Spa Calcium Hypochlorite Granules

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.

• Adds 1 ppm of free chlorine per 1.5 g per 1000 L.
• Burns through algae blooms and high combined chlorine.
• Adds calcium hardness (~7 ppm per 5 g per 1000 L).
• Free of cyanuric acid; ideal for indoor pools.
• Suitable for periodic super-chlorination of spas with high CYA.

Sizes and prices

• 1kg: £13.25
• 2.5kg: £23.85
• 5kg: £41.52
• 10kg: £76.86
• 20kg: £147.53
• 25kg: £182.87

When you need it

• An algae bloom has appeared in a pool.
• Combined chlorine is above 1 ppm and MPS has not cleared it.
• Cyanuric acid is over 50 ppm and chlorine is no longer effective.
• The pool or indoor spa needs a fast chlorine kick.
• You have just opened the pool for the season.

How to use

1. Test free chlorine, pH, alkalinity and CYA.
2. Confirm pH is 7.2-7.6 before shocking.
3. Pre-dissolve the dose in 10 L of warm water (use a clean plastic bucket).
4. Switch the pump to circulation and pour solution slowly across the surface.
5. Run circulation for at least 4 hours; do not bathe.
6. Wait until free chlorine drops below 5 ppm before bathing.

Dosing guide

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.

• For 1,000 L, add 1.5 g to reach +1 ppm.
• For 1,500 L, add 11 g to reach +5 ppm shock.
• For 10,000 L (pool), add 75 g to reach +5 ppm shock.
• For 20,000 L (pool), add 150 g to reach +5 ppm shock.
• For 50,000 L (large pool), add 750 g to reach +10 ppm super.

How it works

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.

Frequently asked questions

How much to add for a 5 ppm shock?

Approximately 7.5 g per 1000 L of water, pre-dissolved in 10 L of warm water before adding.

Does it raise pH?

Yes. Each 1 ppm of chlorine added with calcium hypochlorite lifts pH by about 0.05 units.

How long until I can bathe?

Wait until free chlorine drops below 5 ppm; usually 4-12 hours after a shock.

How long does a 5 kg pack last?

Around 30-50 standard pool shocks for a 30 m3 pool.

Is it safe for vinyl liners?

Yes, when fully pre-dissolved. Never broadcast dry granules onto a vinyl liner.

Can I use it in a hot tub?

Only as a periodic CYA reset shock. Daily dosing in hot tubs should use SDIC, TCCA tablets or bromine.

What is the active ingredient?

Calcium hypochlorite (Ca(OCl)2) at >= 65% available chlorine.

Why does it raise calcium?

Each calcium hypochlorite molecule releases one calcium ion alongside two chlorines.

Why use unstabilised chlorine?

Stabilised chlorine builds CYA. Calcium hypochlorite delivers chlorine without CYA, ideal for indoor pools and CYA-saturated water.

Cloudy water after shock?

Granules added dry or pH out of band. Filter for 24 hours and dose clarifier.

pH spike after shock?

Dose pH minus per the table to bring pH back to 7.4.

Algae returning?

Clean filter overnight, vacuum dead algae, dose clarifier.

Calcium hypo vs SDIC?

Calcium hypochlorite is unstabilised, alkaline and adds calcium. SDIC is stabilised, pH-neutral and adds CYA.

Calcium hypo vs liquid bleach?

Both are unstabilised chlorine. Granules are easier to store and dose; liquid bleach is faster to dose but harder to handle.