CYA for Salt Chlorinator Pools II

[chem geek]

I understand Richard,

It just seems very odd to me. I'm an architect, and contrary to public perception that we're all about making things look nice, our first and foremost task is ensuring public safety. As is that of every other professional that works in constructing/managing the built environment. It just seems too odd that this particular part of the built environment is somehow exempt from that goal.

The manufacturers recommend keeping the FC at 3.0 or higher and that this is OK to do for CYA up to 70 and they say you shouldn't go above 100. So from a disinfection point of view at normal pH (7.5), even at 100 ppm CYA the HOCl is 0.012 which is a minimum for disinfection that roughly corresponds to an ORP near 650 mV which is the same level that commercial pools use as a minimum. So the issue is not one of health safety, at least for easy-to-moderate-to-kill bugs (i.e. up to E.coli), but of having sparkling clean pools without algae. Now some in the industry claim that this 3 ppm rate will also prevent algae, but Ben's table and real-world results dispute this (except, perhaps, for SWG pools where the jury is still out on the exact chlorine level needed to prevent algae in such pools).

The study I looked at done by one manufacturer, however, used statistical averages to prove their point saying that the average chlorine level in a group of pools (with varying amounts of CYA) without algae was 3 while in a group of pools with algae the average was below 3. That is, of course, not the right way to look at data. It should be the maximum chlorine level (actually HOCl level) in the pools with algae that is a starting point for analysis. The minimum chlorine level in the pools without algae is also useful and these will likely overlap due to "lucky" pools without enough chlorine but that haven't yet developed algae. Of course, algae growth depends on lots of other factors including nutrients in the pool, sun exposure, rate of introduction of algae into the pool, etc.

So I do not believe that the manufacturers are trying to skirt public safety. My analogy with the tobacco companies was again facetious and way too extreme. A better analogy might be drug companies who promote their solutions rather than non-patentable alternatives that sometimes work as well or better. Also, it could just be that the manufacturers just aren't being as careful with their studies, not intentionally, but just based on who did the study -- these aren't scientifically peer-reviewed articles, but industry conference presentations (the O'Brien paper, on the other hand, was done scientifically with university professors and may have had peer-review).

Richard