Pool chlorine is primarily made through electrolysis of salt water to create sodium hypochlorite (liquid chlorine) or by combining chlorine gas with lime to make calcium hypochlorite (powder/tablets).
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Pool chlorine is manufactured through two main industrial processes: liquid chlorine (sodium hypochlorite) is made by electrolyzing salt water, while chlorine tablets and powder (calcium hypochlorite) are produced by reacting chlorine gas with lime. Understanding these processes helps pool owners make informed decisions about which chlorine type works best for their situation.
Liquid chlorine, chemically known as sodium hypochlorite, is the most common form used by professional pool technicians and follows the TFP method recommendations. The manufacturing process is surprisingly straightforward:
The primary method involves electrolyzing a solution of salt water (sodium chloride brine). When an electric current passes through the salt water solution, it splits the molecules and recombines them into sodium hypochlorite, hydrogen gas, and sodium hydroxide. This process occurs in large industrial electrolytic cells containing titanium electrodes.
The chemical reaction is: NaCl + H₂O → NaOCl + H₂ + NaOH
Commercial liquid chlorine typically contains 10-12.5% available chlorine, making it highly effective for pool sanitization. This is why many pool professionals prefer liquid chlorine over store-bought "pool shock" - it's essentially the same product used in municipal water treatment.
Calcium hypochlorite (cal-hypo) tablets and powder undergo a more complex manufacturing process that involves handling dangerous chlorine gas.
First, manufacturers produce chlorine gas through the electrolysis of salt water, but instead of creating the final product directly, they capture the chlorine gas separately. This chlorine gas is then reacted with slaked lime (calcium hydroxide) in large reaction vessels under controlled conditions.
The reaction produces calcium hypochlorite: Cl₂ + Ca(OH)₂ → Ca(OCl)₂ + H₂O
For tablet production, the resulting calcium hypochlorite powder is mixed with stabilizers, binders, and sometimes cyanuric acid (CYA), then compressed into tablet form. This is why tablets often contain built-in stabilizer - it's added during manufacturing.
Trichlor tablets (trichloroisocyanuric acid) are made through a different process involving cyanuric acid. Manufacturers react cyanuric acid with chlorine gas under specific temperature and pressure conditions. This creates tablets that are about 90% available chlorine but also add CYA to your pool with every dose.
Important note: This is why TFP methodology recommends careful monitoring of CYA levels when using trichlor tablets, as excessive CYA buildup can make your chlorine less effective.
Your salt water chlorine generator essentially mimics the industrial liquid chlorine manufacturing process on a smaller scale. When you add salt to your pool and run the generator, it electrolyzes the salt water to produce sodium hypochlorite directly in your pool.
The process generates the same sodium hypochlorite as commercial liquid chlorine, but at much lower concentrations (typically 3-6 ppm). This is why salt water pools still require proper water balance - you're still using chlorine, just producing it on-site.
Commercial chlorine manufacturers must maintain strict quality control because pool owners depend on consistent available chlorine levels. Liquid chlorine is tested for:
This quality control is why purchasing chlorine from pool supply stores or having it delivered from pool service companies often provides more consistent results than big-box store alternatives.
Understanding manufacturing helps explain why proper storage matters. Liquid chlorine naturally degrades over time, losing about 50% potency after 6 months in ideal storage conditions. Heat and sunlight accelerate this process because they reverse the electrolytic process that created the sodium hypochlorite.
Calcium hypochlorite tablets and powder are more stable because they're in solid form, but they're also more dangerous to handle due to their concentrated nature and potential for explosive reactions with organic materials.
Modern chlorine manufacturing has become more environmentally conscious. Many facilities now capture and reuse the hydrogen gas produced during electrolysis, and some use renewable energy sources to power the electrolytic process. The sodium hydroxide byproduct is often sold to other industries, reducing waste.
Safety reminder: Never attempt to manufacture chlorine at home. The industrial processes involve high voltages, dangerous gases, and require specialized equipment and safety protocols.
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