Your test kit just turned bright red and you have no idea if that means the water is too acidic or too basic, or what to pour in first. pH is the one chemistry number that affects everything else in the pool, and it moves fast.
What pH actually controls in your pool
pH is a measure of how acidic or basic your water is, on a scale of 0 to 14. Pool water should sit between 7.4 and 7.6, slightly alkaline, close to the pH of human tears, which is why that range feels comfortable on your eyes.
Here’s the part that surprises most pool owners: pH doesn’t just affect comfort. It controls how effective your chlorine is.
At pH 7.5, roughly 50% of your free chlorine exists as hypochlorous acid, the form that actually kills bacteria and algae. Raise that pH to 8.0 and the active fraction drops to about 21%. Your chlorine test might read a healthy 3 ppm, but almost 80% of it is sitting there doing nothing. You’d need to nearly double your chlorine dose just to maintain the same sanitation at pH 8.0 as you get at 7.5.
Low pH causes different damage. Below 7.2, water becomes corrosive. It eats at plaster, grout, and metal fittings. Swimmers complain of stinging eyes and dry skin. Rubber seals on pumps and heaters soften and fail early.
The target: 7.4 to 7.6, tested at least twice a week in summer. Everything else, chlorine, alkalinity, cyanuric acid, works better when pH is in that window.
Why San Diego pools drift high (and a few drift low)
Most San Diego pools run high, not low. A few reasons explain it.
San Diego tap water starts alkaline. The San Diego County Water Authority blends Colorado River water and State Project Water, both of which carry high mineral content and land around pH 7.8 to 8.2 coming out of the tap. You’re often fighting a drift toward high pH from the moment you fill.
Aeration pushes pH up. Waterfalls, spillways, spa jets, and even a good pump-and-filter cycle all off-gas carbon dioxide. When CO2 leaves the water, pH rises. A pool with a sheer-descent waterfall running eight hours a day will drift high faster than a still pool.
High total alkalinity buffers pH upward. Alkalinity is the pool’s pH buffer. When it’s above 120 ppm, common in San Diego fill water, it resists any acid you add and slowly pushes pH back toward its natural resting point: high. If you’re constantly adding acid but pH keeps creeping back up within two or three days, elevated alkalinity is usually the reason.
A smaller number of pools drift low. This typically happens after a heavy rain event that dumps freshwater into the pool, or when a pool owner over-adds acid and overshoots. Pools with a lot of bather load can also see pH drop as sweat and body oils consume alkalinity.
How to raise pH safely without spiking alkalinity
The right product to raise pH is sodium carbonate, also sold as soda ash or pH Up. Don’t confuse it with sodium bicarbonate (baking soda), which raises alkalinity more than pH.
Calculating your dose
A rough rule: 6 oz of soda ash raises pH by about 0.2 in a 10,000-gallon pool. Most San Diego backyard pools are 15,000 to 20,000 gallons.
Example: Your pool holds 18,000 gallons. pH is at 7.1 and you want to reach 7.5, a jump of 0.4. That means two 0.2-point doses.
- 6 oz per 10,000 gallons × 1.8 (for 18,000 gallons) = about 11 oz per dose
- Two doses needed = roughly 22 oz total, added in two separate rounds four hours apart
How to add it safely
- Test pH and total alkalinity before touching anything.
- Pre-dissolve the soda ash in a bucket of pool water. Pouring dry powder directly can leave white cloudy spots on plaster.
- Pour slowly near a return jet with the pump running.
- Wait four hours, then retest before adding a second dose.
The reason to split doses: soda ash also nudges alkalinity upward, and it’s easier to add more than to undo an overshoot. If your alkalinity is already high, say, above 100 ppm, consider aeration first. Running your pump, turning on water features, and leaving the pool uncovered overnight will naturally off-gas CO2 and push pH up without touching alkalinity.
How to lower pH without overshooting
The standard product for lowering pool pH is muriatic acid (hydrochloric acid), sold in pool supply stores at 31.45% concentration. Dry acid (sodium bisulfate) works too and is safer to handle, but costs more and you need about 1.6 times the dose for the same effect.
Calculating your dose
A general baseline: 10 oz of 31.45% muriatic acid lowers pH by about 0.2 in a 15,000-gallon pool. Your pool chemistry and alkalinity level will shift this slightly, so treat these numbers as a starting point.
Example: 15,000-gallon pool, pH at 7.9, target 7.4, a drop of 0.5. That’s roughly two and a half 0.2-point corrections.
- 10 oz × 2.5 = about 25 oz of muriatic acid, split across two additions
Never add more than 16 oz at once to a 15,000-gallon pool. Big single dumps create a low-pH dead zone near the entry point that can etch plaster.
How to add it safely
- Put on chemical-resistant gloves and eye protection. Muriatic acid fumes are harsh and it will burn skin on contact.
- With the pump running, pour slowly along the edge of the deep end, walking as you go. Don’t dump it all in one spot.
- Keep people and pets out of the pool for at least four hours.
- Retest before adding a second dose.
If your total alkalinity is above 100 ppm, lowering it first will make pH easier to control long-term. To lower alkalinity, add your muriatic acid in a single spot with the pump off, let it sit for an hour, then brush the area and turn the pump on. This targeted method preferentially drops alkalinity before pH. It takes a few rounds, but it’s how you break the cycle of constant acid additions.
If you’re dealing with high cyanuric acid alongside your pH issues, read our post on cyanuric acid levels in pools, the two problems often travel together in San Diego.
When to stop chasing it and call us
Some pH problems are a five-minute fix. Others are a symptom of something bigger.
Call a professional when:
- pH won’t hold for more than two or three days despite correct additions. This usually means alkalinity or cyanuric acid is out of range, or there’s a fill-water issue worth diagnosing properly.
- You’ve added acid multiple times and pH is still above 8.0. At that point, your chlorine isn’t sanitizing and you’re at real risk of an algae or bacteria problem.
- You’re seeing scale on tile or equipment. High pH combined with high calcium hardness deposits calcium carbonate on surfaces. That scale is expensive to remove, our pool tile and calcium cleaning service can handle what’s already there, but stopping the chemistry problem first prevents it from coming back.
- You’ve just opened the pool for the season and the water is cloudy. pH imbalance after a winter idle often shows up as cloudiness first, and there’s usually more than one number out of range.
The most reliable way to prevent all of this is consistent, weekly testing and adjustment. Our weekly pool cleaning and maintenance service includes chemistry checks and chemical balancing at every visit, so pH drifts get caught before they become a repair bill.
When to call us
pH problems that repeat week after week aren’t a chemical problem, they’re a water balance problem that needs a trained eye. If you’re spending more time testing and dosing than you are swimming, that’s a sign something upstream is off.
Call us at (760) 642-1256 for a same-day estimate.
Frequently asked questions
What is the ideal pH range for a pool?
The ideal range is 7.4 to 7.6. Anything below 7.2 is acidic enough to irritate eyes and corrode equipment. Anything above 7.8 sharply reduces chlorine effectiveness.
How much muriatic acid do I need to lower pH in a 15,000-gallon pool?
To drop pH from 7.8 to 7.5 in a 15,000-gallon pool, you typically need about 10 to 12 oz of 31.45% muriatic acid. Always test again after 4 hours before adding more.
Why does my pool pH keep going up even after I add acid?
High total alkalinity is the most common reason. When alkalinity is above 120 ppm, it acts as a buffer and pushes pH back up within days. Bring alkalinity into the 80-100 ppm range first and pH will hold longer.
Can I use baking soda to raise pool pH?
Baking soda (sodium bicarbonate) mainly raises total alkalinity, not pH. To raise pH specifically, use sodium carbonate (soda ash). Add it in small doses, 6 oz per 10,000 gallons raises pH roughly 0.2 points.
Is it safe to swim with high pH water?
Swimming in water above 7.8 won't immediately harm you, but your chlorine becomes nearly inactive. A pool at pH 8.0 has only about 21% of its chlorine working as a sanitizer, leaving the water undertreated even if the chlorine reading looks fine.
Need professional help in San Diego County?
Splash Pro Pools provides every service in this post. Call for a free quote.