Dealing with itchy eyes and cloudy water usually leads back to one question: what causes high ph in swimming pools and how do you stop it from happening every single week? If you've spent any time maintaining a pool, you know that keeping that pH level between 7.4 and 7.6 feels like trying to balance a plate on a stick while riding a unicycle. It's a constant battle against chemistry, nature, and the people using the pool.
When your pH levels start climbing north of 7.8, your chlorine loses its "muscle." It's still in the water, but it's essentially on vacation, refusing to kill off bacteria or algae. This leaves you with a pool that looks dull and feels uncomfortable. To keep things under control, you first need to look at the usual suspects behind those rising numbers.
The Salt Cell Factor
If you have a salt water pool, you probably love the soft feel of the water and the fact that you don't have to lug heavy jugs of chlorine around. However, salt water chlorinators are one of the most common answers to what causes high ph in swimming pools.
The way these systems work is through a process called electrolysis. As the salt water passes through the cell, it creates chlorine gas, but it also creates a byproduct called sodium hydroxide. Sodium hydroxide has an extremely high pH—we're talking way up at the top of the scale. As the generator runs to keep your chlorine levels up, it's constantly dripping this high-pH byproduct into your water. It's a bit of a trade-off; you get easy chlorine production, but you'll likely find yourself adding muriatic acid or dry acid more often than someone with a traditional chlorine pool.
Aeration and Bubbles
It sounds a bit strange, but bubbles are actually a major driver of high pH. Whether it's a fancy waterfall, a deck jet, or just a bunch of kids splashing around during a birthday party, aeration raises pH.
Here's the science without getting too "textbook" about it: your pool water contains dissolved carbon dioxide (CO2). When the water is agitated—like when it goes over a waterfall or gets stirred up by a fountain—it allows that CO2 to "off-gas" into the air. Think of it like a bottle of soda. When you shake it or leave it open, the carbonation escapes and the liquid changes. In a pool, as CO2 leaves the water, the pH naturally rises. If you have your water features running 24/7, you're essentially forcing your pH to climb every single hour.
The Type of Chlorine You Use
Not all chlorine is created equal. If you use liquid chlorine (sodium hypochlorite), you're adding a substance that has a pH of around 13. While it's great for a quick shock or regular maintenance because it doesn't add stabilizer (CYA) to the water, it does have a tendency to nudge your pH upward over time.
On the flip side, people who use "pucks" or tablets (Trichlor) often find their pH dropping because those tablets are very acidic. But if you've recently switched from tablets to liquid chlorine or a salt system, you'll suddenly notice your pH levels spiking in a way they never did before. Understanding this shift is key to managing your water balance.
New Pool Plaster
If you just finished a pool build or a resurfacing project, congratulations! But also, get ready to buy acid in bulk. New pool plaster is highly alkaline. For the first few months (and sometimes up to a year), the plaster is undergoing a curing process where it leaches calcium hydroxide into the water.
This process is a massive contributor to what causes high ph in swimming pools during that first season. You might find yourself testing the water and seeing a bright purple or deep red result on your test kit almost every day. It's annoying, but it's a normal part of the plaster "settling in." During this phase, you have to stay on top of it, or you'll end up with calcium scale sticking to your beautiful new finish.
High Total Alkalinity
You can think of Total Alkalinity as the "anchor" or the "bodyguard" for your pH. If your alkalinity is in the right range (usually 80-120 ppm), it helps keep your pH stable. However, if your alkalinity is too high, it will constantly pull your pH up with it.
When you have high alkalinity, it's very difficult to get the pH to stay down. You might add acid, see the pH drop for a few hours, and then watch it bounce right back up the next morning. This is often called "pH rebound." Until you lower the total alkalinity of the water, you're going to keep fighting the same battle. Usually, this involves a cycle of adding acid to lower both levels and then aerating the water to bring the pH back up while leaving the alkalinity at its new, lower spot.
Environmental Factors and "Fill" Water
Sometimes the problem isn't what you're doing to the pool, but what's coming into it. If you live in an area with "hard" water, your tap water might already have a high pH and high alkalinity. Every time you top off the pool after a hot week of evaporation, you're essentially "dosing" the pool with high-pH water.
Even the weather plays a role. Heavy rain can sometimes change pH levels, though usually, rain is slightly acidic and might lower it. However, the runoff from your deck or garden that washes into the pool after a storm can carry minerals and debris that mess with the balance. Even something as simple as a sudden algae bloom can cause a spike. As algae grows, it consumes CO2 (just like the aeration process we talked about earlier), which naturally drives the pH up.
Why Should You Care?
It might seem like a lot of work to keep that number in check, but the consequences of ignoring it are a headache. When pH is high, your water gets cloudy because the calcium in the water starts to "fall out" of solution. You'll see white, crusty deposits on your tiles and inside your pipes.
More importantly, your swimmers won't be happy. High pH changes the way the water interacts with human skin and eyes, leading to that classic "burning eye" sensation that people often wrongly blame on "too much chlorine." In reality, it's often just the pH being out of whack. Plus, because the chlorine isn't working efficiently at a high pH, you're essentially wasting money every time you add chemicals.
Wrapping It Up
At the end of the day, knowing what causes high ph in swimming pools is half the battle. Whether it's your salt cell working overtime, the kids playing with the fountains, or just the natural curing of your new plaster, there's always a reason for the rise.
The best advice? Get a good test kit—the kind with the drops, not just the strips—and check your levels at least twice a week. Once you get a feel for how your specific pool reacts to things like rain or heavy use, you'll be able to predict the spikes before they turn your water cloudy. A little bit of acid here and there is a lot cheaper and easier than trying to scrub scale off your tiles or fighting a mid-summer algae breakout. Keep that pH in the sweet spot, and your pool will be the clear, inviting oasis it's supposed to be.