Bartier Disinfection Index

[chem geek]

Also, my understanding of MPS is that it will not break down chloramines....

I can understand the benifits of MPS with an indoor pool but the caveat seems to be that a residual of MPS is required in the water at all times for them to be effective in the prevention of the formation of chloramines. I see no real advantage to their use in outdoor pools.

Yikes! I had no idea that MPS didn't oxidize monochloramine, but the Dupont literature certainly implies that MPS only prevents their formation. Ben told me that supercholorination to achieve breakpoint almost never works, especially for indoor pools with poor air circulation. He speculated that sunlight breaks down monochloramines in outdoor pools and I've read literature that suggests the same thing.

So this begs the question of how do you get rid of monochloramines? If a pool has CYA in it, then you need a heck of a lot of chlorine to properly shock it. Originally I was thinking that a small amount of CYA for indoor pools was a good idea to reduce effective chlorine concentrations to minimize exposure to bathers (and their swimsuits), but that would make superchlorination even more difficult. A real catch-22. Why wouldn't you use a constant level of MPS to prevent monochloramine formation? Is this not necessary in outdoor pools due to the breakdown from sunlight?

(NOTE: I have contacted Dupont to ask them if their MSP product, Oxone, will oxidize monochloramine in which case it could be used as a shock and not just as a chloramine preventative. I will let you know their response, if any.)

[chem geek]

Okay, I got a response from DuPont on Oxone, but I'm not sure how to be diplomatic about this since I don't want to burn any bridges. I suppose I will paraphrase the jist of the response.

The response I got was essentially that combined chlorines are always being formed as people go into the pool, swim, and prespire. There is no technology on the market today that gets rid of persistent combined chlorines [I suppose that's by definition of "persistent"]. Using chlorine as a shock will oxidize some contaminants, but it will also lead to an increase in combined chlorine [again, I suppose he's talking about the "persistent" variety of combined chlorines since the shocking would probably dispose of the "easier" combined chlorines]. Since Oxone [MPS] is non-chlorine, it cannot form chloramines [very true]. Also, by eliminating periodic high chlorine doses, one reduces chloramine formation [here it sounds like he's talking again about the more complex organic chloramines, not the simple ammonia-based monochloramine]. In pool water samples, they have seen destruction of the "monochloramine" component of combined chlorine by Oxone. This "monochloramine" component is almost certainly not NH2Cl, but a chloramine species which mimics NH2Cl in the DPD test [again it sounds like this is an organic chloramine]. In fact, NH2Cl cannot exist in actual pool water where there is always a free chlorine residual [I believe he is talking about the breakpoint reaction of chlorine preventing NH2Cl from remaining].

I then wrote back with more details and questions (such as the breakdown of monochloramines by sunlight, the impact of CYA on low HOCl and low breakpoint rates, the differences of outdoor and indoor pools, etc.), but haven't heard back and may not. So what's the bottom line? Using MPS in a preventative dosage will likely prevent chloramines of any type from forming so shocking with chlorine will not be necessary and may not work completely anyway (at least for that purpose -- it would still be needed for killing algae blooms but they shouldn't happen at all if chlorine levels are maintained).

Since I have not seen any significant reports from users of this forum on battling Combined Chlorine when using BBB or other methods that do not use non-chlorine shock, it would appear that the use of MPS may not be necessary in residential outdoor pools (commercial pools with high bather loads might be different). On the other hand, there are frequent reports of problems with indoor pools so perhaps MPS would be quite useful in maintenance doses in that environment. What we don't know for sure is what exactly is the difference between these two environments that is the root cause of the CC difference that makes outdoor pools much easier to manage. Is it the sunlight (UV) breakdown of choramines? Is it the greater air circulation? Is it the use of CYA (doubtful)?

[EDIT] For an alternative point of view based on experience, read Ben's tip. I'm giving the DuPont Oxone a little more credit for possible benefit in indoor pools. I am also one with the heretical idea of using a small amount of CYA (10 ppm or less) in indoor pools to lower the effective chlorine concentration to reduce exposure to clothing and people. However, using CYA means that superchlorinating is much harder, but if the CYA amount is small enough, then you can fairly easily overwhelm the CYA and get lots of pure chlorine in your pool during shocking (e.g. 15-20 ppm chlorine), but that's a topic for another thread (someday)! [END-EDIT]

Richard