Calcium Hardness Increaser - Calcium Chloride Flakes

Raise calcium hardness in hot tubs and pools fast with food-grade calcium chloride flakes. Soft water below 150 ppm causes corrosion and foaming. Restore the 150-250 ppm safe band in one dose.

• Increases total calcium hardness by approximately 10 ppm per 9 g per 1000 L.
• Protects acrylic shells, jet bearings and heater elements from soft-water corrosion.
• Stops persistent foaming caused by water that is too soft.
• Stabilises pH and prevents wild swings during heating cycles.
• Dissolves quickly in warm water with no cloudy residue when added correctly.

Sizes and prices

• 1kg: £10.79
• 2.5kg: £15.10
• 5kg: £22.29
• 10kg: £36.67
• 20kg: £65.42
• 25kg: £79.80

When you need it

• A test strip reads below 150 ppm calcium hardness.
• Water has been refilled from a soft-water source or a domestic softener.
• Foam keeps returning even after dosing antifoam.
• Acrylic shell, jets or pillows feel etched, dull or chalky.
• Heater is short-cycling or showing premature element failure.

How to use

1. Test current calcium hardness, total alkalinity and pH with a fresh strip or liquid kit.
2. Switch the circulation pump on and remove the floating dispenser.
3. Pre-dissolve the required dose in a clean bucket of warm tub water (about 5 L) and stir.
4. Pour the dissolved solution slowly across the surface of the tub with the pump running.
5. Run circulation for at least 4 hours before bathing or retesting.
6. Retest after 4 hours and only redose if hardness is still below 150 ppm.

Dosing guide

Doses below assume a starting hardness within 0-150 ppm. Always pre-dissolve, run the pump for 4 hours, then retest before redosing.

• For 1,000 L (small spa), add 9 g to reach +10 ppm.
• For 1,500 L (typical hot tub), add 27 g to reach +20 ppm.
• For 2,000 L (large hot tub), add 54 g to reach +30 ppm.
• For 5,000 L (small swim spa), add 225 g to reach +50 ppm.
• For 10,000 L (small pool), add 450 g to reach +50 ppm.
• For 20,000 L (mid-size pool), add 1,800 g to reach +100 ppm.

How it works

Pharmaceutical-grade calcium chloride dihydrate (CaCl2.2H2O) supplied as fast-dissolving white flakes. The flake form has a higher surface area than pellets and dissolves cleanly without leaving a chalky residue.

When CaCl2 dissolves it dissociates into one calcium and two chloride ions. The calcium contributes directly to the calcium-hardness reading and to the Langelier Saturation Index. Raising the Ca level pushes water away from the aggressive (low-hardness) side of the LSI scale and back into balance.

Soft water is chemically aggressive: it dissolves calcium out of plaster, etches acrylic shells, attacks heater elements and produces stubborn foam. Holding 150-250 ppm calcium hardness extends equipment life, reduces antifoam use and stabilises pH between water changes.

Frequently asked questions

What is the ideal calcium hardness for a hot tub?

Hold calcium hardness between 150 ppm and 250 ppm for hot tubs and 200-400 ppm for swimming pools.

How much does 9 g raise calcium hardness?

Approximately 10 ppm in 1000 L of water at room temperature.

Is calcium chloride safe for acrylic spas?

Yes, when pre-dissolved in a bucket and added with the pump running. Never broadcast dry flakes onto an acrylic shell.

How long does a 1 kg tub last?

A 1500 L hot tub typically uses 25-50 g per top-up, so 1 kg covers 20-40 doses or roughly a year of normal use.

Will it work in a salt-water pool?

Yes, calcium chloride is fully compatible with salt chlorination systems and does not interfere with the cell.

Do I need to shock the tub afterwards?

No, calcium chloride is a balancer not a sanitiser. Sanitiser levels are unaffected.

Why are flakes better than pellets?

Flakes have a larger surface area, so they dissolve faster and leave less chance of pooling on the shell.

Does it raise total dissolved solids (TDS)?

Yes. Each 100 ppm of added hardness raises TDS by roughly 280 ppm. Refresh part of the water if TDS exceeds 1500 ppm.

How does calcium hardness link to LSI?

Calcium is one of the four LSI inputs alongside pH, alkalinity and temperature. Raising Ca hardness moves water away from the corrosive end of the index.

Why is my water cloudy after dosing?

Either the flakes were added neat, or pH was already above 7.8. Run circulation for 24 hours and add a clarifier; lower pH if needed.

Can I use it to fix scale?

No. Scale is the opposite problem; use Water Scale Inhibitor and lower pH to dissolve existing scale.

Why is foaming worse after dosing?

Foam unrelated to softness can be caused by lotions, detergents or low-quality antifoam; clean the filter and add an antifoam designed for hot tubs.

Calcium chloride vs calcium hypochlorite?

Calcium chloride only raises hardness; calcium hypochlorite is a strong sanitiser that also raises pH and chlorine. They are not interchangeable.

Calcium chloride flakes vs prills?

Both contain the same active ingredient. Flakes dissolve faster, prills are denser and easier to scoop. ClearSpa supplies flakes for fastest dissolution in heated water.