Why Your Hot Tub pH Won't Hold (and How to Fix It)

Quick answerpH that keeps sagging means your water has no buffer: total alkalinity is too low. Raise TA to 80–120 ppm with alkalinity increaser (baking soda works — it's the same compound), and pH will stop crashing. Chasing pH with pH-up while TA is low is a treadmill.

The buffer problem

Total alkalinity absorbs acid hits — from sanitizer (dichlor and bromine tablets are acidic), rain, and bather load. With TA under ~80 ppm, there's nothing to absorb them, so every soak knocks pH down and every pH-up dose evaporates in a day or two. Symptoms of chronically low pH: eye and skin sting, itchy feeling, corrosion on metal fittings, and sanitizer that vanishes fast.

Fix the buffer, then the pH

Test TA. If it's under 80 ppm, this is your answer.
Add alkalinity increaser (sodium bicarbonate) with jets on. Roughly 1 tbsp per 100 gallons raises TA ~10 ppm; follow your label. Plain Arm & Hammer baking soda is chemically identical and cheaper.
Wait an hour, retest, repeat to reach 80–120 ppm.
Recheck pH. It usually rises with TA; if it's still under 7.2, a small dose of pH increaser finishes the job.
Retest in 2–3 days. If TA holds, pH will hold.

If TA is fine but pH still drops

Look at your sanitizer. Dichlor granules and bromine tablets are both acidic — heavy use pulls pH down continuously. That's normal; the fix is keeping TA in range so the pull is slow, and accepting a small pH-up dose every week or two. Also check for a heavily used ozonator or frequent MPS shocking, both mildly acidifying.

What you'll need

Alkalinity increaserRestores the buffer so pH stops crashing.
pH increaser (soda ash)For the final nudge once TA is in range.
Test strips (7-way)TA is the reading that matters here — test it every time.

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Common questions

What causes hot tub pH to keep dropping?

Low total alkalinity. TA under 80 ppm means the water has no buffer, so acidic sanitizers and bather load drag pH down after every correction.

Can I use baking soda to raise alkalinity in a hot tub?

Yes. Alkalinity increaser is sodium bicarbonate — the same compound as baking soda. Dose roughly 1 tablespoon per 100 gallons for a ~10 ppm increase, and retest.

Is low pH bad for my hot tub?

Yes — acidic water corrodes heater elements, pump seals, and metal trim, and it stings eyes and skin. Chronic low pH is one of the most expensive chemistry problems to ignore.

Want exact doses for your tub's volume and sanitizer system? Use the free Spa Assistant — test, enter your readings, get a dosing plan.