pH plus - Sodium Carbonate

Raise hot tub or pool pH using pure sodium carbonate (soda ash). Lifts pH back above 7.2 without affecting calcium hardness, ideal after a chlorine shock or a heavy bather load.

• Raises pH by approximately 0.2 units per 16 g per 1000 L.
• Has minimal effect on total alkalinity at normal dosing.
• Stops eye stinging and metallic taste caused by acidic water.
• Protects heater elements, jet seals and pump O-rings from acid attack.
• Stabilises the sanitiser without overshooting into the scaling zone.

Sizes and prices

• 1kg: £6.52
• 2.5kg: £10.91
• 5kg: £18.23
• 10kg: £32.88
• 20kg: £62.16
• 25kg: £76.80

When you need it

• A fresh test strip reads below pH 7.2.
• Bathers report stinging eyes or a metallic taste.
• You have just shocked with a chlorine donor that depressed pH.
• Heater seals or jet faces show pitting or corrosion.
• Sanitiser is gassing off quickly even at low temperatures.

How to use

1. Test pH and total alkalinity using a fresh strip or liquid kit.
2. Calculate the dose; add no more than half in one go.
3. Switch the circulation pump on and remove any floating dispenser.
4. Pre-dissolve the dose in 5 L of warm tub water and stir until fully clear.
5. Pour the solution slowly around the surface of the tub.
6. Wait 30-60 minutes, retest, and only redose if pH is still below 7.2.

Dosing guide

Half-dose, retest, then top up. If pH is below 7.0 and TA is also low, dose Total Alkalinity Increaser first; the buffer will lift pH on its own.

• For 1,000 L, add 16 g to reach +0.2 pH.
• For 1,500 L, add 24 g to reach +0.2 pH.
• For 2,000 L, add 32 g to reach +0.2 pH.
• For 5,000 L, add 80 g to reach +0.2 pH.
• For 10,000 L, add 160 g to reach +0.2 pH.
• For 20,000 L, add 320 g to reach +0.2 pH.

How it works

Sodium carbonate (Na2CO3), commonly called soda ash. Supplied as a high-purity light powder with at least 99% active content.

Sodium carbonate dissolves to release carbonate ions, which combine with hydrogen ions in the water and raise pH. At normal dosing it adds very little long-term alkalinity because most of the carbonate vents as carbon dioxide once balance is restored.

Acidic water below pH 7.0 corrodes heater elements, dissolves metal seals and irritates skin and eyes. Holding pH 7.2-7.6 protects equipment, balances bather comfort, and keeps every gram of sanitiser working at its full kill rate.

Frequently asked questions

What is the ideal hot tub pH?

7.2-7.6 for chlorine and bromine systems. Below 7.0 corrodes equipment; above 7.8 scales surfaces.

Does pH plus raise alkalinity?

Only a little. Sodium carbonate adds about 4-6 ppm of TA per 0.2 pH lift.

How long until I can bathe?

Wait 60 minutes with the pump on, then retest. Once pH is in band you can bathe.

How long does a 1 kg pack last?

A 1500 L hot tub uses 24 g per dose, so 1 kg covers around 40 doses or 8-12 months of monthly maintenance.

Is it the same as washing soda?

Yes, food-grade sodium carbonate is chemically identical to washing soda. ClearSpa supplies a 99%+ pool-grade powder for fast, clean dissolving.

Will it work after a chlorine shock?

Yes. Chlorine shocks depress pH; pH plus is the standard fix once chlorine reads under 5 ppm.

Why does pH plus barely affect alkalinity?

Carbonate ions raise pH by absorbing protons but vent as CO2 once balance is restored, leaving little net alkalinity change.

Can I use it in a salt-water tub?

Yes. Salt chlorinators tend to push pH up, so you will use pH plus less often than tablet systems.

Does it raise total dissolved solids?

Only marginally. 100 g per 1000 L adds about 100 ppm TDS.

What if pH rises above 7.8?

Dose 16 g of pH minus per 1000 L to bring it back to 7.4; retest after 60 minutes.

Why is the water cloudy now?

Adding sodium carbonate neat or hitting pH above 7.8 can precipitate calcium. Filter for 24 hours and dose clarifier.

Why does the pH keep crashing back?

Low alkalinity lets pH drift. Dose Total Alkalinity Increaser to 80-100 ppm first.

pH plus vs total alkalinity increaser?

pH plus (sodium carbonate) raises pH with little TA gain. TA increaser (sodium bicarbonate) raises TA without much pH change.

pH plus vs borax?

Borax also raises pH but adds borate buffering. Sodium carbonate is the standard choice for routine UK hot tub care.