Pool Shock Calculator

Calculate exactly how much shock to add to your pool. Enter your pool volume, current chlorine and CYA levels, and select your shock product.

How Pool Shocking Works

Pool shocking — also called superchlorination or breakpoint chlorination — means raising your pool's chlorine level high enough to destroy chloramines, algae, and other contaminants that regular chlorination can't eliminate.

When to Shock Your Pool

  • Combined chlorine above 0.5 ppm — this means chloramines are present, causing that "chlorine smell" and eye irritation.
  • After heavy use — pool parties, heavy rain, or high bather loads introduce contaminants.
  • Algae growth — green, yellow, or black algae require shock treatment to kill.
  • Weekly maintenance — many pool professionals recommend a weekly shock to prevent problems.

Understanding Breakpoint Chlorination

The shock target is calculated as the higher of two values:

Shock Target = MAX(CYA × 0.4, Current Chlorine + 10)

The CYA × 0.4 factor represents the breakpoint chlorination threshold — the level at which free chlorine can effectively oxidize contaminants relative to your stabilizer level. The minimum 10 ppm boost ensures enough chlorine is added even when CYA is low.

Shock Product Types

  • Calcium Hypochlorite (Cal-Hypo) — the most popular shock product. Available in 65% and 73% concentrations. Fast-acting, unstabilized, and affordable. Slightly raises calcium hardness and pH.
  • Dichlor (56% Available Chlorine) — a stabilized shock that also adds cyanuric acid. Good for pools with low CYA, but avoid if CYA is already high.
  • Non-Chlorine Shock (Potassium Monopersulfate) — oxidizes contaminants without raising chlorine levels. Allows swimming within 15 minutes. Best for routine oxidation, not algae treatment.

Tips for Effective Shocking

  • Always shock at dusk or night. UV sunlight breaks down chlorine rapidly, reducing effectiveness.
  • Run your circulation pump for at least 8 hours after adding shock to distribute it evenly.
  • Pre-dissolve granular shock in a bucket of pool water before adding it to prevent bleaching your liner.
  • Wait until free chlorine drops below 5 ppm before swimming (test with a reliable kit).
  • Retest your water 24 hours after shocking to confirm levels have returned to normal.