Re-post Of Intro Questions

[SantaMonica]

I would later like to contribute to the knowledge of pool/spa filtration; but first I need to make sure I understand how it currently works:

Is there a large movement to go "green" and use no chemicals at all?

What sanitizer would be considered the most "green" and "non-chemical"?

Do pathogens use ammonia, nitrate and phosphate?

Will keeping phosphate less than .125 ppm prevent bacteria, even if FC is zero?

Do bacteria eat CYA, and convert it to ammonia?

What is the main thing that prevents metals from depositing on surfaces?

Does algaecide dissipate (degrade) on it own?

Since "the overall net reaction of adding sodium hypochlorite to your pool and having it used up in its most typical ways is simply to produce salt", does salinity slowly increase over time with this?

What things build-up in pools, and especially in spa's, so as to eventually require pumping out water, and replacing with new water?

How much chlorine ppm is needed in pools/spas for just sanitation, vs oxidation? 1 ppm FC with 50 ppm CYA?

What happens to the carbon, after waste has been oxidized?

Thanks in advance if anyone can help here!

[chem geek]

Answering your questions inline below, putting your questions in bold for easier distinction.

Is there a large movement to go "green" and use no chemicals at all?

There are only a very small number of people going "green" as you described it with "natural" pools adding virtually no chemicals. These fall basically into two camps. Those using sphagnum moss or other natural filtration and bacteria inhibition systems and those using metal ions, usually copper or silver. The latter is obviously not as natural as the former, but it does inhibit algae growth. For spas, there are some additional systems using enzymes, but most of these systems still use at least an oxidizer of some sort in order to oxidize bather waste. Otherwise, you will end up soaking in your own sweat and urine.

It should be noted that none of the above are EPA-approved sanitizers and none will kill pathogens as quickly as EPA-approved sanitizers (i.e. those products that can be called disinfectants that pass EPA DIS/TS-12). There are only four EPA-approved sanitizers for spas (three for pools): chlorine, bromine, Baquacil/biguanide/PHMB, Nature2 with non-chlorine shock (potassium monopersulfate aka MPS). The first three are also approved for pools (the latter is not because hot temperature is required for the silver ion plus MPS combination to be fast enough killing pathogens).

What sanitizer would be considered the most "green" and "non-chemical"?

Of the EPA-approved sanitizers, none, though N2 with MPS might be considered closer since it does not use halogens. On the other hand, copper is toxic to plant life which is what has it kill algae, but that makes it not "green" in terms of dumping the water into waterways and water treatment systems do not easily remove such metal ions. At least with chlorine, it is easily neutralized. The main problem with chlorine and bromine are the disinfection by-products, though the Dichlor-then-bleach method is designed to minimize those while still providing sufficient sanitation. Baquacil/biguanide/PHMB is sort of in-between since it doesn't have the disinfection by-products, but isn't as readily eliminated in water (though it can be oxidized -- it just takes a lot of oxidzer to do so).

Do pathogens use ammonia, nitrate and phosphate?

Yes, most pathogens (bacteria, protozoa) and algae (which is unsightly, but not really a pathogen) require a source of carbon (usually carbonate or carbon dioxide), a source of nitrogen (usually nitrate or ammonia or sometimes nitrogen gas for nitrogen-fixing bacteria), a source of phosphorous (usually orthophosphate, though some organic phosphates can also be utilized more slowly) and of course oxygen. Algae and other photosynthetic species require sunlight as well. All require water. Viruses don't grow outside a host so don't require anything (i.e. they just hang out until they enter a host where they can then reproduce).

Will keeping phosphate less than .125 ppm prevent bacteria, even if FC is zero?

No, not really. It will help slow down the growth of algae and may slow down the growth of bacteria, but it won't stop it from growing. Phosphate removal products (most of which are lanthanum chloride) only remove orthophosphate and do not remove organic phosphates that can still be used for growth, albeit more slowly). The most effective way to prevent pathogen growth and even algae growth is with chlorine since very low levels of active chlorine can keep bacteria from growing and inactivate viruses. Somewhat higher levels (around 0.07 ppm FC equivalent of chlorine with no CYA) can prevent algae from growing in spite of high nutrient (phosphate, nitrate) levels. For example, my 16,000 gallon pool shown here and here has had 2000-3000 ppb phosphates (my fill water has 300-500 ppb phosphates) yet remains algae free through maintaining an appropriate FC/CYA ratio with chlorine alone. No phosphate removers, no algaecides, no clarifiers (and I've got a cartridge filter, not DE), nothing but chlorine until this year when I added borates mostly as insurance so if the chlorine did get to zero for any reason I wouldn't have quite as rapid bacteria or algae growth.

Do bacteria eat CYA, and convert it to ammonia?

They can, but it's not guaranteed. The process is described in this post. If you have a sanitizer in your pool, then the bacteria are killed before they can grow and consume CYA. That is, you would need the FC to get to zero to have bacteria convert CYA into ammonia, but you can't coax them to do so and usually they don't (though they did in my own pool when I let the chlorine get to zero accidentally one time).

What is the main thing that prevents metals from depositing on surfaces?

Keeping the pH and TA lower. Metals themselves don't stain. It's certain metal compounds with oxygen or hydroxide or carbonate that stain. If the metal concentration is higher or the pH or TA are higher (or very high CYA), then it is more likely for the metal compounds to form and then stain. Metal sequestrants bind to metal ions preventing them from combining with other compounds but that also prevents them from actively killing pathogens so it's really just a buffer for metals. You can only ultimately remove the metals through dilution with water free of metals.

Does algaecide dissipate (degrade) on it own?

Most do (in pools and spas), but not all. The linear quat and PolyQuat algaecides will break down (get oxidized) over time which is why you generally add them weekly. Copper ions won't break down nor will borates (boric acid).

Since "the overall net reaction of adding sodium hypochlorite to your pool and having it used up in its most typical ways is simply to produce salt", does salinity slowly increase over time with this?

Yes it does unless you dilute the water with fill water that is less saline (as is usually the case).

What things build-up in pools, and especially in spa's, so as to eventually require pumping out water, and replacing with new water?

It depends on the sanitizer system you are using. With N2 and MPS, the buildup is mostly sulfates from the MPS. With Dichlor-then-bleach, the buildup is mostly chloride. With bromine, you build up bromide. With all systems, there is a buildup of partially oxidized organics since none of the systems fully oxidize everything (though ozone does a decent job). However, most of sweat and urine is urea and ammonia and these are mostly fully oxidized to nitrogen gas and carbon dioxide (and some nitrates). Creatinine may get fully oxidized as well, but may produce some other disinfection by-products. Lotions and other organics may not get fully oxidized though may get filtered.

With Trichlor and Dichlor, you will build up Cyanuric Acid (CYA), while with Cal-Hypo you will build up Calcium Hardness (CH). With bromine tabs, you will build up 5,5-dimethylhydantoin (DMH).

How much chlorine ppm is needed in pools/spas for just sanitation, vs oxidation? 1 ppm FC with 50 ppm CYA?

It depends on what level of sanitation you want. Most bacteria are incredibly easy to kill so preventing their runaway growth can be done with as little as 1 ppm FC with 200 ppm CYA or even lower levels. However, such levels won't kill the bacteria fast enough to prevent person-to-person transmission (usually via the fecal to oral route). To kill most bacteria within 1-2 minutes for a 99% kill, you would need the FC to be roughly around 10% of the CYA level though 20% would be a bit safer for commercial/public pools. To prevent algae growth, in a manually dosed pool the minimum FC is around 7.5% of the CYA level (in an SWG pool, it's an FC of around 4.5% of the CYA level). Also, for spas, the bacteria that causes hot tub itch, Pseudomonas aeruginosa, may be heartier and require closer to the algae prevention levels of chlorine to kill them before they form biofilms.

For oxidation, the amount of oxidizer needed depends on the bather load. For spas, a rough rule of thumb is that each person-hour of soaking in a hot (100-104F) spa requires around 3-1/2 teaspoons of Dichlor or 5 fluid ounces of 6% bleach or 7 teaspoons of non-chlorine shock (43% MPS). If an ozonator is used, then less oxidizer is needed since ozone takes over some of the oxidation. A swimmer in a cooler (80-85F) pool would probably require around half this amount of oxidizer per person-hour. In residential spas, bather load is the primary consumer of oxidizer. In residential pools, the bather load is very low and it is sunlight that uses up the most chlorine.

What happens to the carbon, after waste has been oxidized?

For substances that get fully oxidized, such as urea, the carbon becomes carbon dioxide. For substances that don't get fully oxidized, the carbon remains in the partially oxidized products.

Hope that helps,

Richard

[PaulR]

Since "the overall net reaction of adding sodium hypochlorite to your pool and having it used up in its most typical ways is simply to produce salt", does salinity slowly increase over time with this?

Yes it does unless you dilute the water with fill water that is less saline (as is usually the case).

I think it should be said that this effect is relatively miniscule. Typical salt concentrations in a spa (with water completely replaced every few months) would be undetectable. In chemically maintained pools you'd expect to see some hundreds to as much as low thousands of ppm salt, with a SWG pool you add massive quantities of salt directly to achieve on the order of 3000 ppm. At that level, some people say they can taste it, others say they can't. By contrast, sea water is more like 35,000 ppm.

--paulr

[SantaMonica]

Some great advice, thanks.

Those using sphagnum moss or other natural filtration and bacteria inhibition systems and those using metal ions, usually copper or silver.

The moss technique is news to me. Sounds like it could be made into a natural habitat looking setup. Will search for more info about it. As for the sanitizers, looks like nature has no good options. Interesting that the main concern is the disposal of the water; I would have thought that the main concern would have been potential pool/spa owners who did not want chemicals on their skin and in the air.

The most effective way to prevent pathogen growth and even algae growth is with chlorine since very low levels of active chlorine can keep bacteria from growing and inactivate viruses.

I see how chlorine helps do both, and I personally like chlorine, but I am keeping in the back of my mind a sizable percentage of people who won't go the chlorine route because of their unfounded perceptions.

With all systems, there is a buildup of partially oxidized organics since none of the systems fully oxidize everything

How do these organics display/reveal themselves in the water? How do you know they are there?

Lastly, if someone came along and said, "I'm getting rid of my pool (or spa) unless you can show me how to operate it with far less chemicals", or "I'll install a pool (or spa) if you can show me how to operate it with far less chemicals", what could they be told?

[Nitro]

Lastly, if someone came along and said, "I'm getting rid of my pool (or spa) unless you can show me how to operate it with far less chemicals", or "I'll install a pool (or spa) if you can show me how to operate it with far less chemicals", what could they be told?

IMHO, the Dichlor/Bleach method (see below), if done correctly, uses the least amount of chemicals, is the cheapest and safest method there is. Anyone not willing to use Chlorine (or Bromine), has a much higher chance of having problems. Especially with high bather loads.

[chem geek]

I think it should be said that this effect is relatively miniscule. Typical salt concentrations in a spa (with water completely replaced every few months) would be undetectable. In chemically maintained pools you'd expect to see some hundreds to as much as low thousands of ppm salt, with a SWG pool you add massive quantities of salt directly to achieve on the order of 3000 ppm. At that level, some people say they can taste it, others say they can't. By contrast, sea water is more like 35,000 ppm.

--paulr

The rate of salt buildup depends on the amount of sanitizer used, but let's take a typical scenario of a daily 30-40 minute soak requiring roughly 4 ppm FC per day in 350 gallons to oxidize the bather waste and maintain a chlorine residual. After the first week of Dichlor, the bleach would increase the salt level by around 200 ppm per month so even after 6 months you're only looking at a salt increase of around 1200 ppm. As Paul points out above, that's far less than found in saltwater chlorine generator (SWG) pools and is also less than you would be able to taste. It is also, fortunately, fairly low with regard to any corrosion issues, but it is one reason why changing the water after 6 months for this example might make some sense. That's still probably twice as long as one would get with their spa water if they used Dichlor-only and the water clarity would be much better with Dichlor-then-bleach even after 6 months.

[chem geek]

The moss technique is news to me. Sounds like it could be made into a natural habitat looking setup. Will search for more info about it. As for the sanitizers, looks like nature has no good options. Interesting that the main concern is the disposal of the water; I would have thought that the main concern would have been potential pool/spa owners who did not want chemicals on their skin and in the air.

:

I see how chlorine helps do both, and I personally like chlorine, but I am keeping in the back of my mind a sizable percentage of people who won't go the chlorine route because of their unfounded perceptions.

:

How do these organics display/reveal themselves in the water? How do you know they are there?

:

Lastly, if someone came along and said, "I'm getting rid of my pool (or spa) unless you can show me how to operate it with far less chemicals", or "I'll install a pool (or spa) if you can show me how to operate it with far less chemicals", what could they be told?

Just search for "natural pools" and you'll see a bunch of different alternatives. Nature isn't bad as most natural waters aren't terribly harmful, but they generally do have pathogens in them -- it's just that healthy people usually fight off whatever is there. Sometimes, some particularly nasty pathogen emerges and people can get sick (or even die in very rare cases as described here). More commonly, however, is that the fecal matter from people transmits diseases from person-to-person as described here. Since most commercial/public pools are now properly sanitized (usually with chlorine), the most common outbreaks are with the Cryptosporidium protozoan oocysts since they are very resistant to chlorine.

Some have argued that with residential pools and spas the risks are lower since you aren't having many people use these facilities, and that is probably true, but the risk for a "natural" pool or spa is still higher than a properly sanitized pool or spa. There are no laws governing what you do with your own personal pool or spa in terms of sanitation so it's really up to you. For spas, however, going natural is more troublesome since the bacteria that causes hot tub itch, Pseudomonas aeruginosa is far more common and can cause problems for some people.

As for the main concern with pool/spa owners, you are right that they don't think much about the disposal issues and are more focused on the effects of the chemicals on their bodies while in the water. I was just trying to give you a broader spectrum of issues to think about.

For those that don't want chlorine or bromine, I think you should offer Nature2 with MPS (for spas). After that, the choices start to have more risks or issues.

As for unoxidized organics, the most common symptoms would be cloudiness, foaming, water-line films, "sluggish" water and a higher-than-normal oxidizer demand. Such symptoms are more prevalent when organics are oxidized too slowly as often happens when using Dichlor-only after a month or two (due to the buildup of CYA). When the oxidation is more complete, these symptoms either don't show up or take a lot longer (i.e. require more buildup) before they become noticeable.

I agree with Nitro that Dichlor-then-bleach is pretty minimal and certainly very low cost with chemicals (for those who simply don't want to use bleach, they can use lithium hypochlorite powder, but it's over 5 times the cost). Once you get your water balanced after a fresh refill, everything is pretty stable with the only extra chemical needed being occasional acid if the pH rises. Unless you have an ozonator, you pretty much have to add an oxidizer of some sort in sufficient quantity to get rid of bather waste (even with an ozonator you have to do this, but can use less oxidizer). Since you add the chlorine after the soak and since the chlorine level is usually around 1 ppm FC when you start the soak (and there is 30 ppm CYA), the exposure to chlorine and by-products is minimal with most people not even noticing a smell. Technically, there is higher risk while soaking with no chlorine but if it's just your own family then the risk is pretty small and the chlorine after the soak will kill off whatever is shed during the soak (bacteria take 15-60 minutes to double in population so they don't grow very much even during an hour of soaking). If you're throwing a hot tub party, you can always ramp up the chlorine or other sanitizer/oxidizer before the soak.

For pools, it's similar except that you usually increase the Cyanuric Acid (CYA) level by adding pure CYA initially. After that, it's just bleach or chlorinating liquid. I only use 12.5% chlorinating liquid twice a week in my own pool (remember I have a mostly opaque pool cover) plus a small amount of acid every 1-2 months. It only costs me $17 per month in these chemicals for a 16,000 gallon pool. My pump electricity costs, on the other hand, are much, much higher, mostly due to the solar heating with its required flow rates. For pools, you can see how there are over 20,000 members at The PoolForum and over 10,000 members at Trouble Free Pool most of whom have taken charge of their own pools by using a good test kit (the Taylor K-2006 or equivalent) and mostly using chlorine alone with a proper FC/CYA ratio to maintain their pools. If you don't want to add chlorine every day or two, then you can get a peristaltic pump or The Liquidator or a saltwater chlorine generator (SWG).

Richard

[quantumchromodynamics]

Is there a large movement to go "green" and use no chemicals at all?

I think that a lot of the "green" movement is well intentioned, but misguided. Much is based on feel-good nonsense rather than hard science. Even so-called "Science" or "Education" shows routinely get their facts wrong.

Many manufacturers end up doing stupid things that are actually more harmful to the environment, but these things sell because the PR sounds good.

The level of science education in this country is abysmal. A good example is shown here:

[SantaMonica]

As for unoxidized organics, the most common symptoms would be cloudiness, foaming, water-line films, "sluggish" water and a higher-than-normal oxidizer demand. Such symptoms are more prevalent when organics are oxidized too slowly as often happens when using Dichlor-only after a month or two (due to the buildup of CYA). When the oxidation is more complete, these symptoms either don't show up or take a lot longer (i.e. require more buildup) before they become noticeable.

Is this correct that this cloudiness is algae in the water column, and the water-line films are bacteria? In other words, these two things are not made of organics; just cause by organics.

[chem geek]

Continued use of stabilized chlorine products in a pool will build up CYA (unless there is very significant water dilution) and that can lead to algae growing faster than chlorine can kill it if there are sufficient algae nutrients. This initially shows up as higher chlorine demand, but then the water turns dull, then cloudy, and eventually green.

However, in a spa, it is far less likely (though not impossible) for there to be algae growth, especially if the water is kept hot and the cover is on and dark most of the time. As for bacterial growth, if there is at least some chlorine, even at higher CYA, then most bacteria will be killed though hot tub itch bacteria could form some biofilms at some point. Not all spas "turn" that quickly on Dichlor-only so I suspect it depends on the lotions and soaps and skin oils introduced into the spa. Some of these don't oxidize as readily so if the CYA builds up to slow down chlorine oxidation, then that buildup could cause the problems I described. Also, these situations are usually when there is no ozonator. When one has an ozonator, then one gets extra oxidation. Generally, this is good, but it does tend to increase the chlorine demand when not using the tub (the ozone may oxidize chlorine to chlorate and may accelerate its outgassing).

Every situation is a bit different so if in some spas the sanitizer gets towards zero, then bacteria could grow and biofilms could form. Certainly, if spa surfaces start to feel slimy at all, then that is likely to be what is happening so in that case it isn't organic chemicals but living bacteria that would be a problem.

[SantaMonica]

Do you happen to know what mechanism moss uses for filtration?

[chem geek]

They are just treated like regular filter materials and put in the regular circulation/filtration path, though they probably have their own filter containers. There is a member here, aschwartz (Allan Schwartz), whose company sells a sphagnum moss filter product (SpaNaturally) so hopefully you'll get a post from him. Note that you still need to use an oxidizer and that there is no sanitizer in the bulk water itself (i.e. nothing to prevent person-to-person transmission of pathogens via the fecal-to-oral route, for example) and the claim is that biofilms on pool surfaces away from the filter won't form due to substances put into the water by the moss that disrupt such biofilm formation.

[SantaMonica]

I guess my question was, chemically, how the moss works. After all, it is dead moss, right? Maybe the "substance" put into the water is it. I read that the moss is not compatible with baqua, and maybe that is why.

[chem geek]

Well "works" is a relative term. Moss alone is not allowed in commercial/public pools since it is not a sanitizer or disinfectant by itself so chlorine is typically still used. The moss does two things. One is that it acts as a filtration medium and some argue that it is superior to sand because it will not form biofilms. It is true that some sand filters will have poor circulation in some areas and develop biofilms and then have serious channeling rendering them not only ineffective, but sources of bio-activity that can use more chlorine (oxidizing biofilm surfaces) and possibly generate more nitrogen trichloride. The other effect moss is claimed to have is to release certain chemicals that inhibit biofilm formation, presumably even in the bulk pool water.

You bring up an interesting point about dead moss. One argument that is used in promoting moss products is comparing them to the relatively clean water found in some bogs where the moss is found. However, to the extent that these properties of moss are from the moss being alive, this would not happen in a properly sanitized pool because the chlorine would tend to kill the moss (which is a plant, after all). So it's unclear to me whether the moss used in filters is really doing anything similar to live moss or whether it is simply a better surface material for filtration that inhibits biofilm so is better than "poor" sand filters. If this is the case, then other filters, such as Dryden Aqua Active Filter Media® (AFM) may work just as well since the material is designed to inhibit biofilm formation in the filter.

Richard

[SantaMonica]

And how about this: Being dead organic matter, wouldn't the moss slowly decay like leaves or anything else, and add nutrients to the water?

[chem geek]

And how about this: Being dead organic matter, wouldn't the moss slowly decay like leaves or anything else, and add nutrients to the water?

In theory, yes, but the makers of these products claim a reduction in chlorine demand, not an increase, but this is relative to the previous sand filters. I suspect that the moss is either treated or has a natural slow resistance to chlorine oxidation, but that's just speculation on my part. Microscopic organisms and related material including bacteria, protozoa, viruses, algae and pollen all exhibit far greater chlorine demand, mostly due to the high surface area to volume ratios and the presence of lots of nitrogenous compounds that react with chlorine. Leaves and other larger materials also have a chlorine demand, but much smaller relative to their volume at least partly due to the much smaller surface area to volume ratio and the fact that chlorine reacts rather slowly with cellulose at normal pool pH (faster reaction rates occur at much more acidic pH). Cellulose is a polysaccharide that is not nitrogenous (it's a long chain of glucose units). This is a good part of the reason why it takes far more chlorine to kill most algae (that has cellulose) than it does to kill most bacteria (which does not have cellulose) as disruption of the cell wall is one of several mechanisms for bacterial kill. The surface area to volume effect is multiplied for something as large as a leaf where the surface cells may be killed (if not already dead), but the chlorine doesn't penetrate very deeply very quickly. As you've probably noticed in pools, it takes a while for leaves to start to degrade.

Anyway, the surface area of the moss for good filtration must be pretty high so the material must be fairly resistant to chlorine degradation or else there would be increased chlorine demand. You're asking great questions, but really they should be directed to the makers of the sphagnum moss filters and I wish that Allan would respond to them.

[SantaMonica]

Does any person or site know how many private pools and spas are in the U.S. and the world?

Anyone not willing to use Chlorine (or Bromine), has a much higher chance of having problems. Especially with high bather loads.

I think this is the crux of a pool/spa marketing problem. However many pools and spas there currently are, there are probably two or three times that many people who would like to have a pool or spa (and who have the money and the space), but can't tolerate even the thought of the chemicals. And with the green movement in general, this has not gotten any better.

I think that a lot of the "green" movement is well intentioned, but misguided. Much is based on feel-good nonsense rather than hard science.

Consumers, of course, make buying decicions based on perception.

Dichlor-then-bleach is pretty minimal and certainly very low cost with chemicals (for those who simply don't want to use bleach, they can use lithium hypochlorite powder, but it's over 5 times the cost).

Does this still get disinfection byproducts?

[chem geek]

According to this report of market research in 2007, there are 8.6 million swimming pools in the U.S., but this is not broken down by private vs. commercial. Nevertheless, I'm sure that the vast majority of pools are private. Most of these are probably the less expensive above-ground pools that are probably smaller (7500 gallons) while the rest are in-ground pools that are larger (15,000-25,000 gallons), though that's just a guess on my part. I didn't search for a link on the number of spas.

When you say that there are lots of people with money and desire for a pool or spa but don't want the chemicals, I would say that it's more that they don't want the perceived inconvenience of having to maintain the pool either through paying a pool service or having to maintain it themselves. This is why the majority of new in-ground residential pools today are saltwater chlorine generator (SWG) pools -- mostly for the convenience, not for avoiding chlorine (because it doesn't avoid chlorine). Yes, I'm sure there are people who want chemical-free pools, whatever that means (more accurately would be to say halogen-free), but those are already available today especially if you are willing to take the higher risk. There are no laws saying how private pools must be sanitized -- you can do whatever you want -- it's only commercial and public pools that are regulated (generally at the state or county level).

As for Dichlor-then-bleach in spas, yes there are still disinfection by-products (DBPs), though the amount of nitrogen trichloride is low and controlled. In practice, most people using this method and indeed the Dichlor-only method tend to start their soak with no more than 1 ppm FC and then add chlorine after their soak. By doing this, they are exposed to a minimum of DBPs during the soak and also avoid smelling chlorine and most are produced after the soak and the volatile ones dissipated before the next soak (especially if the cover is left open for a short time after the soak and before the next soak). But of course, as you point out, some consumers buy on perception, not facts. If someone wants a close to halogen-free spa, then the Nature2 plus MPS would be the way to achieve that while still getting disinfection (according to Nature2 and EPA; Vermonter found this not to be true in the past). It might still need every week or two shocking with chlorine, but you don't have to be in the spa during that shock period and therefore not exposed to the bulk of the DBPs which will be lower anyway due to the regular MPS (i.e. the chlorine will only be oxidizing chemicals that MPS doesn't).

By the way, PStores in this thread is finding no problems with SpaNaturally which uses sphagnum moss strips, but then many people doing nothing for sanitation don't have problems -- it just increases the risk and is also dependent on the sensitivity of the person to bacteria (say, from cuts, abrasions, sensitive skin). Nevertheless, a lack of EPA-approved sanitizer kept at non-zero levels was the primary reason for hot tub itch/rash/lung as listed in this post where I used to compile the reports from mostly this forum.

[SantaMonica]

The DBP's.... are they really from sanitizing, or from oxidizing?

[chem geek]

The DBP's.... are they really from sanitizing, or from oxidizing?

They are from neither, technically, at least what most people refer to as DBPs which are the harmful ones. They are from the halogen (chlorine or bromine) combining with an organic (or with ammonia) to form a new compound. The chlorine usually substitutes with a hydrogen that is attached to a nitrogen; it is a substitution reaction, not a redox (reduction/oxidation) reaction. Think of the simplest case where ammonia (NH₃) combines with chlorine to form monochloramine (NH₂Cl) and with more chlorine to form dichloramine (NHCl₂) and even more chlorine to form nitrogen trichloride (NCl₃) with the latter being the most irritating and most volatile, but is also the easiest to control by keeping the active chlorine concentration low. You can see how an additional hydrogen attached to nitrogen gets substituted with a chlorine through this progression.

Oxidation can also produce new chemical products, but these usually aren't harmful. Not all combinations of chlorine or bromine with organics are harmful either, but some are if in large enough quantities. Oxidation using a non-chlorine shock such as potassium monopersulfate (MPS) will obviously not produce any chlorinated or brominated organic or inorganic byproducts. It will produce new oxidized chemical products, but as far as anyone knows, these aren't any worse than the original chemicals (i.e. urea, ammonia, creatinine, etc.). For simpler chemicals, complete oxidation occurs. This is true for both ammonia and urea, for example. Nevertheless, most N2+MPS users report getting dull or cloudy water if they don't also shock with chlorine once in a while while most Dichlor-then-bleach users don't generally need to use MPS (though some do). Though both chlorine and MPS will oxidize compounds such as urea and ammonia, they are each selective oxidizers (in terms of reaction rates) so each will effectively oxidize some compounds the other will not.

[SantaMonica]

I found this:

"The moss readily absorbs heavy metals, including iron, which often encourages microbial growth. Without any iron in the water, microbes can't grow." here:

http://news.discovery.com/earth/swimming-p...moss-green.html

Would this be accurate?

[chem geek]

Sphagnum moss has cationic exchange capability so would absorb iron similar to a water softener. However, iron is a micronutrient for bacteria and algae, not a macronutrient like phosphorous so though the moss could take the edge off of rapid growth (though keep reading below since I have my doubts), it wouldn't stop growth. It wouldn't, for example, kill bacteria quickly enough to prevent person-to-person transmission and therefore would not replace a fast-acting sanitizer such as chlorine in commercial/public pools. In that sense, one could think of it similar to having metal ions of silver or copper in the water that also take the edge off of growth, but are not enough by themselves to kill newly introduced pathogens quickly enough. Or it is somewhat similar to what phosphate removers do in terms of reducing algae growth rates (though they don't remove organic phosphates and only lower phosphates to 50-100 ppb).

This link interestingly talks about removing iron from mine waste water using wetland water treatment systems, but you will note that such systems support sulfate-reducing bacteria so even though higher iron levels are lowered significantly, they do not appear to be lowered to a level that kills the bacteria. It is relatively easy for a cationic exchange system to remove higher levels of cations such as iron from mine waste, but as they get to rather low levels it becomes increasingly more difficult and as a micronutrient, the amount of iron needed by bacteria is very, very low.

What disturbs me is that those selling sphagnum moss systems make quotes such as you describe, but they don't give specific iron reduction levels to what these systems actually achieve and then compare that to bacterial growth rates at those iron levels. This is similar to claims by phosphate remover manufacturers that say "no phosphates, no algae" -- both of which are not true since the removers don't remove all phosphate types or amount. It is also similar to the claims from zeolite filter manufacturers that no ammonia, no chloramines, no eye irritation as this is also not true in that in a properly chlorinated pool there is essentially no ammonia since it rapidly gets converted to monochloramine (and eventually gets oxidized to nitrogen gas) and the zeolite filters do not remove monochloramine (though they do remove ammonia). So circuitous arguments and claims are easy to make, but at the end of the day they are simply misleading.

[SantaMonica]

So on other natural pool methods, like this one...

http://www.naturalswimmingpools.com/pdfs/r...otop%20pool.pdf

... they are not doing anything about sanitizing, correct?

[chem geek]

So on other natural pool methods, like this one...

http://www.naturalswimmingpools.com/pdfs/r...otop%20pool.pdf

... they are not doing anything about sanitizing, correct?

This system is just putting a phosphate remover in the filter rather than separately adding it. It will take the edge off of algae growth, but won't completely remove orthophosphates and does nothing about organic phosphates. This also won't stop bacterial growth. There is no sanitizer in this system and it is not clear how they are oxidizing bather waste such as the urea and ammonia from sweat and urine. I suppose you just end up swimming in it if you truly don't add any chemicals at all (i.e. no oxidizers, let alone sanitizers).

Again, there is no law or regulation saying what a residential pool owner can use for their pool. You can do whatever you want. However, such a system without a bulk sanitizer would not be allowed in a commercial/public pool in any state since they all require some form of fast-acting sanitizer in the bulk pool water to kill most pathogens quickly enough to prevent person-to-person transmission of disease, not just uncontrolled growth.

It's not that these systems (sphagnum moss, phosphate removers) don't do anything, but rather that they do not completely eliminate the need for a fast acting sanitizer in the bulk pool water -- that is, unless you want to just take the increased risk which is, of course, smaller in a residential pool since you usually aren't swimming with a bunch of strangers and the number of people who can get sick is relatively limited. Basically, think of swimming in bath water that you never change and you'll be closer to any of these systems that don't use some kind of oxidizer to get rid of bather waste.

[quantumchromodynamics]

The "Daldrup" pool that they show in the pictures looks pretty nasty. It looks like it has lots of mustard algae.