Center for Disease Control & Swimming Pools

[lbridges]

1st - not sure this is the right place, so move if appropriate.

And I apologize if this has been discussed and I missed it, but I found reading the CDC page on residential pools interesting - and as a bonus it includes the sources for their conclusions.

I don't understand their table 14.4 and values for combined chlorine, but overall it seemed a reasonably accurate and balanced document - even from a TFP perspective.

 

[Jersey Devil]

Pretty complete. The flaw I see is that there is no published relationship between CYA level and required FC. The recommended FC levels are are essentially fixed. There is a recommended 100 ppm max for CYA buried in a table, but no reference to the continued build-up of CYA resulting from the use of stabilized chlorines. Considering that this is a guide for residential pools, it is likely that homeowners and even pool service providers would assume that there is no potential problem in this regard. I remember that Chem Geek had been active in communicating these concerns to the CDC or other appropriate agency. It would save a lot of people a lot of trouble if this were addressed outside of TFP.

 

[tim_pool_newbie]

Great article...thanks for posting. I've printed it out to include in my pool book, and read in a bit more detail later. But one thing I learned while quickly skimming was that apparently calcium hypochlorite works best in cold water pools and does not work well in heated pools or spas. Interesting!

 

[JasonLion]

That is a nice document overall, especially their coverage of a wide variety of topics, but it is full of minor errors and potentially misleading statements. Overall the worst problem is the inconsistent level of detail. Some sections are very detailed, while other more important things are left out completely. Their tables of recommended levels are missing crucial items and then cover things like iodine, which almost no one uses. If you tried to follow this as you primary reference you will have problems.

A few of the more obvious problems:
"The ideal pH to avoid eye irritation is 7.3." Only true when CYA is zero.
"A typical-use pool should have a pump and filtration system capable of pumping the entire contents of the pool though the filters every 6 hours." This is a common requirement for commercial pools, but doesn't apply to residential pools. Following this will result in higher equipment and electrical costs.
In the "Disinfection" section, they don't say what CYA levels they assume. The numbers are obviously not true if CYA is 100. I suspect they are only true when CYA is zero. Yet lower down they recommend CYA be at least 10.
Table 14.1 - what could they be thinking on the "Bluish green color" line, that looks like a recipe for creating more serious problems to me. This table is also very inconsistent in it's level of detail.
Table 14.2 is only true when CYA is zero. With CYA it is way off.
Table 14.3 lists the PH effects of adding each kind of chlorine is misleading at best. They fail to take into account the effect of the chlorine getting consumed, which is acidic, so real world effect will not be as indicated.
Table 14.4 combined chlorine numbers are simply wrong. Plus many factors are listed that are optional, for example iodine. And some lines are labeled as chlorine, while others actually refer to chlorine even though they are not labeled that way (for example wading pools). And what is going on with the Bromine line?
Table 14.5 it would appear we should have both bromine and chlorine at the same time? Obviously misleading. "Dissolved solids" promotes the usual nonsense about TDS, simply not true.