For good measure: paying attention to the ppm only and ignoring ORP may be putting your patrons at risk.(TECH TALK)(oxidation reduction potential research)

For the past 16 years, I have been traveling around the United States training operators. During that time, one thing has become abundantly clear: There's a lot of confusion about the relationship--and the difference between--oxidation reduction potential and parts per million.

Part of the problem is that many state health departments don't regulate ORE but they do regulate ppm. So operators tend to focus on ppm and forget about ORP. That's a mistake.

When it comes to maintaining healthy pool water, ORP is actually more important than ppm. What's more, relying on ppm readings alone can provide a false, and dangerous, sense of security.

To understand why, we have to start with basic water chemistry. When chlorine is added to water, a chemical reaction occurs between chlorine and the water, called hydrolysis. During hydrolysis, chlorine reacts rapidly with water to form two separate chemicals: hypochlorus acid (HOCl) and hydrochloric acid (HCl).

Of these two compounds, the important one is hypochlorus acid, or HOCl. This compound is the "active form" of chlorine, providing the needed oxidation, substitution and disinfection reactions. Without getting too technical, you want significant HOCl in the pool water for effective oxidation and disinfection.

However, ppm and HOCl do not always correspond. That's because HOCl dissociates or separates into two components, the hydrogen ion (H+) and the hypochlorite ion (OCl-). Like the hydrolysis reaction, the degree of dissociation is primarily dependent on temperature and the pH of the water. As the pH goes up (a shift to the right), the hypochlorite concentration increases. As the pH goes down (a shift to the left), the hypochlorus concentration is increased.

Therefore, while your test kit may show ample amounts of chlorine at a pH 7.8, which is within most health ...