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Bleach In Hot Tubs


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#1 chem geek

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Posted 12 January 2008 - 12:09 PM

I received the following question in a PM but am posting it here anonymously so it doesn't have to get asked and answered many times.

QUOTE
Hi,
I have been trained in water chemistry for hot tubs and have taken several classes. First, I hace always been taught never to use bleach in a hot tub. Only di-chlor. They are 2 different types of chlorine, different PH and di-chlor hols up the best in hot water. Alot of tub manufactures will void the warranty if they find you are using bleach (or Baqa Spa for that matter!) I have also been taught that if you cant use dichlor since it has to been put in manually on a daily basis, to use the small tri-chlor tablets and not to worry about cyanic acid levels since hot tubs are usually covered and dont need to keep these levels up to protect from the sun. Help me out if you can. I always like to hear and learn more on water chemistry. I try to be as helpful and informative as I can to my customers.


First of all, you should not believe what anybody tells you, including what I tell you, without skepticism or questioning or verification until you feel comfortable you are getting all the facts and know the whole truth to the degree that it can be known. Second, you should review the many posts and threads in this forum, especially in this section on Hot Tub Water Chemistry. You should also take a look at two other forums, The Pool Forum which unfortunately is closed to new registrations and PoolSolutions and TroubleFreePool. Though these are not as focussed on hot tubs, the chemistry of the water is exactly the same. The differences between hot tub and pool water chemistry are related to 1) higher bather load in hot tub (much lower water volume and more sweat from higher temperature), 2) hot tubs are usually covered most of the time and not exposed to sunlight very much, 3) higher aeration due to jets, 4) higher water temperature and 5) hot tubs usually not having plaster/gunite/grout.

I do not work in the pool or spa industry and am just a homeowner with a pool who got frustrated years ago with problems with Trichlor and high CYA and decided to figure out the pool water chemistry (I majored in physics and chemistry in college but I have and continue mostly to work in S/W Engineering and related management). I learned a lot from the aforementioned websites plus my own theoretical investigations and validation against reports on multiple pool and spa forums, peer-reviewed scientific studies (mostly available on the Internet, but also troweling through university library archives), plus my own limited experience. There are quite a few people who know this chemistry and also respond on these forums, such as waterbear who also frequents this forum and knows far more about water testing and practical chemistry than I do. We're all just here to help each other and would welcome industry professionals (more on that later).

Chlorine is Chlorine

The first rule that you should have been taught is that chlorine is chlorine is chlorine, at least when it is in the water. The differences in the various sources of chlorine have absolutely nothing to do with differences of chlorine in the water. The chlorine that is produced in the water after such substances are dissolved is identical regardless of source. The differences between the sources of chlorine are 1) some add chemicals in addition to chlorine, 2) the pH can change differently depending on which source of chlorine is used, 3) some sources dissolve quickly while others dissolve slowly, 4) some are solid pucks or powder/granules while others are liquid or gas.

Now item #1 for the sources of chlorine is VERY important since the "extra" chemicals that come with the chlorine have significant side effects. But before we go there, let's talk first about bleach (or chlorinating liquid which is identical to bleach except for its stronger strength). The primary reason that bleach is not recommended (or voids the warranty) in a hot tub is that using ONLY bleach without any Cyanuric Acid (CYA) in the water (more on that later) would result in over-chlorination that would destroy the hot tub cover much more quickly. The other reason is that it is a liquid that can splash so if you are not careful then you can splash concentrated chemical onto surfaces, but realistically that can happen with any source of chlorine if you aren't careful. You should also add bleach (or chlorinating liquid) slowly over a return flow with the pump running (circulation on, but not jets since you don't want it splashed or aerated) since it is denser than water until diluted/mixed so you don't want it settling in concentrated form.

Differences in Chlorine Sources

It is an over-simplification that Dichlor holds up best when in the water. It is NOT the fact that the source of chlorine is Dichlor, but the fact that Dichlor contains an extra chemical (when dissolved in water), Cyanuric Acid (CYA), that is the reason it holds up best. It makes absolutely no difference whatsoever whether you add Cyanuric Acid directly to the water first (CYA is available in pure form without chorine) and then add bleach vs. adding Dichlor that contains both -- when dissolved in the water they produce IDENTICAL chemicals in the water (ignoring the extra sodium chloride salt in the bleach). If you add bleach with jets on then the chlorine might get aerated more and therefore outgas more than if you added Dichlor (since it does take dilution and mixing of the bleach with the water to get combined with the CYA that is in the water), but adding the bleach either pre-diluted or slowly with circulation and not jets should be similar to adding Dichlor. The pH is different, but I'll talk about that later.

When you add an amount of Dichlor that produces 10 ppm Free Chlorine (FC) in water, it also adds 9 ppm Cyanuric Acid (CYA).
When you add an amount of Trichlor that produces 10 ppm FC in water, it also adds 6 ppm CYA.
When you add an amount of Cal-Hypo that produces 10 ppm FC in water, it also adds 7 ppm Calcium Hardness (CH).
When you add unscented bleach or chlorinating liquid (both are sodium hypochlorite and differ only in strength) or Lithium Hypochlorite or chlorine gas to water, they do not add any CYA nor do they increase CH. The bleach, chlorinating liquid and lithium hypochlorite add 8 ppm sodium chloride (salt) for every 10 ppm FC and this is above and beyond the 8 ppm salt for every 10 ppm FC that is produced from ANY source of chlorine since the usage of chlorine produces chloride. Cal-Hypo adds somewhat less salt. Trichlor and Dichlor add no "extra" salt beyond that produced from the usage of chlorine.

The thing to keep in mind is that while chlorine gets used up and gets converted to chloride so more needs to be added, the CYA does not break down and just continues to build up as you add more products that contain CYA (e.g. Dichlor, Trichlor).

You can see this link for a cost comparison of chlorine sources.

Chlorine and Cyanuric Acid (CYA)

Though it is true that Cyanuric Acid helps protect chlorine from being broken down by the UV rays of sunlight, it is not true that this is its only side effect. The CYA protects chlorine from sunlight via two effects. One is a shielding effect since CYA absorbs UV so that lower depths of water are not exposed to as much UV when CYA is present. The other factor is that CYA combines with chlorine to form a series of compounds called chlorinated cyanurates, but are conceptually chlorine attached to CYA. These compounds are more resistant to breakdown from the UV rays of sunlight so this factor protects chlorine even at shallow depths. However, the chlorinated cyanurates are not effective sanitizers nor algaecides -- they are much, much more inert compared to chlorine that is unbound to CYA (specifically, compared to hypochorous acid). You can learn more about the chemistry of CYA and chlorine in this thread where you will notice that the equilibrium constants for the chemistry were known back in 1973 and published in 1974. Some manufacturers and others in the pool and spa industry deny that this chemistry has an effect in "real pools" and they refer to a study to back up their claims which I talk about in this thread.

You have no doubt heard that stabilized chlorine, that is chlorine in the water with CYA present, is less effective than chlorine without CYA and that high levels of CYA make chlorine even less effective. What you probably haven't been told is by how much. It isn't just a factor of two or so difference. It's orders of magnitude -- factors of 10 or more. This has not only been shown in numerous bacteria, algae, protozoan cyst studies, but also shows up in oxidation-reduction potential (ORP) which of course relates to oxidation and not disinfection. Though there is some variation in the studies in terms of higher CYA levels and disinfection rates, there is absolute consistency in higher CYA levels having lower disinfection and the difference between having CYA and not having CYA is huge. The disinfecting form of chlorine that is the most powerful is hypochlorous acid. If you look at the link I gave above on the chemistry of CYA and chlorine, you no doubt recognize the traditional industry graph of hypochlorous acid and hypochlorite ion at various pH, but this graph is very deceitful because it does not take into account what happens in the presence of CYA. At a pH of 7.5 with 30 ppm CYA in the water and a Free Chlorine (FC) level of 3.5 ppm, over 97% of the chlorine is attached to CYA while about 1.5% is hypochlorous acid and 1.5% is hypochlorite ion. Only the hypochlorous acid is the highly effective sanitizer and oxidizer and that is only 1.5% of what is measured as FC!

So what does this all mean? It means that if you use Dichlor every day in a spa adding, say, 4 ppm FC per day, then after 3 months you will have added 4*0.9*30*3 = 324 ppm CYA -- about 100 ppm CYA per month. This means that the chlorine in the spa becomes less effective over time. Though the biggest drop in chlorine effectiveness occurs with relatively small amounts of CYA (so basically after the first few days of Dichlor addition), after that the amount of disinfecting chlorine is roughly proportional to the ratio of FC to CYA. Roughly speaking, if you double the amount of CYA, you halve the amount of disinfecting chlorine (assuming constant FC). Another thing you were probably not told in your training is that the Free Chlorine (FC) test does not measure only the disinfecting chlorine (hypochlorous acid) nor the hypochlorous acid plus hypochlorite ion, but in fact it also measures the chlorine attached to CYA. This is because chlorine releases from CYA fairly quickly (the hydrolysis half-life of one chlorinated cyanurate species is 0.25 seconds while for another it's 4 seconds).

You might say, well since it gets released in the FC test, it must be effective for killing pathogens and preventing algae. That would be incorrect. The chlorine attached to CYA is like being held in reserve -- CYA essentially acts like a hypochlorous acid buffer. However, this reserve is not "active" and does not directly participate in the reactions that oxidize or disinfect (at least not to any great extent). The rate of chemical reactions is based on the INSTANTANEOUS concentration of the chemicals in the reaction, not on the amount in "reserve" that can be released more slowly by conversion of related compounds. The rate of killing pathogens, inhibiting algae and oxidizing organics and ammonia depends on the hypochlorous concentration. All the chlorine bound to CYA does is act as a reserve replenishing the hypochlorous acid as it gets used up -- so you don't run out of chlorine as quickly, but it does NOT speed up the chemical reaction. It's like having a large army reserve without rifles and having a much smaller number of active soldiers with rifles. The rate of killing is dependent on the number of soldiers with rifles -- the reserve just means that when such active soldiers get killed that new ones can take their place from the reserve (that is, the rate of killing tends to remain constant instead of slowing down if active soldiers get killed, but the overall rate of killing is far, far less than if all soldiers were "active" instead of mostly being in "reserve").

If you don't have any CYA in the water at all, then adding even small amounts of chlorine produces a LOT of disinfecting chlorine (hypochlorous acid) and essentially you over-chlorinate the water. This is, in effect, what happens in most indoor swimming pools since CYA is not used in that water and it is annoying as hell since my wife's swimsuits degrade (elasticity deteriorates; they are fade resistant so only fade a little) over just one winter season of use in an indoor pool while in our outdoor pool that has CYA her swimsuits only show very slight signs of wear after 4 summers of use. Her skin and hair are also much more affected by the chlorine in the no-CYA environment. In fact, I believe that many of the problems with asthma and respiratory problems with indoor pools are not just due to poor air circulation and lack of sunlight, but also due to not using CYA (or using too much CYA which has different problems) since higher chlorine levels produce more disinfection by-products -- a fact well-known in the water treatment industry. I haven't proven this with real-world data and only have breakpoint chlorination models that indicate this, but there is a study in Europe that I've told to look at CYA levels as a factor and hopefully they will do that. It is the industry mantra that "CYA only protects chlorine from sunlight so isn't needed in indoor pools" that has led to these practices. At the other extreme, the industry mantra that "CYA doesn't matter; only FC matters" has many outdoor pools develop algae when Trichlor is used over time without additional algaecide or increase in FC level to match the rising CYA level.

So no CYA is bad because the disinfecting chlorine concentration is too high and too much CYA is bad because the disinfecting chlorine concentration is too low, so how much is really needed? We don't really know for sure, but from the data from thousands of multiple pool and spa forum users plus disinfection (CT) rate data it appears that very low disinfecting chlorine amounts are needed to kill most pathogens, but higher amounts may be needed to prevent hot tub itch and certainly higher amounts are needed to prevent algae growth (mostly in pools since spas generally don't get enough sunlight for algae to be a problem). The rough rule of thumb is that, without an algaecide (or phosphate remover), you need a minimum FC level of 7.5% of the CYA level to prevent algae growth, at least up to phosphate levels of 3000 ppb or so (above that, it might make more sense to use a phosphate remover unless higher FC levels are maintained). Pools that have extra systems such as saltwater chlorine generators (SWG) can usually get away with an FC level of 4.5% of the CYA level to prevent algae (due to superchlorination in the SWG cell that helps kill free-floating algae). To prevent hot tub itch in spas, I've been recommending 4 ppm FC with 20 ppm CYA so a 20% ratio, but that may be too conservative and perhaps 50 ppm CYA might be OK, but we don't have enough data yet to know. Certainly, 100+ ppm CYA is going to not be sanitary enough even with the more reasonable (lower) CT values of some pathogens (though some others are very easy to kill even at 100+ ppm CYA). And besides, it makes absolutely no logical sense whatsoever to vary the disinfecting chlorine level over the 3 months one uses a hot tub. Finally, high levels of CYA and therefore low disinfecting chlorine levels also slow down the breakpoint reaction of chlorine with ammonia so one finds more Combined Chlorine (CC) if you don't keep the CYA level in check.

To get to 20 ppm CYA in a hot tub, you would add Dichlor at a rate of around 4 ppm FC (2 teaspoons in 350 gallons) per day for about a week and then switch to unscented bleach (3 fluid ounces of 6% bleach in 350 gallons) after that, assuming that chlorine usage is around 4 ppm FC per day on average.

Chlorine and pH

Now let's turn to pH. It is generally recommended NOT to use Trichlor in hot tubs because Trichlor is highly acidic. It's bad enough in pools, but in spas the acidity can be more harmful, mostly because the water volume is much lower so you can make a mistake and get the pH too low much more easily. One of the myths in the industry, however, is that Dichlor is pH neutral (or nearly so) and that bleach or chlorinating liquid are high in pH. Though this is technically true, it is deceitful and misleading because it does not account for what happens when the chlorine then gets used up. I talk about this in the chemistry link I gave earlier, but essentially the breakdown of chlorine (by sunlight, disinfection or oxidation) is an acidic process that almost exactly compensates for the initial rise in pH from bleach or chlorinating liquid addition. When taking this into account, Dichlor is actually acidic and Trichlor is very acidic while the hypochlorite sources of chlorine (bleach, chlorinating liquid, Cal-Hypo, Lithium Hypochlorite) are close to pH neutral.

So you might ask, why does the pH rise if I use bleach? The reason is that the pH rises is that pools and spas are intentionally over-carbonated and this excess of carbonates (which is most of what is measured in Total Alkalinity, TA) outgasses as carbon dioxide. When this happens, the pH rises (with no change in TA for technical reasons I won't get into here). The relative rate of outgassing of carbon dioxide is a function of pH and TA as shown in this table where you can see that the rate is higher at lower pH and higher TA. The rate is also higher when there is more aeration, so when running the jets. The procedure to lower the TA level therefore takes advantage of these facts by adding acid in conjunction with aeration all done at low pH as described in this post. If you use a lower TA below 80 (but above 60 in spas and 50 in pools) and target 7.7 as a goal pH, you can significantly reduce the rate of pH rise. Or you can just not aerate and use a cover more frequently, but for spas aeration (via jets) is part of the experience.

[EDIT] Also, there is an initial rise from bleach addition and until the chlorine gets consumed (FC drops) the pH will be high so one should start at a pH of 7.5 before doing bleach addition or one should add acid and then bleach to more closely simulate what occurs with Dichlor (minus the added CYA). [END-EDIT]

What You Can Do

Thank you so much for asking questions and wanting to be helpful to your customers. I'd like to educate the resellers and retailers since it seems to me that the manufacturers are not doing so, but when I've approached these groups (both manufacturers and retail chains), including trade groups like the APSP, I generally get rebuffed or ignored (if not at first, then after some correspondence). I don't mind if they want to present their opinions along with the data I present, but I'd at least like to make sure you have all the information you need to help your customers. So to the extent that you can go back to your training instructors and industry professionals and start questioning them about this stuff, then maybe there will be some positive movement towards more thorough education.

Richard

#2 104 Degrees

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Posted 12 January 2008 - 03:07 PM

Richard

I'm going to switch to Bleach tomorrow.I dumped the tub at the end of dec.It looks like the spa makers are making alot on the dichlor and dont want to lose anything with the easy to get and cheaper Bleach????


I'll get back to you.John
Happiness is having your hot tub Spike to 105 Degrees when it's -20 outside. Nordic Crown Xl Owner

#3 chem geek

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Posted 12 January 2008 - 03:32 PM

John,

Don't panic or anything like that. As you can tell from reading the many posts on this forum, the number of people that have problems with their spas using Dichlor alone even every day for 3 months is minimal. It just doesn't make logical sense to have varying disinfection or breakpoint oxidation throughout the period of usage and that's the primary motivator for stopping at some CYA level or even adding some CYA to start with at the beginning. Technically during that first week and especially the first days after a fresh refill, you're exposed to more chlorine than you'd normally want to be, but it's not horrible and one could have a regimen of a super-shock right after a fresh refill for a couple of days and then let the chlorine drop as that would give a quick initial CYA boost without needing to buy pure CYA (which dissolves very slowly). There is no proof that the hot tub itch scenarios are due to low disinfecting chlorine concentration -- we've had too few incidents (about 7 now, if I count correctly) to know for sure if that's the only cause, but it is true that in every case it either happened after at least 1.5-2 months of Dichlor use or in the first month with some zero chlorine time (from MPS daily; chlorine only weekly use).

I don't think the push for Dichlor is so simple to explain. Bleach is a liquid that is much easier to spill and bleach clothing than powdered Dichlor, though spilling the powder ain't so good either. As you could tell from the initial questions I got, dealers are TAUGHT to use Dichlor and I don't think the manufacturers do that because of profit since spa makers don't make Dichlor. It's that using only bleach without any CYA in the water is harmful to their spas or covers -- they are legitimately pointing out a problem. It's just that it wasn't thought through -- they said "don't use bleach so only use Dichlor" -- instead of thinking that a proper BALANCE might be the best approach. There is a post somewhere on this forum from a hot tub manufacturer that ranked cover life vs. different sanitation methods and it pretty much lined up with the amount of chlorine in the water -- if there were bleach-only with no CYA in the list, it would have been way, way worse than anything that was listed.

This isn't the spa makers fault since they don't generally know enough about water chemistry to make such decisions, but the manufacturers of Dichlor, Trichlor and specialty chemicals do know such things, or at least should if they are competent. I think the more telling scenario is with pools since there the problems of CYA are much, much more apparent since algae develops in many, many pools when the CYA keeps climbing while the FC is kept relatively low at the recommended 1-3 ppm range. The manufacturers DO sell "programs" that include algaecides, but they don't tell retailers and pool stores WHY it's needed -- namely that it is the CYA in the Trichlor tabs that builds up that causes the problem. If they told that truth, then the manufacturers may fear that the retailers might not push selling Trichlor as much, but I think that's not what would have happened since they could have just told pool owners the truth that an alageide is required and why. Chlorinating liquid is a pain for most people and even when you automate its dosing you still have to buy it regularly so many people, I think, would have continued to use Trichlor but at least would have known why an algaecide was also required and not think that it was just the pool store pushing it for more profit -- instead, there were clear technical reasons needed for it. The irony is that Trichlor sales are significantly down because most new pools today have saltwater chlorine generators (SWG) so now all that some of the manufacturers have really done is created an industry of distrust.

Even some of the SWG manufacturers are playing the same game since they aren't fully disclosing about potential problems with salt (see this link for more extreme examples and realize that most SWG pools in many areas don't have these problems, at least not as quickly, but there is no question that salt is more corrosive and that proper materials need to be used -- just as is done because chlorine itself is corrosive and is why you use stainless steel and not plain steel nor zinc in pools -- I also have a technical discussion about this in this thread).

I don't know why but the pool and spa industry seems to be behind many others in terms of the maturity that goes along with being honest with your customers in order to develop long-term relationships and win-win scenarios. There is this fear that telling the truth will hurt sales or drive one to use another's product, but that is truly insulting to people since it assumes we're all so stupid as to not be able to handle fully disclosed pros/cons and make intelligent and rational choices. Some day, I hope this will change. There are certainly a lot of good folks out there and not all manufacturers, distributors, dealers, stores, pool builders, etc. are alike.

Richard

#4 104 Degrees

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Posted 12 January 2008 - 03:45 PM

I was biggrin.gif kidding about the Bleach.They may not make it,the dealers sell it wink.gif

John
Happiness is having your hot tub Spike to 105 Degrees when it's -20 outside. Nordic Crown Xl Owner

#5 greenworks

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Posted 13 January 2008 - 03:07 PM

Great post Richard

as a new guy around here if I would have seen this thread it would have saved the 10+ questions I asked as I couldn't find all this in one nice article. to the admin guys here could we make this post a sticky so newbies are seeing it right away it would save alot of work for Richard & water bear answering the same questions daily, and then free them up for weird and unusal water issues...

Just my opinion however it just that many sites I frequent attach high usage questions in a sticky at the top of the appropiate forum to save repetive posts.

Jason

#6 waterbear

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Posted 14 January 2008 - 10:33 AM

Richard,
An excellent answer. I also think it should be made into a sticky!

IMHO, the reason that dichlor is recommended is because dealers sell it and many manufacturers distribute it. There is clearly a profit motive here. It has a very long shelf life compared to other forms of chlorine that are suitable for use in a spa (trichlor is not). However, in some states dichlor is outlawed in commercial spas so only liquid chlorine (bleach), cal hypo, or lithium hypochlorite (the three unstabilized chlorines and the only other forms suitable for spa use) are permitted. Makes you wonder, doesn't it?
I've tested more water than I ever care to think about!
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#7 104 Degrees

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Posted 14 January 2008 - 10:47 AM

QUOTE(waterbear @ Jan 14 2008, 11:33 AM) <{POST_SNAPBACK}>
Richard,
An excellent answer. I also think it should be made into a sticky!

IMHO, the reason that dichlor is recommended is because dealers sell it and many manufacturers distribute it. There is clearly a profit motive here. It has a very long shelf life compared to other forms of chlorine that are suitable for use in a spa (trichlor is not). However, in some states dichlor is outlawed in commercial spas so only liquid chlorine (bleach), cal hypo, or lithium hypochlorite (the three unstabilized chlorines and the only other forms suitable for spa use) are permitted. Makes you wonder, doesn't it?




Happy New year Waterbear biggrin.gif wink.gif

John
Happiness is having your hot tub Spike to 105 Degrees when it's -20 outside. Nordic Crown Xl Owner

#8 TinyBubbles

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Posted 14 January 2008 - 01:49 PM

The issue of warranties being voided due to the use of bleach is brought up alot. If chlorine is chlorine, can a manufacturer prove if bleach was used in a spa?

#9 tony

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Posted 14 January 2008 - 05:39 PM

QUOTE(TinyBubbles @ Jan 14 2008, 04:49 PM) <{POST_SNAPBACK}>
The issue of warranties being voided due to the use of bleach is brought up alot. If chlorine is chlorine, can a manufacturer prove if bleach was used in a spa?


As long as you keep your pH and TA in line.......they can't.

#10 B0Darc

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Posted 15 January 2008 - 08:24 AM

QUOTE(TinyBubbles @ Jan 14 2008, 03:49 PM) <{POST_SNAPBACK}>
The issue of warranties being voided due to the use of bleach is brought up alot. If chlorine is chlorine, can a manufacturer prove if bleach was used in a spa?

I recently installed a new toilet and the sticker on the bowl said not to use bleach or chlorine based products to clean or it would void the warranty (?!?!) Doesn't this all sound like an automatic out come warranty claim time? I think it speaks more to the destructive nature of what can happen with liquid Chlorine regarding spills and how easily you can overdose. The powdered forms are safer for obvious reasons, but canceling warranties is ridiculous. I guess the message is hide all bleach bottles when you have to call the dealer or Spa Tech, and confess NOT your sins wink.gif



#11 chem geek

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Posted 15 January 2008 - 10:55 AM

Like much in life, moderation is important. The toilet manufacturers just put a blanket no-no to chlorine because putting in a tablet with chlorine into the toilet water (or adding bleach) will often produce very high chlorine levels. Because there is no CYA to moderate the chlorine level, it's pretty darn high and that's corrosive to metal and rubber seals. Even if you put a paperclip (usually zinc coated) into pool water, it will show corrosion in a few days even at relatively low chlorine levels with CYA. This is why stainless steel is used in pools instead of regular steel or zinc-coated materials.

In a toilet bowl, sanitation doesn't have to be immediate. I suppose someone could come up with a silver product for that purpose, but realistically people get overly concerned with bacteria in these environments (unless they are talking about public restrooms in which case person-to-person transmission is more of an issue). There is far more bacteria in most kitchen sponges than in a toilet bowl. It has more to do with the bacteria having food sources as well as moisture in order to grow. Besides, one expects to have bacteria in a toilet. It's when preparing food that there should be more concern -- at least for uncooked foods like raw or lightly blanched vegetables. Nevertheless, food poisoning isn't that common in homes in spite of the relatively poor sanitation practices during food preparation (most foodborne illness likely comes from contaminated food prior to distribution rather than inadequate sanitation during preparation at home).

Richard

#12 David G

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Posted 15 January 2008 - 06:30 PM

Richard,

As a newby to the board and a relatively new spa owner your post was a major education. I too think it should be made into a sticky!

My question relates to frequency of adding the bleach. I travel a lot in my job so it is impossible to add bleach on a daily basis. I am generally home by Friday night and the spa often only gets used Friday and on the weekend. Since inheriting the spa from the previous home owner I have been using pucks and now the Beachcomber sticks in a floater plus a granular dichlor for shock. After 6-8 weeks I am finding that my reading of TCI eventually goes through the roof even when my FCI is at or below 3 ppm. I assume that this is due to excess levels of CYA. My dealer did a CYA test a couple of weeks ago and it was through the roof - just over 120. I have now changed the water and done an initial shock with dichlor and have had the floater in the water for a week but would now like to switch to bleach before CYA gets high again.

Also I am currently using test strips but would like to switch to the more accurate test kit. I have seen a recommended brand on the board but did not record it. Could I have your suggestion ?

Thanks to all contributors, one evening on this board teaches me more that my well meaning dealer has in 6 months of ownership.



#13 chem geek

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Posted 15 January 2008 - 09:19 PM

That's a tough one because with chlorine there isn't a slow-dosing automatic mechanism available for spas though you will see some recent posts talking about various possibilities for automatic dosing. In pools, one can hook up The Liquidator talked about in this thread. Other options are peristaltic pumps, but no one has tried these solutions for a hot tub (that I'm aware of). Another option is to have a partially open jug of chlorine bleach, open-side up, but we haven't figured out the amount it needs to be open yet and you have to make sure there is some circulation at some times and that the jug doesn't tip over, etc. To avoid the frequent dosing, many people use bromine instead since you can have a floating feeder that lasts around a week. With chlorine, Trichlor could be used in pools (not all the time, but for vacations, business trips, etc.) but it's too acidic for spas, probably dissolves too quickly, and adds to CYA besides.

Another option for you would be to use a less-than-ideal (by itself, that is -- they are fine with chlorine) disinfectant for the time you are away. So perhaps a metal ion system (silver, such as Nature2) which is slow-acting, but is probably good enough while you are away. Then, shock as soon as you get home with some chlorine, let it dissipate a bit, and you should be fine within 30 minutes to an hour at most as far as disinfection is concerned (probably fine in 5-10 minutes, but I'm being conservative). Other slow-acting options would be PolyQuat 60 algaecide which is also a clarifier and also slowly kills pathogens, but isn't advertised as such since it is slow-acting. Even MPS oxidizes some pathogens slowly, but it doesn't last very long so the PolyQuat is a better bet. If you had an ozonator, then that would also be something that could run while you were out. Having any of these -- silver, PolyQuat, ozonator -- will keep your spa in halfway decent shape until you get home and give it a fast-kill with chlorine.

Yes, the high CYA level would make breakpoint of monochloramine (chlorine plus ammonia) slower -- probably 5 hours or longer -- but the problem could also just be not enough chlorine to keep up with demand though you wouldn't be registering any FC in that case. One can use MPS to help oxidize the organics if you want, but one should be able to use mostly chlorine to handle the tub.

The normally recommended test kit for chlorine is the Taylor K-2006 that can be bought for a good price here. Another option is the TF-100 kit from tftestkits.com here which has 36% more reagents so is roughly equivalent in price per quantity and is based on Taylor reagents but with more logical quantities (and the CYA test goes down to 20 instead of 30, though it does not have acid/base demand tests that usually aren't needed, and it also comes with an OTO chlorine test in addition to the FAS-DPD test).

Richard

#14 waterpen

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Posted 11 July 2008 - 08:52 PM

QUOTE(chem geek @ Jan 15 2008, 09:19 PM) <{POST_SNAPBACK}>
That's a tough one because with chlorine there isn't a slow-dosing automatic mechanism available for spas though you will see some recent posts talking about various possibilities for automatic dosing....With chlorine, Trichlor could be used in pools (not all the time, but for vacations, business trips, etc.) but it's too acidic for spas, probably dissolves too quickly, and adds to CYA besides.


This is interesting because I just got my Beachcomber hot tub and the chemicals that came with it included a puck dispenser and trichlor mini-pucks. The recommended routine is to use the puck (trichlor) to automatically dispense the sanitizer, then use CareFree Boost (Dichlor) as the shock when needed, and CareFree (MPS) as the weekly oxidizer.

From reading this forum, it seems the the main issue with trichlor is that it is acidic and will cause a ph drop. Of course it also adds CYA, but so do other forms of stabilized chlorine (e.g. dichlor).

Any thoughts from the water chemistry pros? biggrin.gif

By the way, the pail of pucks says "Trichloro-s-triazinetrione", which I assume to be trichlor - is that right? unsure.gif

#15 chem geek

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Posted 12 July 2008 - 12:17 AM

Yes, that's Trichlor. It has the advantage of adding less CYA for the same amount of FC than Dichlor. For every 10 ppm FC added by Trichlor, it increases CYA by 6 ppm while with Dichlor that same 10 ppm FC will add 9 ppm to CYA.

The main problem is the high acidity of Trichlor. It's not impossible to use, you just have to be very careful with it. For safety, the TA level should be higher -- in the 120-140 ppm range or maybe even higher depending on the amount of aeration (more aeration won't need as high a TA).

I don't see any need for the CareFree Boost (Dichlor) though I suppose that's to rapidly increase the FC level with less of an effect on the pH. If you can maintain the FC level consistently, then you shouldn't need to shock much at all and if you do, then MPS should do the trick.

As examples of what might happen with pH, consider a spa with 80 ppm TA and using Dichlor at a rate of 4 ppm FC per soak in 350 gallons (so one person for 30 minutes). That's about 2 teaspoons of Dichlor and its addition and chlorine usage results in a pH drop from 7.5 to 7.37. If there was aeration for carbon dioxide outgassing, then let's say there was enough (2.7 ppm TA equivalent) to have the pH remain at 7.5 (we'll then compare this to Trichlor).

If you used Trichlor at the same 80 ppm TA level, then this would be 0.2 ounces weight of Trichlor which would lower the pH from 7.5 to 7.32. If there was the same aeration as above, then the pH would drop to 7.44. If the TA were higher at 140 ppm, then there would be more outgassing and the pH might be more neutral.

So it's not a disaster to use Trichlor but you just have to be a little more careful. The biggest thing to watch is where those packets go since the area around them will get very acidic so keep it away from metal or the edge of the spa if possible.

Richard

#16 waterpen

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Posted 12 July 2008 - 03:05 AM

QUOTE(chem geek @ Jul 12 2008, 12:17 AM) <{POST_SNAPBACK}>
Yes, that's Trichlor. It has the advantage of adding less CYA for the same amount of FC than Dichlor. For every 10 ppm FC added by Trichlor, it increases CYA by 6 ppm while with Dichlor that same 10 ppm FC will add 9 ppm to CYA.

The main problem is the high acidity of Trichlor. It's not impossible to use, you just have to be very careful with it. For safety, the TA level should be higher -- in the 120-140 ppm range or maybe even higher depending on the amount of aeration (more aeration won't need as high a TA)....

If you used Trichlor at the same 80 ppm TA level, then this would be 0.2 ounces weight of Trichlor which would lower the pH from 7.5 to 7.32. If there was the same aeration as above, then the pH would drop to 7.44. If the TA were higher at 140 ppm, then there would be more outgassing and the pH might be more neutral....


Thanks Richard!!! Excellent information. Yes, Beachcomber's guidelines say TA should be arounf 120, so it confirms your advice. We will likley use aeration on the jets all the time, so that should produce more outagassing and help to keep the ph towards neutral.

We have the new UV sanitizer sytem (made by Delta), so the dealer said that should decrease the trichlor use, and set the puck dispenser at a lower amount. Hopefully that will also help keep the ph more neutral.

The test kit supplied by Beachcomber has the (Taylor) DPD reagents for chlorine and a ph indicator solution. So I will have to take the water sample into the dealer to check other parameters, including TA.

Will know more in a few weeks...

By the way, the webpages for the links to the K-2006 and TF-100 test kits from an earlier post in this thread indicate that they no longer ship to Canada sad.gif . Does anyone know a good source for these kits in Canada? Some earlier threads were putting the price of a Taylor k-2006 kit at $199 !!! wacko.gif Has anyone found a decent Canadian source and price since those posts??

#17 chem geek

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Posted 12 July 2008 - 09:11 AM

Unfortunately for Canada Taylor has an exclusive distributor so the price is high from any retailer in Canada. If you're near the border with the U.S., you can drive over here to get it (though most stores don't carry it so you'd have to have one pre-order it and hold it for you) or you can have a U.S. friend buy it and ship it themselves to you (though it may get held up or have extra charges in customs). If you buy your K-2006 kit in Canada from Apollo Pools shown here, then you get a free magnetic stirrer with it and that makes its $169 CAN price more reasonable since the stirrer is a good value.

For the spa situation you described, just keep an eye on the TA level as it will go down over time via the aeration and acid addition (from the Trichlor). If the pH is OK but the TA is low, you can use Arm & Hammer Baking Soda to raise it. If both the pH and TA are low, then you can use Arm & Hammer Super Washing Soda (careful: NOT the detergent) to raise both. The better situation is to have the TA high enough so that the outgassing ends up keeping the pH stable and only the TA drops -- that way only baking soda will be needed on occasion.

Richard

#18 waterpen

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Posted 12 July 2008 - 12:00 PM

Thank you Richard! biggrin.gif

#19 Nitro

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Posted 03 March 2009 - 09:46 AM

I'm bumping this thread, because it needs to be.
Nitro's Approach To Water Maintenance
A guide to Water Balance and Sanitation using Chlorine

Lowering Total Alkalinity
How to lower TA, without lowering pH

Chlorine Demand (CD)
What is it, and why you should care

Decontamination
How to Super Shock your Tub

#20 denvertub

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Posted 03 March 2009 - 08:21 PM

"To get to 20 ppm CYA in a hot tub, you would add Dichlor at a rate of around 4 ppm FC (2 teaspoons in 350 gallons) per day for about a week and then switch to unscented bleach (3 fluid ounces of 6% bleach in 350 gallons) after that, assuming that chlorine usage is around 4 ppm FC per day on average."

Question regarding the amount of chlorine. I've got a 500 gal. tub and I'm curious about the average free chloring usage. With our tub it's usually one or two people a day for about 15-30 minutes on average. I've been adding approximately 4oz of bleach per day but I'm keeping my fc level at about 1-3 ppm and sometimes even closer to zero. What are others experiencing with regard to the specific amount of bleach to add per day. Should I still add 4oz on days where we do not use the tub at all.... Should I be adding a percentage more than 4oz on days we do use the tub?

Thanks

#21 chem geek

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Posted 03 March 2009 - 11:31 PM

Roughly speaking, at hot tub temperatures, it takes around 7 ppm FC in 350 gallons of chlorine per bather hour to oxidize the bather waste (ammonia and urea from sweat and urine). Your usage would be around 15/60*7*350/500 = 1.2 ppm FC to 4.9 ppm FC per day depending on the number of people and length of soak as you indicated. The 7 ppm FC is dependent upon tub size, so perhaps a better rule which is independent of tub size is 5 fluid ounces of 6% bleach (or 3-1/2 teaspoons of Dichlor) per person-hour of soaking. So that's 1-1/4 fluid ounces to 5 fluid ounces per person-hour of soaking. Your 4 ounces should add slightly less than 4 ppm FC to your 500 gallon tub.

It sounds like you've got a higher chlorine demand than one would expect when you aren't using the tub, but you can get a feel for that by seeing your chlorine demand as Nitro described here. You just want to add enough chlorine to make sure you don't get to zero -- you want at least a small residual at the start of your next soak. Perhaps during some soaks you are getting a little behind.

Richard




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