I have a post on Pool Water Chemistry in The China Shop that has some graphs based on the chemistry determined back in 1974 when the chlorine/CYA relationship was definitively determined. However, the graphs on CYA's protection of chlorine from breakdown from sunlight make assumptions that we have since found to be incorrect. Namely these graphs do not take into account that there is an additional CYA protection effect by shielding lower depths from UV -- not just from binding to chlorine to make it more stable. Also, the graphs I made on chlorine breakdown in sunlight use Kent Williams' data for the presumed rates of breakdown of chlorine bound to CYA from UV in sunlight and those rates may be incorrect.

I also have a link to an ORP post that shows the fallacy of using ORP for absolute measurements. It can be OK to use for process control to maintain an FC level by using an ORP mV "setpoint", but that's about all. (Ben, if you could allow the "CODE" to work again in vBulletin, that will make some formatting work better -- also, if vBulletin allows for subscripting and superscripting, that would be helpful as well).

I wrote E-mails to Kent Williams at PPOA in 2004, 2006 and 2007 and never received any response. My comments with regard to Kent Williams' paper and commercial pools are limited to his suggestions regarding the importance of supplemental oxidation due to the high bather loads in such pools and have nothing to do with the chlorine/CYA chart which applies to the chlorine levels needed to prevent algae in ALL pools. The oxidation of bather waste, particularly urea, can be very slow if there is no exposure to UV or higher water temperatures (i.e. spas). So indoor pools and high bather load pools can benefit from supplemental oxidation not only to oxidize faster but also to help prevent disinfection by-products (DBPs) which virtually every scientific paper shows to be mostly proportional to bather load. Though one could raise active chlorine levels (either raising FC or lowering CYA to raise ORP) for faster oxidation as he proposes, one could increase DBPs by doing so.

Richard