Freelancer said:
Richard that is a truly excellent answer and was exactly what I was looking for.
:
"The chlorine kill time would be such that cross infection between bathers was a real concern".
:
Oh just so that you know that neither of the links to the poolforum appear to be working.
I'm glad that BBB is working out for you and that you were able to convince others through sound chemical advice and practical demonstrable experience that it works.
So how do you maintain the FC levels in your pools without getting CYA to rise? I assume you don't visit your pools more than once a week, do you? Are you using chlorinating liquid (or bleach) with wide swings of FC, but at the higher 80 ppm CYA to minimize chlorine loss from sunlight? Did the pools mostly have pool covers that lowered the rate of chlorine breakdown from sunlight? I'm just curious since we get the question from pool service companies for how to do BBB when you only visit a pool once a week and we don't have great answers for that other than automated systems (peristaltic pump or The Liquidator) or big FC swings or use of some Trihclor tabs with additional dilution and supplemental weekly FC shocking (kind of a hybrid approach), or using a supplemental algaecide weekly such as PolyQuat 60.
As for kill times, keep in mind that the pool industry uses the "real pools" argument to say that these laboratory kill times don't apply to real pools. There are even some early studies that seemed to show this, but when I looked at them in more detail I noticed that their FC levels were very low (often < 0.5 ppm) and the bather loads high (commercial/public pools) so that it was quite possible the FC got used up combining with ammonia to form monochloramine which is then a reasonably effective algicide and a slower killer of bacteria (though roughly the same as 1 ppm FC with 50 ppm CYA). So that could have helped prevent algae growth and also made kill times independent of CYA level (the kill times were slow, though still fast enough to prevent uncontrolled growth, but seemed to be mostly independent of CYA level). Another argument is what I like to call the "well, nobody died" argument that goes something like the "[no] disease outbreak" phrase used in ANSI/APSP-11 under "Effect of Cyanuric Acid on Chlorine Kill Rates" that may have been put in at the urging of the head of the APSP-11 committee who worked for Chemtura (BioLab, BioGuard, SpaGuard, OMNI, etc.):
The effect of cyanuric acid on oxidation of organics, kill rates of bacteria and viruses, algae, and protozoa has been demonstrated. Some authorities or standards have suggested adjusting the required chlorine residual to the concentration of cyanuric acid to compensate for the reduction in rates of kill. These studies are not fully comprehensive and applicability to real pools has not been demonstrated. Specifically, we do not have any empirical evidence that a disease outbreak has been linked to a particular cyanuric acid level in a properly sanitized pool (i.e., when at least 1 ppm free available chlorine was present in the pool).
As with most deceit, it isn't that the above statements are untrue, but I consider the conclusions to be misleading. An outbreak requires enough people to get sick such that there are enough of them to report to their doctors and enough of those doctors to report to their health department. So you generally need some serious uncontrolled bacteria growth before something this extensive is going to occur (Crypto is another matter, but even normal chlorine levels don't inactivate that protozoan oocyst much at all). An increase in transmission from person-to-person is unlikely to show up as an "outbreak" if just a few people near the one sick person also get sick. Also, the Pinellas County, Florida study had 49 out of 486 pools with no chlorine at all and about half of these had high bacterial counts indicating uncontrolled bacterial growth yet there were presumably no "outbreaks" of illness so there isn't a 1-to-1 of uncontrolled bacteria growth with illness.
The PoolForum links work OK for me so try them again; is anyone else having the problem of accessing
The PoolForum?
Richard