The TWELVE MOST COMMON MYTHS in Pool-Water Chemistry

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, simply 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 sea water at the Great Barrier Reef or near Mexico’s Cozumel, where visibilities of 200 feet or more are commonly observed by divers. 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 coastal resorts and on cruise ships.

5. The ideal pH for any pool water is 7.4.
Impossible to know. Out of context, there is no “ideal” anything. The water’s hardness and other CSI variables, even the values read from the make-up (fill) water, help you determine the most appropriate value. In general, the best pH is “the lowest pH you can get away with” as chlorine works much better at lower pH values. That actual number is, of course, clearly limited by the bottom of the state health-code ranges, and otherwise chosen by pool operators considering the influences and trends of their sanitizer and their make-up water – wisely keeping that CSI thing in balance all along. Curiously, a pH of 7.4 is not even legal in South Dakota where pH 7.6 is dictated, and almost never used in Germany (the birthplace of water-chemistry science) where their national code’s working range is 6.5 to 7.3! Typically, they hold 7.0 or 6.9.

6. Green hair in blondes is caused by too much chlorine.
Not at all. Green hair is caused by copper in the water – but not right away during a swim… Copper must precipitate as a green salt during a high-pH shampoo, usually long after the pool water has dried in the hair. Two errors, then: The operator had allowed copper (pipes, heater, impeller) to be dissolved by his excessively aggressive water. No problem yet – crystal clear water still. Error two is the swimmer’s fault; she or he didn’t shower (rinse) or even towel dry the pool-wet hair. It dried with that half cup of copper-bearing water leaving its contents behind. Then the high pH of a shampoo (pH 9 or higher), hours or days later, caused the precipitation of copper oxide (and maybe some sulfide). Everything from Aspirin to vinegar has been used to reduce the coloration after the fact, but prevention is the much better approach. The so-called swimmer’s shampoo is simply a lower pH product that doesn’t clean as well but keeps the hair below pH 8.3 where all the dissolved solids otherwise begin to fall out of solution. Everybody, by the way, gets green hair under this sequence of events; it just shows up better in bleached blondes.

7. Significant chlorine can be saved by adding a supplemental sanitizer or sanitizing device to the pool’s treatment system, such as a UV lamp or an ionizer.
Not true, since the amount of chlorine consumed by virtue of its sanitizing activity is so small it cannot be measured. Supplementing chlorine in its bug-killing job may be nice, but it is not particularly necessary or economical. UV and copper/silver ions are sanitizers only; while sometimes serving useful functions, they don’t oxidize – chlorine’s toughest job. (See item 8, below.) One chlorine compliment, ozone, on the other hand, sanitizes and oxidizes. Still, based on the type of ozone generator, its sizing and installation arrangement, little if any chlorine is saved.

8. Oxidizing and sanitizing are about equal burdens on the chlorine residual.
Not even close. Continuing with the explanation in 7, above, oxidizing (mostly burning up suspended organic particles) consumes much more chlorine than the related task of sanitizing. Losses to sunlight and other destruction or dissipation all exceed the tiny-but-effective amount used in making the water germ free. Help the chlorine in its oxidizing task, and minimize losses to sunlight, then there’s often money to be saved.

9. Cyanuric Acid (CYA) always makes chlorine last longer and it does not “lock” the chlorine up.
Neither is true all the time. While the silly phrase “chlorine lock” is not appropriate, the Oxidation-Reduction Potential (ORP), measured by electronic systems as the qualitative indicator of chlorine’s work value, is significantly reduced by the excess use of CYA stabilizer. This often happens progressively, accumulating CYA in the pool when using stabilized chlorine products (such as trichlor tablets) over long periods of time. (See PrP article, #7 page 3, or accessed through the cover page of the website.) CYA readings of 100 ppm or more can easily develop, with algae blooms and loss of clarity a strong possibility. The good news is that well managed cyanuric-acid residuals, generally in the 5 ppm to 20 ppm range, will significantly increase chlorine’s longevity while the trade-off loss in activity remains tolerable. Large outdoor pools in sunny climes can save thousands of dollars in chemicals when carefully stabilized. Stabilizers, (often called conditioners,) are inappropriate indoors as stabilization from sunlight destruction does not occur (chlorine losses remain the same) yet the ORP is nonetheless depressed resulting in less chlorine function.

10. High hardness makes cloudy, scaly water.
Nope; it takes a very high pH (well above your state’s code) to precipitate calcium scale. If you keep your pH reasonable -- we hope in the low sevens so your chlorine is producing serious ORP -- you can run your hardness up to 1000 ppm or even higher with brilliantly clear, non-scaling water. Even if the calcium saturation index is positive, such as +.5 to +1.5 (well into the so-called “scaling range”), your water will not scale at all unless the pH exceeds 8.0. Meanwhile a high-hardness CSI will minimize or eliminate metallic corrosion in those new, high-e heaters, where 500 ppm CH and higher are values routinely being recommended by suppliers and consultants.

11. When a DPD chlorine test flashes a little pink then turns crystal clear, your water has almost no chlorine in it.
The opposite is true! More spas are fried and bathing suits bleached because of this error than just about any other. As you know, the universally accepted DPD test for chlorine turns progressively more pink as higher residuals are encountered in the sample… that is until the indicator is itself reverts to a clear resultant. This phenomenon occurs somewhere near 20 ppm chlorine, the actual value varying with different pH or total alkalinity conditions. Many, many untrained operators or “helpers” have dumped excessive amounts of chlorine in their water (most often in hot whirlpools or spas), thinking all along that for some crazy reason they just hadn’t yet put enough in to get a reading! In a small body of water this testing error has resulted in a few hundred parts per million chlorine residual, creating some very unsafe, damaging or at least unpleasant conditions.

12. You can do an adequate and safe job as a public-pool operator without wasting time taking a certification course.
Please don’t try. Very good plumbers and top-rated mechanics have wrecked million-dollar pools in all parts of the country, thinking that tossing in a little chlorine while holding some good pH/chlorine test-kit readings will take care of that chemistry stuff just fine. Becoming “certified,” required by more and more health departments now, is essential. The training received from the National Recreation and Park Association’s Aquatic Facility Operator (AFO) course, the National Swimming Pool Institute’s Certified Pool Operator (CPO) program or the YMCA’s Pool Operator on Location (POOL) class (or any other recognized certification course) will give the prospective pool gal or guy the knowledge base upon which to build the necessary experience needed to safely and successfully care for and operate a modern public pool.

Obviously there’s much more be said on each of these topics. If you’re not a PPOA member, look into one of the certification courses mentioned in 12, above, then join us. If you’re already certified, check out the Professional Pool Operators of America’s site, www.ppoa.org, and consider being one of us.

~ kw

©2004 Professional Pool Operators of America