Print Version: Tech Talk: Superchlorination Follow-up

Tech Talk: Superchlorination Follow-up

The Pumproom Press has heard from a small number of our members concerning the "phantom chloramine" discussion, and a few more experiencing the un-breakable combined-chlorine phenomenon. Most have commented on the existence of the problem rather than the solution.

Investigation with technical advisors of test-kit companies yielded less than desirable results, with one exception. Dr. Neil Lowry, our PPOA Canadian Advisor from Toronto who represents Taylor Chemical Company in Canada, commiserates; he's recommending a change in testing procedures and test kits. He tends to agree with us that the colorometric comparitors are harder to read with accuracy and repeatability, the related reagents aren't really as compound specific as we'd like them to be, and, especially with bromine, the color precipitants we view in the dosed sample tend to develop (change) over time. Using the relatively new FAS (that's ferros ammonium sulfate) titration kits, many of these problems are overcome. Here we measure a value by counting drops needed for a color shift or a bleaching, rather than trying to match a color's hue or its intensity. Each drop can represent .2 ppm or .5 ppm, accurate even for higher residuals. Especially for these higher values-like two, three, even five or more parts per million where small color variations and intensity shifts are impossible to discern – the drop-counting pool operator has a renewed confidence in his residual values.

No one has yet put her or his finger on the elevated but non-offensive "phantom" chloramine. We know that potassium monopersulfate will elevate DPD #3 artificially, showing up as the very thing that oxy-stuff is being used to eliminate. And sodium persulfate, also in the non-chlorine-shock family, fakes out the test kit similarly. (But, as it doesn't activate sodium bromide, it is less common in public pools.) Otherwise – while we suspect there is something – no other constituent of treated water has the reputation of pretending to be chloramine. Test kits, again, are more suspect than chemicals, showing depressed free or elevated combined readings.

Now that most of our busy pools are automated, scrutinizing and demanding more hair-splitting "precision" (you know about precision, don't you...), maybe a leading-edge test kit is the answer.

So what does this "FAS" kit solve? It appears that "free" and total values of chlorine will be more accurate, tending therefore to make the combined calculation equally more real. You'll then become more confident in your superchlorination targets. And, following the reasoning and procedures described in PrP #9, you indoor pool guys might actually get breakpoint chlorination to "break"! You'll recall that falling short of reaching that magic point on the initial attempt is the primary cause for making it very much more difficult on the next. It behooves us to get it done right on the first shot!

Reviewing a bit more, failed superchlorination actually creates those nasty compounds – products of incomplete oxidation – that don't succumb to our simplistic times-ten rules. These compounds, most of which are lumped under the name trihalomethanes or haloforms, are the chloro-unmentionables which are both more offensive and so much more difficult to get rid of. TTHMs, "total trihalomethanes", are organic, dominated by chloroform (see PrP #5 and PrP #7) which can be absorbed through the skin. While many THMs are unavoidable to a small degree, is ever so much better to do everything you can to keep them down than allowing conditions which create THMs – then having to get rid of them!

If superchlorination seems not to work, even with accurate targeting and copious air flushing, you may well need to begin a dilution process as a last resort. Common in Europe (see below), routine "blowdown" of indoor pool water may find its way into our practice in the US – especially now that pool loading is up and air handling is tighter than ever.

Preferring to know cause, effect and remedy rather than a lot of technical and chemical talk leading to no fix – most of us eventually say "just tell me what to do to make it all go away!" It's boiling down to this: Cause: Too many swimmers... Effect: Organic chloramines that won't go away... Remedy: Careful testing, generous, skilled superchlorination, maybe dilution...

As a postscript, there may yet be a chemical answer. Dr. Lowry tells PrP of a "new" Austrian two-part product... The first additive, a poly-aluminum chloride (PAC) called Hydrosan, is used before the filter as a microfloc of organic products. Water returning to the pool is then treated with a chemical called Hydrosan, which apparently produces ClO2 (chlorine dioxide). This powerful oxidizer/sanitizer, unlike HOCl, "does not chlorinate organic molecules" (make chlorinated organic amines). ClO2, heretofore somewhat risky to generate on site, promises to help us avoid those pesky chloramines.

~kw