The Importance of Proper pH Balance
One of the most important steps in keeping water clear and safe for swimmers is maintaining a proper pH level. It is also a critical step in maximizing sanitizer efficacy to prevent damage to pool surfaces and equipment.
The Basics of pH
pH is a scale of how acidic or basic (alkaline) a substance is, with a pH of 0 being incredibly acidic (battery acid), and a pH of 14 being very basic (liquid drain cleaner). A substance is considered neutral when the pH is at 7, acidic when it's below 7, and basic when it's above 7. From a technical view, pH is a measure of how many hydrogen ions or hydroxide ions are in a solution. The more hydrogen ions in a solution, the more acidic it is, and the more hydroxide ions in a solution, the more basic it is.
A simple analogy can be drawn if we think of pH in terms of extremes. For this comparison, we'll call low pH "steam" and high pH "ice." We aren't comfortable in either a steamy or icy environment. Room temperature is similar to a neutral pH—and we want to make sure our environment, or our pool water, stays in that comfortable and safe range. When trying to balance pool water, a pH between 7.2 and 7.8 is the typical industry standard. If using a liquid chlorine or a calcium hypochlorite-based sanitizer, a pH range of 7.2-7.4 is preferred since these products will raise your pH over time. A range of up to 7.8 is appropriate when using products like Trichlor, which will lower your pH with use.
How pH Increases Chlorine Efficacy
Put simply, when cyanuric acid (CYA) is not present, pH controls the strength of the chlorine in your pool water, as determined by the amount of hypochlorous acid. Hypochlorous acid is the "active" chlorine that sanitizes and disinfects. When you put a chlorine sanitizer into your pool, it becomes a mixture of hypochlorous acid (HOCl) and hypochlorite ions (OCl-). The pH determines how much of each is present in your water. At a pH of around 7.5, there is a 50/50 mix of HOCl and OCl-. When the pH drifts up toward 8 or 9, the amount of hypochlorous acid drops significantly, while the amount of hypochlorite ions increases the same amount. And while OCl- will sanitize, it is 80 to 100 times less effective than HOCl. This means that as pH increases, the killing power of the chlorine in your pool falls off a cliff. Since everyone wants a clear pool, but also a healthy, disinfected pool, that typical pH range of 7.2 to 7.8 is essential.
If your pool uses Trichlor products, you'll want to keep chemicals to bring your pH back up handy—chemicals like sodium carbonate (soda ash). Conversely, if your pool uses hypochlorite-based products (bleach or calcium hypochlorite), a chemical to bring your pH back down will be necessary. Three common chemicals, muriatic acid, granular sodium bisulfate and carbon dioxide gas (CO2), are frequently used to adjust pH down. Another new technology, a sodium bisulfate tablet system, has been introduced recently and is gaining popularity because it is safer to use and easier to apply.
The Effects of pH
Keeping your pool's pH in the proper range protects your swimmers, the pool equipment, and the pool itself. A pH of 7.4 is "ideal" as it is the pH of our eyes and mucous membranes. If pH gets too high, swimmers can experience irritated skin and red eyes, along with damage to products like swim goggles. Furthermore, you may start to see calcium deposits on pool parts and equipment such as metal fixtures and tile. Those deposits can be worse inside your pipes and pump components, causing coated pipes and poor pump performance.
If the pH goes too low, eyes and skin will feel the effects, but corrosion is the biggest concern. Rust can form that may weaken metal fixtures or ladders, creating safety hazards. The water can also begin to eat away at pool plaster and grouting. While controlling your pool's pH is important for swimmer comfort and clear water, wandering out of the 7.2-7.8 range can cause lasting damage to your pool, swimming equipment and even pumps.
So, the next time you are testing your water, or instructing others to do so, keep in mind that pH is so much more than just a measurement in your test kit.
- Samantha Williams, Chemist II, Westlake Water Treatment Products