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Why recurring water quality problems are rarely chemical — and why no dosing regime can compensate for poor hydraulics, undersized filtration, or contaminated drainage.
Most discussions of swimming pool water quality revolve around chemistry. Pool operators routinely measure pH, residual chlorine, total alkalinity, calcium hardness and cyanuric acid, then decide what chemicals need to be added. That information is freely available in books and across the internet.
Our objective is different. Rather than explaining how to correct water chemistry, we explain the engineering prerequisites required to make water chemistry work at all.
In our experience, recurring water quality problems are rarely caused by poor chemistry. They are caused by poor hydraulics, inadequate filtration and compromised circulation. Until these are corrected, chemical treatment addresses the symptom while the root cause remains untouched.
A heavy shower passes. The water turns green. The water is tested — high pH, low residual chlorine, poor oxidation. Acid is dosed. Chlorine is added. In severe cases, the pool is superchlorinated or gassed.
The chemistry was treated. The engineering was not.
See the operating numbers this engineering is built to hold →
The most common site error is deck drainage sloped toward the pool. During rainfall, mud, dust, leaves and organic matter wash directly into the overflow channel and enter the circulation system.
The filtration plant is then expected to remove contamination that should never have entered the pool in the first place. The same deck channel, badly built, is also the fourth point of origin in leak diagnosis →
No dosing regime can compensate for a deck that drains into the pool.
Chemistry works only if chemicals reach every litre of water. Common causes of broken distribution:
Field Note
We have inspected institutional pools where the main drain became the de facto circulation point — because operating the overflow system would have pushed the pool past its permissible operating level. The plant kept running. The distribution collapsed. Some areas of the pool received fresh, disinfected water; others received almost none.
Water chemistry can only work when every litre of water is continuously circulated, filtered and mixed.
The most persistent confusion in pool engineering. A faster turnover does not produce clearer water. Effective filtration depends on adequate filter surface area, correct filtration velocity, sufficient media depth, and proper hydraulic balancing.
Larger filters require larger plant rooms. Where plant room space is compromised →, filters are reduced in size while larger pumps are installed to hold the turnover figure. The turnover time appears satisfactory. The filtration quality does not. The result is poorer particulate removal, greater chemical consumption and declining water clarity.
Once these engineering deficiencies exist, the symptoms begin to appear. They are not the root causes. They are merely the consequences.
| What You See | What It Actually Is |
|---|---|
| Green water after rainfall | Deck drainage washing contamination into the overflow channel |
| Persistent algae growth and biofilm on walls | Dead zones — treated water never reaches those areas |
| Eye and skin irritation, chloramine odour | Localised excess chlorine reacting with ammonia from bathers — a distribution problem |
| Rising chemical consumption | An undersized filter compensating chemically for what it cannot remove physically |
| Water splashing from overflow channels | Poorly levelled channel construction |
| Declining water clarity despite correct readings | Excessive filtration velocity — the water passes through too fast to be polished |
Chloramine odour has a name and a number — see Combined Chlorine on Operating Standards →
A Properly Engineered Pool Provides
When these fundamentals are correct, maintaining water chemistry becomes significantly easier, safer and more economical.
At Premium Pools, we begin with the physics of water. When the engineering is right, the chemistry follows.
Before a single chemical dose is calculated, filtration determines how much particulate load the water carries. The chart below shows how particulate removal efficiency falls as filtration velocity increases, and how glass media outperforms silica sand at every velocity band.
Particulate removal efficiency vs. filtration velocity — glass media vs. silica sand. Hover over the chart for exact readings.
Sand-curve shape and the 25 m/h threshold reflect PWTAG's published filtration rate guidance (low-rate ≤10 m/h, medium-rate 10–25 m/h, high-rate 25–50 m/h; high-rate ≈10–25% as effective as medium-rate). Source: pwtag.org. Glass-media curve reflects directional industry consensus on finer particle capture, not a single controlled study.
Cartridge filters typically capture particles down to 10–20 microns — finer than sand (20–40 microns), coarser than glass (3–10 microns). Shown as a single reference value, not a velocity curve: cartridge systems use a much larger surface area at a fundamentally different, lower flux rate than sand or glass beds, and PWTAG does not publish an efficiency-vs-velocity relationship for them.