS (non-chlorine)
Useful as an oxidizer between chlorine treatments. It is not a replacement for chlorine when killing algae.
When should you shock?
Routine weekly shock
Raise FC to about 10 ppm, circulate thoroughly, and retest before swimming.
Light algae (green tint)
Raise FC to about 20 ppm, circulate thoroughly, and retest before swimming.
Heavy algae (dark green)
Raise FC to about 30 ppm, circulate thoroughly, and retest before swimming.
Cloudy water
Raise FC to about 12 ppm, circulate thoroughly, and retest before swimming.
After heavy rain
Raise FC to about 12 ppm, circulate thoroughly, and retest before swimming.
Pool opening
Raise FC to about 15 ppm, circulate thoroughly, and retest before swimming.
How to add shock
- Test free chlorine, CYA and pH.
- Adjust pH toward 7.2–7.6.
- Pre-dissolve only when the label says to; never mix products.
- Add the measured dose at dusk across the deep end.
- Run the pump for at least 8 hours.
- Retest FC the next morning.
Frequently asked questions
How much shock do I need for a 15,000 gallon pool?
Enter 15,000 gallons, your current FC and CYA above. The calculator adjusts the dose for the treatment scenario and product strength.
Can I swim after shocking my pool?
Wait until FC returns to 1–4 ppm, which usually takes 8–24 hours. Always follow your product label.
Can I add algaecide and shock at the same time?
No. Shock first, let the pump circulate, and wait 24 hours before adding algaecide.
Does shock raise CYA?
It depends on the product. Dichlor raises CYA; cal-hypo and liquid chlorine do not.
Can you add too much shock?
Yes. Measure carefully, avoid mixing products, and keep people out until FC is back in range.
Should I shock in winter?
Shock when water is warm enough for algae activity or when opening the pool. Follow your winterizing plan in cold water.