What Are the Side Effects of a Low pH Level in a Hot Tub?

When maintaining your hot tub, you want to create conditions that are hostile to bacteria but friendly to your guests and your equipment.

Disinfection

An acidic hot tub pH will detract from the quality of your hot tub experience.An acidic hot tub pH will detract from the quality of your hot tub experience.
That's why you need to control its pH level. A low or excessively acidic hot tub pH is just as undesirable as a high one. If your pH falls too low, you may start to observe a number of different effects.

Disinfectants like calcium hypochlorite actually become more effective at killing hot tub bacteria as the pH goes down, so an acidic pH will not hamper disinfection initially. The lifespan of the chlorine in the hot tub will decrease, however, because you lose chlorine to outgassing and degradation more rapidly at an acidic pH. Over time, chlorine levels in your hot tub will drop more rapidly. This effect is accentuated because the warm temperatures in your hot tub accelerate the breakdown of the chlorine in any case.

Corrosion

Low, or acidic, pH accelerates corrosion of metals like the pipes and equipment in your hot tub. Again, the temperature of the hot tub water accentuates the problem, because higher temperature accelerates chemical reactions like those that drive corrosion. This effect is especially undesirable because it shortens the lifespan of your equipment and may eventually necessitate costly repair or parts replacement.

Calcium Carbonate

Calcium carbonate becomes increasingly soluble at acidic pH levels. A common experiment in grade school involves placing a piece of limestone in hydrochloric acid; the limestone fizzles and reacts to form calcium chloride and carbon dioxide gas. The results in your hot tub are not quite so dramatic; nonetheless, a lower pH will retard scale formation. If the walls of your hot tub are made of calcium carbonate or similar materials, you will accelerate the rate at which they dissolve.

Swimmer Safety

A pH level below 7 may irritate your guests' eyes and skin, and the lower the pH drops, the more pronounced this effect will become. The ideal range for pH in your hot tub lies between 7.2 and 7.8, a pH level that promotes disinfection while avoiding the deleterious consequences of an over-acidic pH. Testing your hot tub pH frequently and correcting as necessary will help you avoid these kinds of problems.

About the Author

Based in San Diego, John Brennan has been writing about science and the environment since 2006. His articles have appeared in "Plenty," "San Diego Reader," "Santa Barbara Independent" and "East Bay Monthly." Brennan holds a Bachelor of Science in biology from the University of California, San Diego.