Pool shock calculator
To clear green or cloudy water, chlorine has to be held at a shock level that depends on your stabiliser (CYA). One big dose is rarely enough: the steps below matter as much as the number.
What next
- Brush the walls and floor, and run the filter 24 hours a day.
- Test morning and evening. Top chlorine back up to each time, about for every 1 ppm.
- Clean or backwash the filter when the pressure rises.
- Done when the water is clear and chlorine drops 1 ppm or less overnight.
- Do not swim while chlorine is above the normal range.
Without a stabiliser test we assume 30 ppm. Test it: at higher CYA the shock level is higher.
iPhone app · December 2026
Let the app walk you through it
Lido Pool keeps the shock level for you, reminds you to retest, tells you when the water is safe to swim in, and says when draining is the better option.
