terryc said:
I understand how the binding of CYA to chlorine makes a large percentage of the FC ineffective. However, I'm not sold on the binding making the chlorine/CYA combination benign and non-harmful? Is that the case?
Read the "Chlorine/CYA Relationship" section in the thread
Certified Pool Operator (CPO) training -- What is not taught. You will see numerous links to peer-reviewed scientific studies in respected journals showing how chlorine bound to CYA is indeed far, far less reactive than unbound chlorine. It is not completely non-reactive, but is less reactive by at least a factor of 150 if not more. For disinfection and for reacting with negatively charged surfaces such as skin, it will be even less reactive than the factor of 150 because the dominant chemical species is negatively charged (HClCY
-). The chemistry is absolutely consistent with disinfection rates, inactivation rates, algae prevention (on the forum; the one scientific paper is an outlier), oxidation rates, and ORP. There is also virtually no skin absorption (based on CYA skin absorption studies). That thread is not new and if you spent time reading in the forum you would learn about these things -- as Dave (duraleigh) wrote, we've been at this for 6 years on this forum and with Ben Powell at
The PoolForum and
PoolSolutions for years before that where Ben started in 1997 (though had experience before that). This stuff isn't something we're pulling out of our, well, you know...
My wife also has personal experience of the difference CYA makes where she swam every year for 5 months in an indoor commercial swimming pool with 1-2 ppm FC and no CYA where her swimsuits would degrade over just one winter season (elasticity gets shot; occurs before fading since the suits are "chlorine resistant") and her skin gets flakier and hair frizzier. During the 7-month summer season she swam in our outdoor residential pool with 3-6 ppm FC and 40 ppm CYA and her swimsuits have lasted for around 7 or so years and the effects on her skin and hair are far less noticeable. The difference is so extreme that she now no longer swims in the commercial pool and instead we extend our season with expensive gas heating into the winter except for maybe 2 months.
terryc said:
From what I've read about the peroxymonosulfate it is pretty benign. The borate may be a little more questionable.
MPS itself is an oxidizer so will have some similar oxidative effects on swimsuits, skin and hair as chlorine and since it is not moderated in its strength by CYA some of its effects will be even stronger. It does not have a bleaching effect so its oxidative effects will be more like the elasticity changes, but quite frankly it's a selective oxidizer just like chlorine so will oxidize some things and not others and we know from spas using Nature
2 with MPS that you can't keep the water clear on that system by itself and need to use chlorine once a week or so. MPS does not produce chlorinated disinfection by-products and there is no evidence of it producing products that are mutagenic, genotoxic or carcinogenic of which I am aware. By itself, it is not a disinfectant, but at hot temperatures along with silver ions it can kill pathogens quickly so is approved by the EPA in the Nature
2/MPS system for spas only.
As for borates, read
Are Borates Safe to Use?
As for chlorine overall, the quantity of disinfection by-products in outdoor residential pools that are typically low bather-load is very small so trying to reduce active chlorine levels further doesn't make a whole lot of sense, especially if you don't have other methods of removing the organic precursors from the water. If you don't remove the dead skin cells and urea from sweat and urine, they will build up in the water at the lower active chlorine level such that their product of concentrations remains roughly the same so the amount of end by-products will be roughly similar. The main exception to this is with nitrogen trichloride in the chlorine oxidation of ammonia (and to some extent possibly with urea), but that level is already extraordinarily low.
The main concern with disinfection by-products is with high bather-load pools, especially indoors. This is where supplemental oxidation systems as well as precursor removal systems become useful, but that's a whole other discussion not really relevant to our outdoor residential pools that are very safe. However, since you seem to be the type that searches the Internet and finds information from all kinds of questionable sources, let me point you to a few responses we've already written to articles and papers regarding disinfection by-products to try and preempt such questions. Read the following posts or threads:
Asthma and Chlorinated Pools -- the Bernard papers
New Chlorine scare -- the triplet of Barcelona papers; read the later posts as well
Alternative to chlorine, peroxide? -- discussion of alternatives
continuation of the above -- includes epidemiological studies
BBB and chlorine health -- some additional and repeated info
Natural Swimming Pools -- one "alternative"
Campbell Environmental Systems -- one of many "alternative" examples that blatantly lie
EcoSmarte -- another example of an "alternative" that blatantly lies
converting my ecosmarte system to chlorine -- a table of relative kill times for chlorine (with CYA) vs. copper and silver ions
Interesting Study (Dissertation) on DBP's in indoor pools -- an analysis of an indoor pool study
Chloramines and FC/CYA -- my calculations using chlorine oxidation of ammonia models
By the way, in case it wasn't clear, I do not have a Ph.D. and though I majored in Physics and Chemistry (a field major -- they didn't allow a double-major since there are too many common math and other courses between these two), I later got an MBA and most of my work has been in computer software programming and management. I am not a chemist. So if you use titles or position alone as a measure of credibility, then you should discount everything that I write. That's one reason I try and refer to credible sources and have you, the reader, use your own abilities to ascertain the truth.