Mythbusters: Pool Chlorine Edition

Many pool owners and even seasoned techs still cling to habits that feel safe but drain profits and create unstable water. The most common is the weekly “shock and pray” routine. A pool doesn’t need shock because the calendar says so; it needs it when free chlorine falls below the level required by cyanuric acid. Using Bob Lowry’s guideline, free chlorine should hover around 7.5% of CYA. That means a pool at 100 ppm CYA must hold roughly 7.5 ppm free chlorine to stay sanitary. When the reading dips, shock can help, but the target isn’t arbitrary. Breakpoint chlorination, combined chlorine removal, and bather load call for different levels. Mindless dosing wastes product and masks bigger issues like poor filtration or inadequate circulation. Balance first, then calculate the right rise in chlorine to hit the goal without overshooting.

The idea that “all chlorine is the same” causes more headaches than green walls. Trichlor, cal hypo, and liquid chlorine sanitize, but their byproducts and strengths vary. Trichlor is slow-dissolving, highly concentrated, and adds CYA with every tab—great for steady feed, terrible for rapid recovery. Cal hypo raises calcium as it delivers a strong punch; handy for quick lifts but risky in already hard water. Liquid chlorine adds salt and gives precise, immediate control without stacking stabilizer. Knowing these differences lets pros pick the right tool for a specific job: trichlor for maintenance in hot, sunny climates with dilution; liquid for daily trim and breakpoint; cal hypo when you need a fast surge and calcium allows. Treat them like different fuels, not interchangeable bottles.

High CYA is a hidden trap. Yes, a skilled tech can keep a pool at 150 to 200 ppm CYA clear by pushing chlorine higher. But the higher the CYA, the more chlorine you need to maintain an effective kill rate, and the slower pathogens die. Commercial codes often cap CYA at 100 ppm for this reason. In dry climates with little rain or no partial drains, tabs alone creep CYA upward until the pool becomes sluggish and expensive to maintain. A combined approach works better: use trichlor for steady feed, then support with liquid or cal hypo to meet daily demand without chasing higher and higher tablet counts. When dilution is scarce, plan partial drains or water exchange to reset stabilizer before summer peaks.

Algaecides started as an easy insurance policy, but they’re not a substitute for proper sanitation. Routine copper or quat adds can hide weak chlorine, dirty filters, and poor circulation. Today’s “enhancers” like borates, phosphate removers, and enzyme blends are smarter aids, reducing nutrient load and suppressing growth between weekly visits. Still, they work best in a system that already meets FC/CYA targets and maintains clean filters and good brushing habits. Think of enhancers as a buffer against heat waves, storms, and heavy use, not as a cure for chronic neglect. When algae shows up, check chlorine first, verify CYA, confirm flow and filter health, and only then consider support chemicals.

Saltwater generators deserve a reality check. They don’t replace chlorine; they make it. A salt system is a small, on-site factory converting chloride into free chlorine continuously, which smooths daily swings and reduces manual handling. That steady feed can be the most consistent form of chlorination available for residential care. But the same principles apply: you still need the right CYA, still target the FC/CYA ratio, still clean cells, and still watch pH and alkalinity as aeration can drive pH upward. Saying a salt pool is “chlorine-free” confuses owners and leads to lax testing. Educate clients that salt is a delivery method, not a different sanitizer.

If you manage a route, the lesson is simple: stop following a clock and start following the chemistry. Test accurately, set FC based on CYA, pick the chlorine form that fits the moment, and use enhancers strategically rather than by habit. Build dilution into your seasonal plan to control stabilizer, and reserve shock for when the numbers call for it or after events that drive demand. This balanced, evidence-based approach lowers total chemical use, prevents mid-summer spirals, and saves time that would otherwise be lost fighting preventable algae blooms.