How to raise pH in a hot tub

Quick answer

Add soda ash (sodium carbonate, sold as pH increaser) sized to your water volume, with the pump running, in small steps. Wait, then retest. Aim for pH 7.2 to 7.8. If your total alkalinity is also low, use baking soda (sodium bicarbonate) instead, which raises alkalinity and brings pH up with it.

Size my dose

Low pH is less common than high pH, but harder on your tub: below about 7.2 the water turns corrosive, stings eyes and skin, and eats at metal heater elements and seals. It is worth fixing promptly.

Soda ash or baking soda?

The choice depends on your alkalinity reading. Soda ash raises pH strongly with only a small effect on alkalinity, so use it when pH is low but alkalinity is fine. Baking soda raises alkalinity and pulls pH up gently with it, so use it when both are low. The dosing calculator sizes the alkalinity raise with baking soda; for a pure pH lift, a spa pH increaser is soda ash.

Step by step

Test pH and total alkalinity.
If alkalinity is also low, size a baking soda dose first; it often brings pH into range on its own.
If pH is still low with alkalinity in range, add soda ash in small steps with the pump running.
Circulate, wait, and retest. Soda ash is strong, so go slowly to avoid overshooting high.

Add in small steps with the pump running, wait, then retest before adding more. Never mix chemicals together, and always follow your product label, which wins over any calculator.

What to use

For a pure pH lift, a soda ash pH increaser. If alkalinity is also low, a sodium bicarbonate alkalinity increaser does both jobs.

Get spa ph increaser (soda ash) Get spa alkalinity increaser

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Common questions

I added soda ash and the water went cloudy. Why?

A large soda ash dose can briefly cloud water and can spike pH high enough to cloud it with scale. Add in small steps with the pump running, and the cloudiness usually clears as it circulates. If it lingers, see the cloudy water guide.

Can I just use baking soda for everything?

Baking soda is great when alkalinity is low, but it barely moves pH once alkalinity is already in range. To raise pH without pushing alkalinity too high, soda ash is the right tool.

How low is too low to soak?

Below about 7.0 the water is acidic enough to irritate skin and eyes and to corrode metal. Raise it before a long soak, and check that low pH is not a sign your alkalinity has crashed.