COMMON MYTHS in Pool-Water Chemistry, Part 1

How many of these do you come across each day at the pool?

1. There’s too much chlorine in the pool; you can smell it!
No, no, no; this familiar cry of the swim-team mom is the most common error of all relating to pool sanitation. The truth is, when you smell it, that’s not chlorine! There’s been too little chlorine in the pool for days, during which ammonia-type introductions occurred. This urine, sweat and decomposing organic matter produces ammonia compounds of chlorine, commonly called chloramines – the source of the odor and irritation. The good stuff, active free chlorine (HOCl), has neither odor nor irritating qualities. You usually can keep this active oxidizer and sanitizer busy maintaining the pool’s clarity and sanitation, while actually avoiding the chloramine development, by carefully holding a higher, not lower, residual of free chlorine.

2. Shocking the pool is necessary each week.
We hope not! The term “shock” is a back-yard-pool expression, relating to blind overchlorination on a periodic basis. This is often a useless, waste of chlorine. On the other hand, superchlorination, calculated to reach chemical breakpoint to eliminate existing chloramine, is necessary when it’s necessary; that is, it’s needed when these ammonia compounds have been allowed to develop.

3. Pool-water balance is comprised of proper values of chlorine and pH.
No, chlorine has nothing to do with “balance”, while pH, temperature, total alkalinity, calcium hardness and, to a minute degree, total dissolved solids make up the group of five variables commonly used to calculate the Calcium Saturation Index (CSI). This numerical index is often used as the prime indicator of the water’s so-called balance. The CSI helps an operator predict her or his water’s aggressiveness, its scaling potential, or the state of balance between those extremes. “Chlorine,” is simply the necessary oxidizer/sanitizer compound one adds to the nicely balanced water.

4. High Total Dissolved Solids (TDS) makes water dull or even cloudy, and significantly reduces chlorine’s work value.
Emphatically false. TDS values well in excess of 2000 ppm, indeed in excess of 20,000 ppm, have no influence whatsoever on clarity. This is most easily exemplified by seawater at the Great Barrier Reef or near Mexico’s Cozumel, where divers commonly observe visibilities of 200 feet or more. High TDS? You bet. Open ocean water has a dissolved-solids value near 34,000 ppm, mostly salt – which is the dominant dissolved compound in your mature pool, too. Chlorine’s function as an oxidizer or a sanitizer is virtually unaffected by TDS; electronic sanitizer control and pH management work just fine even in the sea-water pools found in coastal resorts and on cruise ships.