Filtration – Foundation of Safety for Your Pool
Water disinfection is the foundation of safety for your pool.
But it’s not a single factor — it’s a system of parameters working together. The effectiveness of disinfection depends directly on pH, water temperature, contamination levels, and pool usage.
The most common disinfectant is chlorine. In a pool, there are two types of chlorine:
Free (active) chlorine: Cleans water and kills microbes. Recommended level: 1.5–3 ppm.
Combined chlorine (chloramines): Spent “waste” chlorine. Useless, causes strong odors, and irritates eyes. Acceptable level: up to 0.2 ppm.
This fundamental difference explains why one pool smells like chlorine while another does not.
Free Chlorine (HOCl)
Free chlorine is the “active fighter.” It floats in the water waiting for bacteria or viruses. When it encounters a pathogen, it oxidizes it and destroys itself in the process.
A strong chlorine smell is a signal that water needs adjustment, not an indicator of cleanliness.
Combined Chlorine (Chloramines)
This is a byproduct. When free chlorine reacts with organic matter (sweat, urea, cosmetics), it forms chloramines.
Chloramines cause red eyes, itchy skin, and the sharp chlorine odor. To remove them, pools undergo “shock treatment,” rapidly raising the free chlorine level to literally burn off the spent chlorine.
Cyanuric Acid (CYA): The Stabilizer
CYA is often called “sunscreen for chlorine.”
Ultraviolet light breaks down chlorine molecules. Without a stabilizer, sunlight can destroy all disinfectant in an outdoor pool in just a few hours, leaving the water unprotected.
CYA molecules form a temporary weak bond with chlorine, shielding it from sunlight while still releasing it to kill pathogens when needed.
The ideal range is 30–50 ppm. At this level, there is a balance between protecting chlorine from the sun and maintaining its effectiveness in water.
Chlorine Lock: Hidden Loss of Disinfection Efficiency
Chlorine lock is a common issue in private pools.
CYA does not evaporate or break down. It accumulates when using stabilized chlorine such as tablets or granules.
As CYA rises, the proportion of active chlorine (HOCl) responsible for disinfection decreases. Chlorine is present and measurable, but it works much weaker.
Even at normal or high chlorine levels, water may lose sanitary safety and start to turn green. This is called chlorine lock — a situation where chlorine exists but its effectiveness is significantly reduced.
Using Trichlor (Tablets and Granules)
Trichlor is convenient but requires careful monitoring.
It contains stabilized chlorine (trichloroisocyanuric acid) with CYA. Regular use gradually increases CYA. Without monitoring, this reduces disinfection efficiency.
Trichlor has a low pH of around 2.8. Constant use without adjustment can lower pool pH, affecting water balance and equipment.
How to Reduce Excess Cyanuric Acid
Unlike pH or chlorine, CYA levels cannot be adjusted with chemicals.
The only effective way to lower CYA is to drain part of the water and replace it with fresh water without stabilizer, or perform a full water replacement depending on test results.
Regular measurement of CYA is critical. Without it, pool maintenance becomes uncontrollable.
Excess CYA (80–100 ppm) significantly reduces chlorine activity, and very high levels (150–200 ppm) almost completely block disinfection, making the water unsafe for swimmers.
Effect of CYA on Total Alkalinity (TA)
High CYA levels can cause total alkalinity (TA) readings to appear elevated. Part of this alkalinity comes from CYA itself, not the actual buffer components of water.
As a result, test results may look normal, but the water may struggle to maintain stable pH.
In simple terms, numbers on a test may seem correct, but they do not always reflect the real condition of the water.
Conclusion
Disinfection effectiveness depends not just on chlorine levels but on the conditions in which it operates. Without controlling CYA, even normal chlorine readings can be misleading.
Water parameters work together like ingredients in a recipe: proportions matter as much as the ingredients themselves. Even one parameter out of balance can change the overall result.