What are chlorides?

If you've ever wondered what happens to all that chlorine you add to your pool, you're not alone. While most pool owners focus on maintaining proper chlorine levels for sanitation, few understand the invisible byproducts left behind after chlorine does its job. These byproducts, called chlorides, are accumulating in your pool water right now—and understanding them is crucial for proper pool maintenance and equipment longevity.

Understanding Chlorine vs. Chlorides: The Chemistry Behind Your Pool

To grasp what chlorides are, we need to start with basic chemistry and the periodic table. Chlorine belongs to a group called halogen gases, alongside fluorine and bromine. But here's where it gets interesting—chlorine doesn't naturally exist alone.

If you ever see chlorine, like elemental chlorine as we say, it's a Cl2. Kind of like elemental oxygen is also O2 because an O1 is unstable... Anything in nature is going to look for balance.

— Eric Knight, Rule Your Pool Podcast

The key difference lies in electrical charge. Chlorine atoms can exist in different states:

• Chlorine (Cl+): Positively charged, actively seeks electrons, can oxidize and disinfect
• Chloride (Cl-): Negatively charged, has extra electrons, cannot oxidize or disinfect

Think of chlorine as the active worker and chloride as the retired byproduct. When chlorine does its job—killing bacteria or oxidizing contaminants—it transforms from the active chlorine into the inert chloride.

How Your Pool Creates Its Own Muriatic Acid

Here's a fascinating process happening in your pool that most people never realize. When you add chlorine products, they form hypochlorous acid (HOCl)—the active sanitizer. But when HOCl oxidizes something, it undergoes a chemical transformation:

When that splits apart and dissociates in water, you're going to get chlorides. Chlorides are left behind by all types of chlorine because of this process. Chlorine dissolves. It becomes HOCl. It then gets reduced when it kills or oxidizes into HCl, which, by the way, is why liquid chlorine and calhypo are net neutral pH or very close to it after they do their job.

— Eric Knight, Rule Your Pool Podcast

This means your pool is constantly creating hydrochloric acid (muriatic acid) and chloride ions. It's a natural part of the sanitization process, explaining why chlorine products eventually reach pH equilibrium despite their initial pH levels.

The Inert Nature of Chlorides—With One Important Exception

The good news about chlorides is that they're largely harmless. They don't corrode most materials, they don't interfere with water balance, and they don't pose health risks. However, there's one significant exception that can cost pool owners thousands of dollars: stainless steel.

Chlorides are inert unless they're in the presence of stainless steel. And the reason for that is stainless steel has a chromium oxide layer with something called molybendam in it... this chromium oxide layer in particular gets affected and interfered with by chlorides.

— Eric Knight, Rule Your Pool Podcast

Stainless steel's corrosion resistance comes from a protective chromium oxide layer. Chlorides interfere with this protective barrier, making the steel vulnerable to corrosion. This is why you might see orange rust spots on stainless steel fixtures in pools, especially indoor facilities.

Interestingly, chlorides themselves don't directly cause corrosion—they can't take electrons from metals. Instead, they compromise the steel's natural protection, allowing other factors to cause the actual corrosion.

The Chloramine Connection: Why Indoor Pools Face Unique Challenges

Indoor pools face a particularly challenging situation with chlorides. The problem starts with chloramines—those notorious compounds that cause eye irritation and that distinctive "pool smell." But there's more to the story than most people realize.

Nitrogen trichloride sounds like it would have chloride ions in it. But if you look at the valences of them, they actually have chlorine in them in a plus one state... What's happening is the chlorine in the trichloramine is oxidizing the metal. And when it does that, it gets reduced into hydrochloric acid, again, just like chlorine, creates its own muriatic, which further accelerates the corrosion.

— Eric Knight, Rule Your Pool Podcast

This creates a double-whammy effect in indoor pools:

1. Chloramines in the air condense on metal surfaces
2. The active chlorine in chloramines oxidizes the metal
3. This creates hydrochloric acid, accelerating corrosion
4. The process leaves behind chlorides that interfere with stainless steel's protective layer

This explains why indoor pool facilities often struggle with corroded ventilation systems, light fixtures, and other metal components.

Managing Chloride Levels in Your Pool

Since every chlorine product eventually breaks down into chlorides, these compounds accumulate over time in your pool. They show up in conductivity tests and contribute to your Total Dissolved Solids (TDS) readings.

For most pools, chloride accumulation isn't problematic until levels become extremely high. However, salt water pools face unique considerations:

• Salt chlorine generators may struggle with excessive TDS levels
• Many manufacturers recommend keeping TDS below 4,500 ppm
• Higher chloride levels can interfere with the electrolysis process

Unfortunately, there are only two ways to remove chlorides from pool water:

• Reverse osmosis filtration: Expensive but effective for severe cases
• Drain and dilute: Partial water replacement to reduce concentration

Prevention focuses on proper water balance maintenance and avoiding over-chlorination, which minimizes unnecessary chloride buildup.

Practical Implications for Pool Owners and Operators

Understanding chlorides helps explain several common pool phenomena:

Why chlorine products eventually reach pH neutral: The formation of hydrochloric acid during the oxidation process naturally brings down pH, explaining why liquid chlorine and cal-hypo don't permanently raise pH despite their initial alkaline nature.

Why stainless steel components fail prematurely: Chloride accumulation, especially in indoor environments, compromises the protective chromium oxide layer on stainless steel.

Why salt water pools require TDS monitoring: Excessive chlorides can interfere with the electrolytic cell's ability to generate chlorine effectively.

Why proper ventilation is crucial indoors: Preventing chloramine condensation on surfaces reduces both the direct corrosive effects and chloride accumulation on metal components.

Key Takeaways for Pool Maintenance

The science of chlorides reveals important truths about pool chemistry that every pool professional should understand. While chlorides are largely inert and harmless, their interaction with stainless steel and accumulation over time can create real maintenance challenges.

For daily operations, focus on maintaining proper water balance to minimize unnecessary chlorine consumption and chloride formation. Pay special attention to stainless steel components, especially in indoor facilities where chloramine condensation can accelerate problems.

Most importantly, remember that chloride accumulation is inevitable—it's a natural byproduct of the sanitization process. Regular water testing, proper ventilation (for indoor pools), and occasional dilution when TDS levels climb too high will help maintain optimal pool conditions while protecting your equipment investment.

Understanding the difference between active chlorine and inert chlorides isn't just academic—it's practical knowledge that can save money on equipment replacement and help you maintain better water quality for swimmers.

Episode Chapters

• 00:00 Introduction to Chlorides
• 05:30 Understanding Halogens and Chemical Balance
• 08:15 Chlorine vs Chloride Valences
• 12:45 How Chlorine Creates Muriatic Acid
• 16:20 Why Chlorides Are Inert (Except With Stainless Steel)
• 19:10 Chloramines and Metal Corrosion
• 24:30 Managing Chloride Levels
• 27:45 Practical Implications and Course Information