Fast unstabilised chlorine shock for pools and indoor spas. 65% calcium hypochlorite granules deliver a 5-10 ppm chlorine kick in minutes, with no cyanuric acid build-up.
Standard dose adds 1 ppm. For a 5 ppm shock multiply by 5; for a 10 ppm super-chlorination multiply by 10. Always pre-dissolve.
Calcium hypochlorite (Ca(OCl)2), supplied as fast-dissolving granules with at least 65% available chlorine. Free of cyanuric acid stabiliser.
Calcium hypochlorite dissolves to release hypochlorous acid and calcium ions. The hypochlorous acid is the active sanitiser and oxidiser; the calcium fraction adds about 7 ppm hardness per 5 g per 1000 L. Without CYA, the chlorine is fully active in indoor and high-CYA outdoor settings.
Stabilised chlorine builds CYA over time and loses kill power above 50 ppm CYA. Calcium hypochlorite is the standard professional reset: it kills, oxidises and does not raise CYA, returning the system to chlorine-effective conditions in one shock.
Approximately 7.5 g per 1000 L of water, pre-dissolved in 10 L of warm water before adding.
Yes. Each 1 ppm of chlorine added with calcium hypochlorite lifts pH by about 0.05 units.
Wait until free chlorine drops below 5 ppm; usually 4-12 hours after a shock.
Around 30-50 standard pool shocks for a 30 m3 pool.
Yes, when fully pre-dissolved. Never broadcast dry granules onto a vinyl liner.
Only as a periodic CYA reset shock. Daily dosing in hot tubs should use SDIC, TCCA tablets or bromine.
Calcium hypochlorite (Ca(OCl)2) at >= 65% available chlorine.
Each calcium hypochlorite molecule releases one calcium ion alongside two chlorines.
Stabilised chlorine builds CYA. Calcium hypochlorite delivers chlorine without CYA, ideal for indoor pools and CYA-saturated water.
Granules added dry or pH out of band. Filter for 24 hours and dose clarifier.
Dose pH minus per the table to bring pH back to 7.4.
Clean filter overnight, vacuum dead algae, dose clarifier.
Calcium hypochlorite is unstabilised, alkaline and adds calcium. SDIC is stabilised, pH-neutral and adds CYA.
Both are unstabilised chlorine. Granules are easier to store and dose; liquid bleach is faster to dose but harder to handle.
Which shock treatment to reach for: weekly upkeep with non-chlorine shock, or recovery of neglected water with chlorine shock.
| What matters | Non-chlorine shock (MPS) | Chlorine shock (calcium hypochlorite) |
|---|---|---|
| Best for | Weekly upkeep after normal bathing | Recovering cloudy, green or neglected water |
| How it works | Oxidises bather waste so your sanitiser is freed up to disinfect | Raises free chlorine sharply to kill bacteria and algae outright |
| Effect on your sanitiser | Adds no chlorine; also reactivates spent bromide in bromine tubs | Adds a large chlorine dose on top of your routine level |
| Time before bathing | Short; retest and bathe once the water has circulated | Wait until free chlorine falls back below 5 ppm |
| How often | Weekly, and after heavy use or guests | Occasionally, when the water needs a reset |
| Typical cost per treatment | Low; a small regular dose | Low; a stronger dose used far less often |