Your shock level is 40% of your CYA, not a fixed number of bags. This calculator sets that target from your stabilizer, then converts the gap to your current free chlorine into an exact dose for the chemical you have.
Shock target 16 ppm — raise by 16.0 ppm
At 40 ppm CYA the SLAM shock level is 16 ppm free chlorine — that is 40% of your CYA. This is a level to hold, not a single dose: retest and re-dose until the water clears.
Liquid chlorine 10%
307.2 fl oz (2.4 gal) (9085 mL)
To reach 16 ppm from 0.0 ppm in 15,000 gallons. Adds nothing but chlorine and salt — the SLAM default.
Before you dose
This calculator gives you today's number. The app remembers your pool.
Shocking is one step in clearing a pool — pH, filtration, and holding the level all matter. Poolably saves your pool's volume and history, builds the full treatment plan in the right order, and reminds you when to retest — free on iPhone.
Get Poolably freeStabilizer holds most of your chlorine in reserve, so the more CYA your water carries, the higher the free chlorine has to climb to kill algae. That is why shocking is set as a percentage of CYA rather than a single bag: at 40 ppm CYA the shock level is 16 ppm, at 80 ppm it is 31 ppm. Test your CYA before you start — if you do not know your volume, run the volume calculator first, and if you need your maintenance dose instead of a shock, use the chlorine calculator. Green water already? The full process is in the green pool fix, and the chemistry of shock treatment covers each product in depth.