Pool Calcium Hypochlorite Granules - Unstabilised Shock Sanitiser

Unstabilised calcium hypochlorite granules at 65% available chlorine. The fastest hard-hitting pool chlorine for shocks, indoor pools and over-stabilised water where SDIC has stopped working.

• Adds 1 ppm of free chlorine per 15 g per m³.
• No cyanuric acid, ideal for indoor pools and pools with high CYA.
• Hits algae, biofilms and chloramines fast at shock concentrations.
• Dissolves in 1-2 minutes when pre-dissolved correctly.
• Raises pH and adds calcium hardness as a side effect.

Sizes and prices

• 5kg: £42.00
• 10kg: £83.75
• 25kg: £209.00

When you need it

• You need a fast shock to clear algae or chloramines.
• Cyanuric acid is over 80 ppm and chlorine is locked up.
• You run an indoor pool where stabiliser is unwelcome.
• Calcium hardness is below 150 ppm and needs raising anyway.
• Liquid chlorine is impractical to handle or store.

How to use

1. Test pH, alkalinity, free chlorine and CYA before dosing.
2. Brush the pool, lower water to circulation only and switch off automatic dosers.
3. Pre-dissolve the dose in a 10 L bucket of pool water and let any sediment settle.
4. Pour the clear solution slowly across the deep end with the pump on.
5. Discard sediment in a separate diluted bucket; never tip back into the pool.
6. Test free chlorine after 4 hours; do not bathe until below 5 ppm.

Dosing guide

Cal-hypo raises pH approximately 0.2 per 1 ppm shock. After dosing, retest pH and dose pH Minus to bring back into 7.2-7.6 band. Calcium hardness will also rise; monitor monthly.

• For 20 m³, add 300 g to reach Raise 1 ppm chlorine.
• For 40 m³, add 600 g to reach Raise 1 ppm chlorine.
• For 20 m³, add 1.5 kg to reach Standard shock to 5 ppm.
• For 40 m³, add 6 kg to reach Algae shock to 10 ppm.
• For 60 m³, add 18 kg to reach Black-spot algae shock to 20 ppm.

How it works

Calcium hypochlorite granules at 65% available chlorine. Unstabilised, no cyanuric acid; releases chlorine and calcium together on contact with water.

Cal-hypo dissolves to give hypochlorous acid (HOCl), the active oxidiser, plus calcium ions and a strong rise in pH. Without stabiliser, all chlorine is bioavailable straight away, which is why it is so effective for shocks.

When cyanuric acid is too high or you need to break a chloramine ceiling, only an unstabilised oxidiser will work. Cal-hypo is the standard tool for that job and the fastest sanitiser in any pool plant room.

Frequently asked questions

How much for a shock?

75 g per m³ for a standard 5 ppm shock; 150 g per m³ for a 10 ppm algae shock.

Do I have to pre-dissolve?

Yes. Always pre-dissolve in a 10 L bucket of pool water; broadcasting cal-hypo dry can bleach vinyl and stain plaster.

How long until I can swim?

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

Why no cyanuric acid?

Indoor pools and high-CYA pools need bioavailable chlorine. Cal-hypo gives 100% active chlorine with no stabiliser added.

How long does a 5 kg pack last?

Around 8-10 standard shocks for a 40 m³ pool, longer if used only as an emergency oxidiser.

Can I use it in vinyl pools?

Yes, provided you pre-dissolve and pour the clear solution; never tip undissolved sediment in.

What is the active ingredient?

Calcium hypochlorite at 65% available chlorine, unstabilised.

How does it raise pH?

Hypochlorite ion combines with water to give hydroxide; cal-hypo dissolves alkaline at around pH 11.

Why is it incompatible with TCCA?

Cal-hypo is alkaline and oxidising; TCCA is acidic and chlorinated. Mixed dry they can ignite.

Cloudy after shock?

pH likely spiked; drop with pH Minus and run filtration 12 hours.

Calcium too high?

Switch to SDIC for routine; partial drain if above 400 ppm.

Cal-hypo vs SDIC?

Cal-hypo is unstabilised and faster but pH-raising; SDIC is stabilised, pH-neutral and gentler. Use cal-hypo for shocks, SDIC for routine.

Cal-hypo vs liquid chlorine?

Cal-hypo is storable for months and easy to ship; liquid chlorine decays in storage but is cheaper per active ppm. Choose cal-hypo for low usage, liquid for daily plant rooms.