Chlorine's pH impact in swimming pools (w/ Terry Arko)

If you've been in the pool industry for any length of time, chances are you've been told that liquid chlorine has a "high pH" that needs to be balanced with muriatic acid. This practice has been passed down through generations of pool professionals like gospel truth. But what if everything you've been taught about chlorine and pH is wrong?

In a recent episode of the Rule Your Pool podcast, host Eric Knight sits down with chlorine expert Terry Arko to dissect this pervasive industry myth and reveal what's really happening when you add chlorine to your pool. The conversation uncovers decades of misunderstanding and provides the scientific clarity that every pool professional needs.

The Industry Myth: A Legacy of Blind Following

Terry Arko's introduction to pool chemistry in the late 1970s perfectly illustrates how misinformation spreads through the industry. His experience reveals a troubling pattern that persists today.

One of the first things they told me when I got to a pool and it was getting to chemicals and this was not even had nothing to do with even testing pH, the chlorine, anything. It was just that you're going to put a gallon of this liquid in let's say a gallon per 10,000 gallons and for every gallon of this liquid in you have to put a quart of acid in. That's what I was told.

— Terry Arko, Rule Your Pool Podcast

When Arko questioned this practice, seeking to understand the reasoning behind it, he was told something that should alarm every professional: "don't ask why just do it. It's the way it's been done." This mentality has created a cascade of misunderstanding that continues to influence pool maintenance practices decades later.

The "rule" evolved over time, with newer professionals being taught to add smaller amounts of acid—Eric Knight mentions being taught to add 16 ounces per gallon of liquid chlorine in 2016, half of what Arko was originally taught. But the fundamental misunderstanding remained the same.

What Really Happens When Chlorine Meets Water

To understand why the traditional approach is flawed, we need to examine the actual chemical reactions occurring when liquid chlorine (sodium hypochlorite) is added to pool water. The process involves multiple steps that most pool professionals have never learned.

When sodium hypochlorite dissolves in water, it immediately creates two compounds: hypochlorous acid (HOCl) and sodium hydroxide. The sodium hydroxide is indeed a strong base that temporarily raises the pH—this is where the original observation came from. However, this is only the beginning of the story.

The hypochlorous acid produced in this reaction serves a crucial purpose—it's the actual disinfecting agent that kills bacteria, viruses, and algae in your pool. Interestingly, this same compound is what our own white blood cells produce to fight infections in our bodies, making it one of the safest and most natural disinfectants available.

The Self-Neutralizing Truth About Chlorine

Here's where the chemistry gets fascinating and where decades of industry practice have been based on incomplete understanding. That hypochlorous acid doesn't just sit in the water—it actively works to disinfect and oxidize contaminants. As it does this work, something remarkable happens.

What happens once you have chlorine in the water is it's going to kill or it's going to oxidize or it's going to get broken down by sunlight and it doesn't matter which happens to it because either way that hocl becomes hcl hydrochloric acid... the amount of hydrochloric acid produced is almost almost identical to the amount of sodium hydroxide produced.

— Eric Knight, Rule Your Pool Podcast

This revelation changes everything. The hydrochloric acid (muriatic acid) produced naturally by the chlorine's disinfection process effectively neutralizes the sodium hydroxide that caused the initial pH spike. In essence, chlorine produces its own acid to balance itself out—no external acid addition required.

Terry Arko confirms this understanding, explaining that this creates what chemists call an equilibrium reaction, where the pH naturally balances out as the chlorine does its job.

When Acid Addition Might Actually Be Harmful

Not only is the traditional practice of adding acid after liquid chlorine unnecessary, but it can actually be counterproductive and even dangerous in certain situations. The timing and reasoning behind any acid addition should be completely different from what many professionals have been taught.

If you're going to lower pH in a pool, it should be done before adding chlorine, and the decision should be based on the pool's existing pH level—not on the fact that you're adding liquid chlorine. There's also a critical safety consideration that many pool professionals aren't aware of.

The last thing you want to do is pour chlorine on top of where you just poured acid... because you will basically create a very harmful gas... in a pool it's diluted pretty quickly right if you were to pour them together in a bucket you would create a very harmful gas called mustard gas... it's what they used in world war one to kill people.

— Terry Arko, Rule Your Pool Podcast

This safety concern alone should make every pool professional reconsider their chemical addition practices. The proper approach is to test the water, determine if pH adjustment is actually needed based on the pool's current chemistry, and if so, add acid first, wait several minutes, then add chlorine.

The Real-World Implications

Terry's experience in Southern California provides a perfect example of how coincidence can be mistaken for causality. His pools maintained good pH levels despite following the incorrect industry practices, but this was due to other factors in his specific situation—hard water conditions and the use of trichlor tablets that naturally lower pH.

This experience highlights a crucial point: just because a practice seems to work doesn't mean it's correct or optimal. Many pool professionals may have good results while following flawed practices due to other variables in their specific situations.

The implications of understanding chlorine's true behavior extend beyond just chemical addition practices. It affects how we think about pool chemistry balance, equipment selection, and troubleshooting water quality issues. When we understand that liquid chlorine is essentially pH neutral once it completes its disinfection work, we can make more informed decisions about water balance and chemical management.

Practical Applications for Pool Professionals

Armed with this correct understanding of chlorine chemistry, pool professionals can adopt more effective practices:

• Test pH independently of chlorine additions and adjust only when the actual pH reading indicates it's necessary
• Understand that temporary pH spikes after adding liquid chlorine will self-correct as the chlorine does its work
• Focus on maintaining proper alkalinity levels to establish the right pH ceiling rather than constantly fighting pH with acid additions
• Separate acid and chlorine additions by time and space for safety reasons
• Base chemical adjustments on water testing results, not on assumptions about product behavior

The episode also touches on how this understanding applies to other types of chlorine products, each with their own pH characteristics. Calcium hypochlorite, dichlor, trichlor, and salt chlorine generators all behave differently, but the fundamental principle remains: understand the complete chemical process, not just the initial reaction.

Breaking Free from Industry Dogma

This discussion about chlorine and pH represents a larger issue within the pool industry—the tendency to follow practices without understanding the underlying science. Terry Arko's early experience of being told "don't ask why, just do it" reflects a culture that prioritizes tradition over truth.

The most successful pool professionals are those who question conventional wisdom and seek to understand the science behind their practices. This episode serves as a perfect example of how industry "common knowledge" can be fundamentally flawed and how proper education can lead to better results and safer practices.

As the industry continues to evolve, with new technologies and better understanding of water chemistry, it's crucial that professionals remain open to learning and updating their practices. The goal should always be optimal water quality achieved through the most efficient and safe methods possible.

Understanding the true nature of chlorine's behavior in pool water isn't just about debunking myths—it's about providing better service to customers while working more efficiently and safely. When we stop adding unnecessary acid to pools, we reduce chemical costs, minimize pH fluctuations, and eliminate the safety risks associated with mixing acids and chlorine.

The conversation between Eric Knight and Terry Arko represents the kind of educational content that can transform industry practices. By sharing scientific knowledge and questioning long-held assumptions, pool professionals can elevate their expertise and provide better outcomes for their customers. After all, the goal isn't just to maintain pools—it's to understand the chemistry well enough to optimize water quality while minimizing chemical use and maximizing safety.

Episode Chapters

• 00:00 Introduction and Industry Myths
• 05:30 Terry's Early Pool Career Experience
• 12:15 The Chemistry Behind Liquid Chlorine
• 18:45 Why Chlorine is Self-Neutralizing
• 25:20 Safety Concerns with Acid Addition
• 32:10 Practical Applications for Pool Pros