How much muriatic acid to lower pool pH?
It depends on more than your pH reading — the same 7.8 takes nearly twice as much acid at TA 120 as at TA 60, because alkalinity is the water's resistance to pH change. That's why one-size answers ("add a cup") routinely overshoot or undershoot. Typical doses of 31.45% muriatic acid per 10,000 gallons, aiming for pH 7.5:
| Starting pH | TA 80 | TA 100 | TA 120 |
|---|---|---|---|
| 7.8 | 7 fl oz | 9 fl oz | 11 fl oz |
| 8.0 | 10 fl oz | 12 fl oz | 15 fl oz |
Unstabilized water. CYA and borates buffer too — a stabilized pool needs roughly 10–30% more, which the calculator above accounts for exactly. These chart values are verified against the calculator in our test suite.
pH measures the water's acidity, alkalinity measures its buffering — how much acid it can absorb before the pH actually moves. Every acid dose gets partly spent neutralizing bicarbonate before it shifts pH, which is also why every acid dose lowers your TA a little. The calculator reports that TA drop with each result.
How to lower pH in a pool
Muriatic acid is the standard tool: cheap, fast, and it leaves nothing behind. Dilute the measured dose in a bucket of pool water (acid into water, always), pour it slowly in front of a return jet with the pump running, and retest after 30–60 minutes of circulation. If your reading started at 8.0 or above, take it down in two doses — test kits read poorly at the top of the scale, so the first dose is aiming from a blurry starting point.
Dry acid (sodium bisulfate) works and is easier to handle, but every dose adds sulfates, which accumulate exactly like CYA does — and high sulfate levels attack plaster and salt-cell coatings. Fine for occasional use or spas; a poor daily driver, and worth avoiding altogether on SWG pools.
How to raise pH in a pool
Two tools, depending on your TA. If TA is low too, soda ash fixes both at once — the calculator above doses it and shows the TA rise. If TA is already where you want it, don't dose at all: aeration raises pH without touching TA. Point returns at the surface, run a fountain or waterfall, let a robot churn — off-gassing CO₂ is the only free chemical adjustment in pool care, it just takes a day or two.
And the perennial mix-up: baking soda barely moves pH. It's the alkalinity tool. If a guide tells you to raise pH with baking soda, you'll end up with sky-high TA and the same pH problem next week. Soda ash (sodium carbonate) and baking soda (sodium bicarbonate) are different chemicals with different jobs.
If you're dosing acid every few days, something is pushing back: high TA (drifts pH up constantly — fix the TA and the pH calms down), new plaster (curing raises pH for its entire first year), an SWG (the cell aerates the water), or any waterfall, spillover or fountain. Chasing pH without fixing the pusher is a subscription to muriatic acid.
What's the right pH target?
7.4–7.8 is the comfortable band; 7.5 is the default target this calculator aims for. Within that band, let your water-balance number (CSI) pick your spot: scaling-prone water runs better at 7.4–7.5, aggressive water at 7.6–7.8. Below 7.2 water stings eyes and corrodes; above 7.8 chlorine slows down and calcium starts looking for somewhere to precipitate. If your pH sits in band, leave it alone — a stable 7.7 beats a yo-yo between 7.4 and 7.8.