Test-strip pads showing color tones held above glowing teal water

How to raise pH in a hot tub

The quick version

To raise pH in a hot tub, 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

pH too high instead? How to lower pH in a hot tub → · Alkalinity low as well? How to raise alkalinity →

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.

The steps

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.

Go in small steps with the water moving, pause, retest, then decide on more. Never mix one chemical with another; the label on the container beats any guide, including this one.

The right product

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

Where these numbers come from

Every dose on this page is computed from the standard published rates in these references, and the build re-checks each constant against them before the site ships (how the checking works).

Taylor Technologies dosage tables · the standard pool and spa water-chemistry dosage reference the dosing constants are calibrated against
PoolMath (Trouble Free Pool) · the public pool and spa dosing calculator the constants are cross-checked with
Pool & Hot Tub Alliance (PHTA) · the industry association whose balanced-water guidance sets the target ranges

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.