How to Adjust pH in Pool: The Chemistry Behind Crystal Clear Water

I've been maintaining pools for over fifteen years, and if there's one thing that separates a sparkling oasis from a cloudy mess, it's understanding pH. Not just checking it mindlessly with test strips, but really grasping what's happening in that water on a molecular level.

pH adjustment isn't rocket science, but it's also not as simple as dumping chemicals and hoping for the best. I learned this the hard way when I first started – turned a neighbor's pool into what looked like a giant glass of milk because I got overzealous with the soda ash. That was an expensive lesson.

The Sweet Spot Nobody Talks About

Everyone knows pools should be between 7.2 and 7.8 pH, with 7.4-7.6 being ideal. What they don't tell you is that your pool has a personality. Some pools naturally drift acidic, others climb toward alkaline like they're trying to escape. This depends on everything from your water source to what kind of sanitizer you use, even the type of plaster or liner.

My own pool, for instance, loves to creep up to 7.8 no matter what I do. I've accepted this about it, like accepting that your old truck pulls slightly to the left. Fighting your pool's natural tendencies is like swimming upstream – exhausting and ultimately futile.

The real trick is understanding why pH matters. It's not just about comfort, though nobody enjoys swimming in water that stings their eyes. pH affects how well your chlorine works. At pH 7.0, your chlorine is about 75% effective. Bump that up to 8.0, and you're down to 20% effectiveness. That's why high pH pools often struggle with algae despite having "enough" chlorine.

Reading Your Water Like Tea Leaves

Testing is where most pool owners go wrong. They dip a test strip, glance at the colors, and call it good. But proper testing requires patience and technique.

First off, those test strips? They're fine for a quick check, but for accurate pH adjustment, you need a proper test kit with reagents. The phenol red test is your friend here. When I test, I always rinse the comparator tube three times with pool water before taking my sample. Take the water from elbow-deep, away from returns and skimmers. The surface water lies to you.

Here's something most people miss: test your pH at the same time each day. pH naturally rises during the day as carbon dioxide off-gasses. Testing at 8 AM versus 4 PM can show wildly different results. I always test mid-morning, after the sun's been on the pool for a couple hours but before the afternoon heat really kicks in.

The Lowering Game

When your pH climbs too high – and it will, especially in areas with hard water – you need to bring it down. Muriatic acid is the go-to, though dry acid (sodium bisulfate) works too if you're squeamish about handling liquid acid.

With muriatic acid, less is more. I've seen too many pool owners dump in half a gallon because they want immediate results. Your pool isn't a chemistry experiment; it's a living system that needs time to equilibrate.

My method: calculate how much acid you need (roughly 10 ounces of muriatic acid per 10,000 gallons to drop pH by 0.2), then add only 75% of that amount. Why? Because it's easier to add more than to correct an overshoot. Pour the acid slowly into the deep end with the pump running, walking around the perimeter as you pour. Never pour it all in one spot – I've seen that etch plaster faster than you can say "warranty void."

The real secret is pre-dilution. Fill a 5-gallon bucket halfway with pool water, add your acid to the bucket (never the reverse – remember "acid to water, just like you oughta"), then pour this mixture around the pool. It's gentler on your surfaces and disperses more evenly.

Raising pH Without Raising Everything Else

Low pH is less common but more problematic. Acidic water is hungry – it wants to dissolve things. Your plaster, your equipment, your sanity.

Soda ash (sodium carbonate) is the standard pH increaser, but here's where it gets tricky. Soda ash significantly raises total alkalinity along with pH. If your alkalinity is already high, you're creating a new problem while solving the old one.

This is where I sometimes break from conventional wisdom. For small pH adjustments when alkalinity is already adequate, I'll use borax. Yes, the laundry stuff. It raises pH with minimal impact on alkalinity. About 1/2 box per 10,000 gallons raises pH by 0.2. Just make sure you get plain borax, not the detergent kind.

When using soda ash, dissolve it first. I mean really dissolve it – in a bucket of warm water, stirring until you can't see a single grain. Undissolved soda ash creates those mysterious white clouds that make your pool look haunted. Broadcast the solution evenly around the pool with the pump running.

The Alkalinity Connection

You can't talk about pH without discussing total alkalinity. Think of alkalinity as pH's bodyguard – it prevents rapid pH swings. Low alkalinity means your pH bounces around like a pinball. High alkalinity makes pH stubborn and hard to adjust.

The relationship is delicate. When I need to lower both pH and alkalinity, I use muriatic acid but apply it differently. Instead of walking around the pool, I pour it slowly in one spot with the pump off. This creates a column of low pH water that eats away at the alkalinity. After an hour, I turn the pump on to circulate. It's like precision surgery instead of a sledgehammer.

Raising alkalinity without significantly affecting pH requires sodium bicarbonate (baking soda). The pool store will sell you "alkalinity increaser" for three times the price, but it's the same stuff. About 1.5 pounds per 10,000 gallons raises alkalinity by 10 ppm.

The Forgotten Factor: Aeration

Here's something that took me years to fully appreciate: aeration naturally raises pH without affecting alkalinity. Every waterfall, fountain, or spillover is slowly pushing your pH upward by driving out carbon dioxide.

I had a client with a gorgeous vanishing edge pool who couldn't understand why his pH kept climbing despite perfect alkalinity. Turned out, that vanishing edge was basically a giant pH-raising machine. We solved it by running the edge feature only when needed for aesthetics, not 24/7.

You can use this to your advantage. Need to raise pH but alkalinity is already high? Run your fountains, point your returns upward to create surface agitation, or even use an air compressor to bubble air through the water. It's slow but effective, and completely chemical-free.

Timing Is Everything

When you add chemicals matters almost as much as what you add. Never adjust pH right before swimmers arrive – give it at least 4 hours for muriatic acid, 2 hours for soda ash. I prefer evening additions when possible. The chemicals have all night to circulate and integrate without UV degradation or swimmer interference.

Also, never adjust pH and chlorine simultaneously. High pH makes chlorine less effective, but freshly added chlorine can give false pH readings. I follow a simple pattern: test and adjust pH in the morning, shock or chlorinate in the evening.

Weather plays a role too. After heavy rain, pH usually drops from the slightly acidic rainwater. During drought conditions with lots of fill water additions, pH tends to climb. Anticipating these changes means fewer emergency adjustments.

The Long Game

Perfect pH isn't about hitting 7.4 once and calling it done. It's about understanding your pool's rhythms and working with them. My pool naturally rises about 0.2 pH per week during summer. Instead of constantly adding acid, I let it drift from 7.2 to 7.6, then bring it back down. The average stays perfect, and I'm not living with a test kit in my hand.

Keep records. I know it sounds tedious, but a simple notebook tracking your tests and chemical additions reveals patterns. After a season, you'll know exactly how your pool behaves and can anticipate problems before they develop.

One final thought: pool chemistry is forgiving. Unless you're wildly off, a pH of 7.1 or 7.7 won't ruin your swim. The pool police won't show up. What matters is consistency and avoiding extremes. I've seen too many pool owners chase perfect numbers and create more problems than they solve.

The best pool is one you enjoy, not one that keeps you up at night worrying about decimal points. Master the basics of pH adjustment, understand your pool's tendencies, and you'll spend more time swimming and less time testing. That's the real goal, isn't it?

Authoritative Sources:

Taylor Technologies. Pool & Spa Water Chemistry: A Testing and Treatment Guide. Taylor Technologies Inc., 2019.

Lowry, Robert W. Pool Chemistry for Service Pros: A Guide to Understanding the Principles of Water Chemistry Maintenance. Lowry Consulting Group, 2018.

National Swimming Pool Foundation. Pool & Spa Operator Handbook. National Swimming Pool Foundation, 2020.

Tamminen, Terry. The Ultimate Guide to Pool Maintenance. 3rd ed., McGraw-Hill, 2007.

Williams, Roy D. Complete Guide to Pool Care: Everything You Need to Know to Keep Your Pool Sparkling Clean. Creative Homeowner, 2021.