pH plus - Sodium Carbonate

Lift hot tub or pool pH with pure sodium carbonate, or soda ash. It nudges pH back over 7.2 without touching calcium hardness, which makes it the go-to after a chlorine shock or a busy session with lots of bathers.

• Raises pH by about 0.2 units for every 16 g added per 1000 L.
• Barely touches total alkalinity at normal doses.
• Stops the eye stinging and metallic taste that acidic water brings.
• Shields heater elements, jet seals and pump O-rings from acid attack.
• Steadies the sanitiser without tipping the water into the scaling zone.

Sizes and prices

Available in 1kg, 2.5kg, 5kg, 10kg, 20kg, 25kg.

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

How to use

1. Test pH and total alkalinity with a fresh strip or liquid kit.
2. Work out the dose and add no more than half of it in one go.
3. Switch the circulation pump on and lift out any floating dispenser.
4. Dissolve the dose in 5 L of warm tub water and stir until it is completely clear.
5. Pour the solution slowly around the surface of the tub.
6. Give it 30-60 minutes, retest, and only add more if pH is still under 7.2.

Frequently asked questions

What is the right hot tub pH?

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

Will pH plus raise alkalinity?

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

How long before I can get in?

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

How far does a 1 kg pack go?

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

Is it the same as washing soda?

Yes, food-grade sodium carbonate is chemically the same as washing soda. Zagosa Spa & Pool supplies a 99%+ pool-grade powder that dissolves fast and clean.

Can I use it after a chlorine shock?

Yes. Chlorine shocks knock pH down, and pH plus is the usual fix once chlorine reads under 5 ppm.

Why does pH plus barely change alkalinity?

Carbonate ions raise pH by soaking up protons, but they vent off as CO2 once balance returns, leaving little net alkalinity change.

Is it fine in a salt-water tub?

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

Does it raise total dissolved solids?

Only a little. 100 g per 1000 L adds roughly 100 ppm TDS.

What if pH goes over 7.8?

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

Why is the water cloudy now?

Adding sodium carbonate neat, or overshooting pH above 7.8, can precipitate calcium. Filter for 24 hours and add a clarifier.

Why does pH keep crashing back down?

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

pH plus or total alkalinity increaser?

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

pH plus versus borax?

Borax also lifts pH but brings borate buffering with it. Sodium carbonate is the standard pick for everyday UK hot tub care.