Re: Chlorine/CYA Chart
thepoolpros.com said:
Im not sure the relavence of this chart. the key is to protect the chlorine that you put into the pool. 10 ppm of cyanuaric acid will protect 1.5 ppm of chlorine from the UV destruction of the Chlorine Molecule. The 1/2 life of Chlorine when unprotected is 1 hour. By adding stabilizer it will greatly decrease your cost to operate your swimming pool.
So if you want to keep 10ppm of Cl2 in your pool, you should have a cyanuaric level of atleast 70 ppm. Because of the added benefits as an algacide and ph buffer i recommend to keep the stabilizer as high as possible. In Florida with concrete or gunite pools, I recommend a stabilizer of atleast 100ppm and a max lmit of 400ppm.
I wrote a piece about this on my website.
I'm sorry, but it doesn't work at all the way you described. CYA is not an algaecide -- if it were, you wouldn't have literally hundreds of pool owners coming to this site with algae problems in their pools every year when their CYA levels get high and they don't maintain an appropriately high FC level for that CYA level. If you want an additional pH buffer, use 50 ppm Borates (and they are also a mild algaecide).
There is a chemical relationship between chlorine and CYA that has been known definitively since at least 1974 as described in this paper. CYA protects chlorine from breakdown from the UV in sunlight in two ways. First, most of the chlorine combines with CYA to form compounds (called chlorinated isocyanurates) that are resistant to breakdown from UV -- they do breakdown, but more slowly. Second, the CYA itself can absorb UV to somewhat shield lower depths, though this is a secondary and less dramatic effect (though is still noticeable in many pools as one gets towards 80 ppm CYA). Unfortunately, chlorine combined with CYA is for practical purposes not a sanitizer or oxidizer so it is only the small amount of unbound chlorine that does all the work to kill pathogens and prevent algae growth.
I don't understand your recommendation to keep the CYA level at least at 100 and no more than 400 ppm in light of your article on
Chlorine Lock where you state "Do not keep your stabilizer, cyanuric acid, levels above 100 parts per million because it will stop the chlorine from working and turn your pool green." You also state that "10 ppm of cyanuric acid will protect 1.5 ppm of chlorine from UV destruction for a period of about 10-14 days with minimal outside contamination" which is complete hogwash. If you only have 10 ppm CYA in the water, 1.5 ppm FC will breakdown from the UV in sunlight quickly -- not half lost in an hour, but still cut in half in a few hours such that there is no way it will last for 10-14 days (see Table 1 in
this link where the chlorine concentration is cut in half in about 3 hours at 10 ppm CYA; at 25 ppm CYA it is cut in half in around 7 hours and note that this is at pH 7 while at higher pH the loss would be faster due to more hypochlorite ion, OCl
-, that degrades faster than hypochlorous acid, HOCl). Chlorine also gets used up in other ways other than sunlight so would get to zero long before 10-14 days.
On that same Chlorine Lock page you write "it has been proven that cyanuric levels of up to 400 ppm and higher increases the disinfection powers of chlorine in swimming pool water. the reasoning is that in swimming pool water, there is the presence of ammonia which when combined with Chlorine, or cyanuric acid actually , slightly, magnifies the disinfection properties of chlorine, NOT LOWER IT, OR STOP IT." Where is the scientific evidence for this? You are right that at high CYA levels the chlorine oxidation of monochloramine takes longer so its levels can build up (to disastrous results as described in
this paper), but this only occurs if there is ammonia in the pool such as from bather waste. Also, it takes much higher levels of monochloramine to be as effective as chlorine. The bottom line is that higher CYA levels reduce the active chlorine concentration to significantly slow down the killing of pathogens and the killing of algae. You shouldn't count on having ammonia in the water to form monochloramine as any sort of backup!
Since you are an NSPF CPO instructor, I suggest you read the
Certified Pool Operator (CPO) training -- What is not taught thread. Note that there are many links to scientific sources that document what is really happening.
Richard