Why is my pool so dirty!!!

[chem geek]

The problem is that most people in the pool industry -- stores, SWG manufacturers, even ORP controller manufacturers -- do not know or understand the relationship between CYA and FC (technical details of this relationship have been fortunately hidden away in The China Shop at this thread). There HAVE been articles written about chlorine's lower effectiveness in the presence of CYA, such as this one by the Professional Pool Operators of America (PPOA), but after my talking with a bunch of ORP sensor manufacturers and the manufacturer of Trichlor and Dichlor, I found that the manufacturer of Trichlor and Dichlor (Oxy -- Occidental Petroleum) was the only one with a clear knowledge and understanding of the chemistry involved based on scientific measurements made in 1973 and that were referred to on PDF page 18 (page 12 on the bottom of the page) of this EPA document. Even so, it seemed that I had worked out the details in a spreadsheet a little more clearly than those at Oxy had done, and in a presentation they made to the National Spa and Pool Institute (NPSI) in 2004 (NSPI appears to have gone away, at least in the U.S., and has been replaced by The Association of Pool and Spa Professionals, APSP), they (in my opinion) incorrectly used "averages" to make the point that only a minimum FC of 3 was needed in the presence of up to even 100 ppm CYA. They justified this by showing that out of a set of pools with varying FC and CYA, that the AVERAGE FC of pools with no algae was 3 or higher while the AVERAGE FC of pools with algae was below 3 and that even at 100 ppm CYA that minimum disinfection standards (i.e. 650 mV ORP) were met at 3 ppm FC. Of course, anyone who knows statistics knows that this is not the right way to get the right answer. The amount of CYA and FC varied in both sets of pools so some pools without algae had less than 3 ppm FC (and probably less than 30 ppm CYA) while others had more than 3 ppm FC (and possibly more than 30 ppm CYA). Also, just because a pool does not have algae does not mean that it COULDN'T have algae at that FC level -- the pool could have even been using a weekly algaecide. Finally, though it is true that 3 ppm FC with 100 ppm CYA is around 650 mV ORP and just sufficient for disinfection, this level of chlorine is NOT enough to prevent even run-of-the-mill green algae from developing. Of course, for the algae to ACTUALLY develop, it requires 1) the presence of algae cells (usually blown in from wind and leaves), 2) the presence of nutrients including carbonates (lots of those in the pool), nitrates and phosphates (often blown in from fertilizer) or silicates (not usually found in pools), 3) sunlight, 4) dissolved oxygen, 5) water (duh!) and 6) an absence of anything that would kill it such as sufficient levels of chlorine or an algaecide.

The bottom line is that the pool and spa industry as a whole is motivated by profit and there isn't much profit in having everyone use the cheapest store-bought chemicals (i.e. bleach, Borax, Baking Soda) and never having any problems with algae. I don't think that most pool store owners think that way, but nevertheless enough critical mass of manufacturers and some pool store owners do at least "not want to know" the truth if that would mean less profits. Of course, there really is plenty of money to be made by actually helping customers build and maintain pools and sell and repair equipment, but apparently the ability to sell even more chemicals is just too tempting. At least that is my opinion of the situtation.

By the way, do you brush the sides and bottom of your pool regularly, say weekly or every other week? I'm just curious as this seems to be another variable factor in determining the liklihood of developing algae. Apparently preventing biofilms from developing on pool surfaces may require less chlorine to kill the remaining free-floating algae.

[EDIT] I sent a detailed E-mail with many links to Goldline Controls suggesting, among other things, that they recommend a minimum FC level of 3 ppm (or even higher) with their 70-80 (where they say 80 is recommended) ppm CYA. I have also brought up other issues such as lower TA levels to reduce the rise in pH (they recommend 80-120 which is too broad a range -- should be 80-90). I also mentioned different salt cell designs with more plate area that could operate at lower CYA efficiently and referred to incidents of higher corrosion of coping/hardscape and metal (stainless steel poles in the pool and copper in heat exchangers) and possible ways of mitigating that problem or at least mentioning its possibility. These are all issues we have discussed at length in this forum (mostly in The China Shop). We'll see what they have to say. [END-EDIT]

Richard