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How to raise your pool’s pH

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Low pH is corrosive: it eats heater cores and etches plaster. Which product you use depends on your alkalinity. If alkalinity is also low, soda ash fixes both. If alkalinity is fine, aeration raises pH for free without touching it.

Why low pH matters

The CDC notes that below pH 7.0 pool and hot tub pipes are more likely to corrode or break down, and it recommends keeping pH between 7.0 and 7.8. The MAHC Annex adds that low pH dissolves calcium carbonate from plaster and speeds metal corrosion.

Step by step

  1. Test pH and total alkalinity togetherThese two decide the fix. Alkalinity is the buffer holding pH steady, so a pool that keeps falling low almost always has low TA underneath.
  2. If alkalinity is also low, use soda ashSoda ash (sodium carbonate) raises pH strongly and alkalinity moderately, which is right when both are down. In 10,000 gallons at TA 80, raising pH from 7.2 to 7.5 takes about 14 oz of soda ash and lifts alkalinity about 10 ppm. Use the calculator for your numbers.
  3. If alkalinity is fine, just aerateAeration drives off dissolved carbon dioxide, which raises pH and leaves alkalinity alone; the MAHC Annex describes alkalinity as a source of rising pH for exactly this reason. Point returns upward, run a fountain or spa jets, or run a waterfall. It costs nothing but time.
  4. Pre-dissolve and add slowlyDissolve soda ash in a bucket of water and pour it around the pool with the pump running. Adding too much at once clouds the water and can leave a scale deposit.
  5. Re-test after the water has circulatedLet the pump turn the whole pool over, then re-test before adding more. Back-to-back doses based on early readings overshoot.

FAQ

Baking soda or soda ash to raise pH?

Soda ash (sodium carbonate) for pH. It moves pH a lot and alkalinity a little. Baking soda (sodium bicarbonate) is the opposite: it raises alkalinity with only a small pH nudge. Pick based on which reading is actually low.

Can I use borax to raise pH?

Yes. Borax raises pH with less effect on alkalinity than soda ash, which makes it useful when pH is low but TA is already at the top of range.

Why does my pool pH keep dropping?

Usually low alkalinity, so nothing buffers it. The MAHC Annex notes that with low alkalinity, acidic chlorine sources such as trichlor and dichlor can drop pH quickly. Fix alkalinity first and pH stops wandering.

Is low pH dangerous?

For the pool, yes. The CDC notes that below 7.0 pipes and equipment are more likely to corrode, and the MAHC Annex adds that low pH dissolves plaster. The CDC range to keep swimming water in is 7.0–7.8.

Sources

  1. CDC, Home Pool and Hot Tub Water Treatment and Testing (May 10, 2024). The 7.0–7.8 range and corrosion below 7.0
  2. CDC, Model Aquatic Health Code, 5th edition (2024), Code Language. Section 5.7.3.4.1: pH 7.0–7.8
  3. CDC, Model Aquatic Health Code, 5th edition (2024), Annex. Sections 5.7.3.4 (low pH and plaster), 5.7.4.4.1 (pH rise from carbon dioxide, acidic chlorine sources)

Related

Alkalinity calculatorHow to lower pool pHWater balance (LSI)

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