Pool Shock (Superchlorination / Breakpoint)

What it actually means in practice

Shocking a pool — also called superchlorination or breakpoint chlorination — means raising free chlorine to roughly 10 times the current combined chlorine reading. That concentration is high enough to oxidize nitrogen-containing compounds (urine, sweat, sunscreen residue) that have bonded with chlorine and produced chloramines. Under the breakpoint, chlorine just keeps adding to the chloramine pool; over it, the bonds break and combined chlorine drops. Commercial pools in heavy use typically shock weekly; after heavy bather-load events (pool parties, holiday weekends), shock same-day.

What people commonly get wrong

• Shocking doesn't fix chlorine lock. That's a different problem (high cyanuric acid).

• Running the pool closed after shock isn't just optional — chlorine above 5 ppm violates IDPH operating ranges.

• `Non-chlorine shock` (MPS / potassium monopersulfate) oxidizes but doesn't break chloramines; it's a complementary tool, not a replacement.