Pool Construction
Pool Shock Calculator
Combined chlorine is high, water's hazy, or it just rained. Time to shock. How much depends on your shock type and pool volume — here's the math.
FAQ
Cal-hypo vs dichlor vs liquid? +
Cal-hypo is cheap and strong but raises calcium hardness. Dichlor is convenient but adds CYA every dose. Liquid chlorine is the pro choice — pure sodium hypochlorite, no side effects, predictable strength.
What is SLAM? +
Shock Level And Maintain. From TFP (Trouble Free Pool) — you keep free chlorine at a multiple of your CYA until water is clear and CC is below 0.5. Standard SLAM ratio: FC = CYA × 0.4.
Brush after shock? +
Yes — especially in algae. Algae cells hide in pores; brushing exposes them to chlorine. Run pump 24 hours minimum.
When to retest? +
Wait at least 30 min after circulating before testing free chlorine.