How to Raise pH in a Pool Without Wrecking Your Alkalinity
Almost every page on this question says to add soda ash or baking soda, as though the two were alternatives. They are not, and choosing the wrong one is the single most common reason somebody spends a week chasing a pH reading that will not stay put.
Test alkalinity before you touch the pH
Total alkalinity is the buffer that holds pH in place. Correct pH while alkalinity is too low and the reading drifts back within days, which is what makes this feel like an unfixable problem rather than a two-hour job.
So the order is: read alkalinity first, fix it if it is low, then read pH again. It will often have moved on its own.
The two chemicals do different jobs
| Chemical | What it actually moves | Reach for it when |
|---|---|---|
| Soda ash (sodium carbonate) | pH, strongly. Alkalinity, slightly | Alkalinity is fine and pH alone is low |
| Baking soda (sodium bicarbonate) | Alkalinity, strongly. pH, slightly | Alkalinity is low, whatever pH says |
| Aeration (no chemical) | pH up, alkalinity unchanged | pH is low, alkalinity is already correct |
That third row is the one worth knowing about. Pointing a return jet upward, or running a spa jet or fountain, drives carbon dioxide out of the water and raises pH without adding anything at all. It is slow, and it costs nothing.
What to add, and how much
Our pool chemical calculator uses these rates, which are the ones the doses below come from:
- Soda ash: about 6 oz raises pH by roughly 0.1 in 10,000 gallons, when alkalinity is near neutral.
- Baking soda: about 1.5 lbs raises total alkalinity by 10 ppm in 10,000 gallons.
For a 20,000 gallon pool reading pH 7.0, moving to 7.5 is five steps of 0.1, so about 60 oz of soda ash, a little under 4 lbs. The same pool needing alkalinity lifted from 60 ppm to 90 ppm takes about 9 lbs of baking soda.
Both of those depend entirely on knowing your actual volume. An estimate that is 20 percent out makes every dose you ever add 20 percent out with it, so if you have never measured, the pool volume calculator is the place to start.
Add no more than half a dose at a time. Broadcast it slowly over the deep end with the pump running, give it half an hour to circulate, then retest. Chasing the number with a second full dose before the first has mixed is how a low pH becomes a high one.
What you are aiming for
The CDC recommends a pH of 7.0 to 7.8 for pools and hot tubs, and testing chlorine and pH at least twice a day, more when a lot of people are swimming. Our calculator defaults to 7.5 as a target because it sits comfortably inside that range with room on both sides for the ordinary daily drift.
There is a real reason to care beyond comfort. As pH climbs, chlorine loses its ability to kill germs, and the CDC singles out readings above 8.0 as the point where that becomes a problem. Low pH has its own costs: it is corrosive to metal fittings, heater cores and plaster, and it stings eyes.
When it will not hold
If pH keeps falling back after a correct dose, stop dosing pH and look at these instead.
- Alkalinity below about 80 ppm. The buffer is not there. This is the common answer.
- Heavy rain. Rainwater is acidic and a big storm can move a pool several tenths on its own.
- A salt cell or an acid feeder doing its job on a schedule rather than in response to a reading.
- Fresh plaster. A new or resurfaced pool leaches for months and its chemistry is not representative of how it will behave later.
Fix the cause and the pH stops being a weekly chore. Chase the reading without fixing it, and you will be back here next Saturday.
If your alkalinity turns out to be the problem in the other direction, the companion to this page is pool chemistry in the right order, which covers what to correct first when more than one number is wrong.
Frequently asked questions
How long after adding soda ash can I swim?
Once it has fully circulated and the water is clear, usually about an hour with the pump running. Soda ash raises pH rather than sanitizer level, so the wait is about dissolution and cloudiness rather than about chlorine. Retest before you get in, and if the water is still hazy, give the filter more time.
Why does my pH keep dropping back down?
Low total alkalinity is the usual cause. Alkalinity is the buffer that holds pH steady, and below roughly 80 ppm the pH swings on almost nothing: rain, a heavy swim day, an acid dose. Raise alkalinity with baking soda first, then correct pH, and the reading tends to stay where you put it.
Can I use baking soda to raise pH?
It does raise pH slightly, but it moves alkalinity far more, so using it to chase a pH reading usually ends with alkalinity too high and a pH that is still not where you wanted it. If your alkalinity is already in range, soda ash is the tool for the job.
Is aeration really enough to raise pH?
Sometimes, and it is free. Running a fountain, a spa jet or a return pointed upward drives carbon dioxide out of the water, which raises pH without adding anything. It is slow and it will not fix a pool that is genuinely far off, but it is the right first move when pH is low and alkalinity is already where you want it.