Bob Lowry on Pool Service Rookie Mistakes

New pool service pros often inherit “rules” like keeping free chlorine at 2–4 ppm and calling it good, then wonder why algae keeps coming back. A core mistake is not understanding how cyanuric acid (CYA) changes chlorine strength. With CYA in the water, most chlorine becomes bound and only a small fraction is immediately active as sanitizing hypochlorous acid (HOCl). Add in the way pH shifts HOCl versus OCl-, and the effective killing power can drop fast. That is why a pool can test “high chlorine” and still grow algae. If you run a pool service business, this is one of the most important pool chemistry concepts for consistent, algae-free results and fewer emergency cleanups.

Once you accept that the active sanitizer is what matters, the free chlorine target has to scale with CYA. The practical field rule discussed is simple: keep free chlorine at about 7.5% of the cyanuric acid level to prevent algae. So if CYA is 100 ppm, free chlorine needs to be about 7.5 ppm, not 3 ppm. This reframes troubleshooting: a trichlor pool with CYA of 150–200 ppm and free chlorine of 5–6 ppm can still be under-sanitized relative to its stabilizer level. This CYA to free chlorine ratio approach is easier than doing detailed equilibrium math on every stop, and it helps pool technicians explain results to customers in plain language.

Borates also come up as a tool for algae prevention and water feel. When borates are maintained around 50 ppm, the chlorine requirement can be lowered from 7.5% of CYA to roughly 5% in many cases, making targets more manageable while still maintaining protection. That said, extremely high CYA still creates unrealistic chlorine demands, so the long-term fix is often controlling stabilizer buildup, not just “adding more products.” For service pros, the operational win is fewer recurring algae calls, less reliance on weekly shock routines, and clearer accountability: if CYA is high, either chlorine must rise with it or CYA must come down.

Another rookie mistake is ignoring water balance tools like the Langelier Saturation Index (LSI). LSI helps predict whether water is scale forming, corrosive, or balanced by considering factors such as pH, alkalinity, calcium hardness, temperature, total dissolved solids, and modern additions like CYA and borates. But there’s a deeper point: “balanced” does not always mean “stable.” You can hit an LSI number with a high alkalinity and low pH combination that looks fine on paper but drifts quickly, creating constant pH rise and ongoing adjustment. Targets and stability-focused ranges reduce surprises between visits, protect plaster and equipment, and keep service routes predictable.

Finally, filtration runtime is a real-world driver of clarity that chemistry alone cannot fix. Turnover is based on pool volume and flow rate, and one turnover only captures about 65% filtration, while three turnovers can reach roughly 92–95%. If a customer cuts runtime to save power, they may not even achieve one turnover, leading to cloudy water and dead zones with poor circulation. Worse, with long periods of no circulation, localized algae or biofilm can consume chlorine in one area without fresh sanitizer moving in. For pool maintenance, the best results come from pairing correct sanitizer targets with sufficient circulation and verified flow, so the water stays clear all week, not just right after service.