I've been answering PMs from
tripledobe (Koni) on this subject, but wanted to clarify a few things in this thread so that the incorrect information doesn't get propagated.
tripledobe said:
I am not concerned with transferring infection between the members of my family or anyone urinating in the pool.
Given that even fecal matter is found on many cell phones (see
this article, among many), I can see where you wouldn't be concerned with ingesting your own or your own family's fecal bacteria and given the close contact among family members you are probably sharing many viruses anyway. On the other hand, at least in my family, my wife treats me as if I have leprosy when I have a cold and has me wash my hands as if I'm Lady Macbeth. The thing about warm water in a pool or spa that has organic material is that bacteria can use the nutrients to reproduce and grow hugely in number. They can then overwhelm your immune system when ingested and cause illness.
So at a minimum you would want to prevent uncontrolled bacterial growth. The use of metal ions is often touted for that purpose, but if you look at the actual kill times such as those I compiled in
this post, you will see that neither silver nor copper alone are sufficient to prevent uncontrolled bacterial growth. A combination of silver and copper is OK to prevent runaway growth of most bacteria, but does not handle most viruses nor protozoan cysts. Of course, silver/copper do not kill quickly enough to prevent person-to-person transmission, but that doesn't sound like a concern of yours. And, of course, metal ions can stain pool surfaces, especially plaster. Even a small amount of chlorine equivalent to 0.1 ppm FC with no CYA kills or inactivates most pathogens orders-of-magnitude more quickly than metal ions. Ozone isn't even a factor since it does not persist in the bulk pool water and most bacteria growth is on pool surfaces, not free-floating through the ozonator.
tripledobe said:
How much is the minimum FC that I need and why? I have read alot from the Pool School and nowhere did I find any explanation about why I need chlorine if I would be the only one using a pool that I have and not concerned with algy. It's indoor, the slow rate of disinfection should not matter if there is only one person using it, correct? I am using silver and Ozone, shouldn't it be enough? I know the answer is NO under most circomstances but I would like to know why I need it in this particular situation if it is not too much trouble to ask.
As noted above, one needs something in the bulk pool water to kill bacteria and inactivate viruses and, to some degree (though less of a risk), protozoan cysts. It's a spectrum of risk with copper/silver lowering the risk but not nearly as much as chlorine. As far as the minimum FC/CYA ratio (FC level alone is meaningless unless you don't have any CYA in the water), this depends on the level of disinfection and oxidation that you are looking for. If you have an ozonator that is not as woefully inadequate as most residential pool ozonators are, then if you've got something to prevent algae from growing (copper ions or algaecides) then having the FC/CYA ratio be lower is certainly an option. However, even with an FC/CYA in the more normal range near 10%, the active chlorine level is equivalent to 0.1 ppm FC with no CYA so is very low -- far lower than any commercial/public pool in the world that isn't using any CYA. And, of course, if you are using chlorine, then you don't have any need for metal ions.
tripledobe said:
I would like to get a better explanation on where the bodily waste comes from if a person (let's assume only one using pool) takes a good shower every time before swimming. This situation might sound unrealistic but I think it would give me a clearer picture in case I am missing something.
:
There are multiple articles pointing to research on the harm that chlorine might cause which I read after ChemGeek mentioned links to them (mainly European research) in addition to some others that I have found. That harm might be less dangerous than absence of chlorine under some circumstances and might be more under others. The devil is always in the details when one tries to solve an optimization problem.
Even if one showers and washes thoroughly before swimming, one still releases small amounts of fecal bacteria and around 100 ml of sweat (per hour) and 25-50 ml of urine. In warm water, the muscles relax and you don't even notice most releases. Read
this link for many examples of waterborne illnesses in recreational water and how in treated water venues the lack of proper disinfection is the primary cause (the only exception being the protozoan oocyst
Cryptosproidium parvum since that is very chlorine-resistant).
As for Europe, their commercial/public pools in most countries use chlorine as that is required by the DIN 19643 standard (
19643-1,
19643-2,
19643-3,
19643-4,
19643-5). This standard requires 0.2-0.5 ppm FC (with no CYA) chlorine to be used when an ozonator is used and 0.3-0.6 ppm FC when an ozonator is not used.
As for balance, if you use chlorine with CYA in the water, then you will have a lower active chlorine level than the DIN 19643 standard. However, the expensive additional equipment such as microfiltration, activated carbon, flocculation, etc. is designed to minimize disinfection by-products (DBPs), but is there primarily due to the higher bather loads in commercial/public pools. If your ozonator is halfway decent, then it should oxidize much of the bather waste to reduce these DBPs though the slow turnover time will still have chlorine react with some of your bather waste and will react with your skin, though at a slower rate than in the European pools because of your lower active chlorine level.
