Pool Calcium Hardness Increaser

Calcium chloride flake hardness increaser for swimming pools. Lifts calcium hardness 10 ppm per 9 g per m³ to stop soft-water corrosion of plaster, grout and metal heater elements.

• Raises calcium hardness approximately 10 ppm per 9 g per m³.
• Stops soft-water etching of plaster and grout.
• Stabilises pH and stops sudden swings.
• Cuts foaming on heavily aerated pools.
• Protects bare-metal heater elements from leaching.

Sizes and prices

• 5kg: £26.00
• 10kg: £46.75
• 25kg: £109.00

When you need it

• Calcium hardness reads below 150 ppm.
• Plaster surface looks chalky or grout is washing out.
• Persistent foaming on jets and waterfalls.
• Newly filled pool with soft mains water.
• Heater warranty requires hardness 200-400 ppm.

How to use

1. Test calcium hardness, pH and TA from a fresh sample.
2. Calculate dose: 9 g per m³ raises hardness by approximately 10 ppm.
3. Pre-dissolve in a 10 L bucket of warm pool water (water gets warm; this is normal).
4. Pour solution slowly across the deep end with circulation on.
5. Run filtration 6 hours.
6. Retest calcium and pH; expect a small pH lift.

Dosing guide

Doses are starting points; always retest 4-6 hours after dosing. Calcium chloride lifts pH slightly; recheck pH before correcting.

• For 20 m³, add 180 g to reach Lift calcium 10 ppm.
• For 40 m³, add 360 g to reach Lift calcium 10 ppm.
• For 60 m³, add 540 g to reach Lift calcium 10 ppm.
• For 40 m³, add 1.8 kg to reach Lift calcium 50 ppm.
• For 100 m³, add 900 g to reach Lift calcium 10 ppm.

How it works

Calcium chloride (CaCl2) at 77-80% purity, supplied as fast-dissolving food-grade flakes.

Calcium chloride dissolves exothermically to release calcium and chloride ions. The calcium binds carbonate to stabilise scale balance; the chloride is inert and adds no chlorine.

Soft water (under 150 ppm calcium) is aggressive: it strips calcium from plaster, grout, tile mortar and metal heaters to satisfy its own chemistry. Hard water (over 400 ppm) deposits calcium scale. The 200-300 ppm sweet spot keeps surfaces stable.

Frequently asked questions

How much do I dose?

9 g per m³ lifts calcium 10 ppm. For a 40 m³ pool that is 360 g per 10 ppm.

Will it cloud my water?

Briefly. Pre-dissolve and run filtration 12 hours; cloud clears.

What range should I aim for?

200-300 ppm for plaster pools; 150-250 ppm for vinyl liner pools.

Pack sizes?

5 kg, 10 kg and 25 kg sacks of food-grade flakes.

How often do I need to dose?

Once per swim season for most pools, more often if you backwash heavily or top up from soft mains.

Is it food grade?

Yes, the same calcium chloride used in cheese-making and pickling; 77-80% purity.

What is the active ingredient?

Calcium chloride dihydrate at 77-80% purity.

Why exothermic?

Dissolving calcium chloride releases heat; pre-dissolve in 5-10 L of pool water for safety.

Will it add chlorine?

No. Calcium chloride contains chloride ion, not chlorine. No sanitiser effect.

Cloudy after dose?

Pre-dissolve next time; calcium precipitates briefly under high pH.

Calcium too high now?

Partial drain 25-30%; refill with mains water and retest.

Calcium chloride vs calcium carbonate?

Chloride dissolves fast and lifts hardness directly; carbonate is the scale form, not used as a dosing chemical.

Hardness increaser vs scale inhibitor?

Increaser lifts low hardness; inhibitor stops high hardness depositing as scale. Different problems, different chemicals.