What is the actual effect of iso-cyanuric acid (CYA) stabilizer on chlorine in an uncovered outdoor home pool

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not so, I've used powder and pucks for 22 yrs with no problems and have *never* added liquid chlorine. i think you're way over thinking this issue and making it way more complicated than it needs to be. jmo
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ChairMan wrote, on Sat, 28 Jun 2014 19:18:03 -0500:

There's no way that can happen "if" you're *not* at the same time diluting the water. It's impossible otherwise for it to make any sense to use pucks and/or powder.
By all accounts, only one of two things can happen if you use powder and/or pucks, and this is something that *everyone* agrees upon, from health organizations to pool companies to pool stores to all homeowners who have read the literature.
1. You use powder & or pucks BUT you *also dilute* periodically a huge amount of water (typically 1/3 of the pool or so), either accidentally (e.g., rain, leaks) or on purpose (e.g., drain & refill).
Or
2. Your cyanuric acid levels will eventually climb over 100 ppm, and you will be in a never ending battle with chlorine as it just won't be effective at that level of CYA.
All agree, there are no other possibilities than those two, and the second is terrible, so, in the end, you *can't* use powder and/or pucks forever *unless* you periodically dilute the CYA in the water.
Note: There are chemical ways to reduce CYA (e.g., melamine), but, pragmatically, simple dilution is the standard approach.
Of course, there will always be someone who says that CYA levels over 100ppm don't debilitate the chlorine, e.g., http://www.aquaticspecialtyservices.com/msds/Techbulletin1.pdf but, it seems it's always the ORP salespeople who spread the most FUD about this, which all the health departments are in agreement (100 ppm CYA is generally the legal limit).
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On Sunday, June 29, 2014 12:21:16 AM UTC-4, DannyD. wrote:

For many of us in the climates where it freezes during winter, that dilution comes from winterization and reopening. You typically pump the pool down below the skimmers to winterize. Then if you have a cover that water flows through, it fills all the way up with rainwater over the winter. In the spring you have to lower it to the normal level. That plus backwashing, is enough to keep it in line.
Also, consider that because of your high targets for chlorine, which are 3 to 4X those of the rest of us, you're adding those tablets at a horrendous rate. And each tablet brings with it more CYA and then you raise the chlorine target even higher, and then add even more tablets. It's a tiger chasing it's tail. With 4 floaters, a chlorine target of 8ppm, I'd have a CYA problem too.
What CYA levels most people wind up with, IDK. But I think what Chairman is saying about people just using the tablets is true. Most probably don't even know what their CYA level is. And it apparently isn't leading to health problems, green pools, etc. ie it sure seems to work without raising chlorine to 8ppm. That's the one thing that I have not seen anyone do, that I know of ever. Everyone keeps chlorine at 1 -3 and it works.
As a side note, it's also interesting that AFAIK, they don't sell tablets without the CYA. I would think they would, because if you're CYA is at the right level, then you could buy that product, which is the cheapest, easiest form and not diminish the effectiveness of the chlorine. But again, the fact they don't is probably another indication that people are just using it like Chairman says, ie, keep using the tabs, they probably don't know what their CYA even is, and it apparently isn't creating big problems, health issues, etc.
It seems you have two choices. Obsess about CL/CYA and spend 4X the money that most of us do, or do what we do and which apparently works.
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Of course the water gets diluted, by rain, evaporation, vacuuming, and backwashing. Between all of those, I'd say my pool gets at least a third of its water replaced each year. Hell, around here, I can lose a half inch a day just from the wind and evaporation. I don't know what I'm doing that is so different that anyone else, but I know I 've never had an issue.
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trader_4 wrote, on Sun, 29 Jun 2014 04:16:43 -0700:

Hi Trader,
That's a good point, as, you do seem to understand this better than I do. As long as you dilute the water (winterizing is good), then you can use the pucks/powders forever.
The person I was responding to in my prior post had suggested I was "overthinking" the FC:CYA ratio, and I simply wanted to make sure he wasn't "underthinking" it.
If he's "winterizing" that way, then he's ok; but if he's not diluting the water, he can't use those pucks/powders forever.
At the pool store last week, a guy came in with CYA levels that were so high, the clerk titrating his water shook his head, saying his CYA was off the scale. The customer said he used the trichlor pucks for 3 years but now he can't keep the algae in check.
I explained to him "no wonder", and he complained that it would cost a lot of money to drain his pool - and I told him he really had no choice. He was underthinking the problem.

After reading all your posts, and fully understanding your point, I have already removed three of the four floaters (I left one in the hottub because it has a different flow characteristic for the self-cleaning pool).
You have helped me change my mind. In fact, you and I agree on all points save one. And, that one is in your favor as I could not find a *single* health department that backed up the 10% FC:CYA ratio that I was subscribing to earlier.
So we agree on standards: a) No health department prescribes the combined FC:CYA ratio b) All health departments specify separate FC minimums & CYA maximums
And, we agree on basic pool chemistry of: c) Tablets/powders add CYA so water *must* be diluted (eventually) d) FC at very low levels works just fine (CYA notwithstanding) e) CYA has "some" detrimental effects on FC effectivity
The only difference of opinion we have is how much credibility we grant to the outspoken proponents of the 10% FC-to-CYA ratio.
As you probably know, I've had concurrent personal Internet conversations with Richard Falk, who is a proponent of the ratio, where he, at least, justified his assertions when I asked him for details (e.g., he was who told me about the ORP (redox potential) measurement inaccuracies).

While I agree with you that most people don't have a clue about CYA, (and so do the health department advisory PDFs that I shared with you), I consider that to be "underthinking" the problem.
Every pool owner should know at least these two things: 1. How much CYA is in the pool, and, 2. Are they adding/diluting to that level.
If they're adding, they *will* have a problem (e.g., algae).

Actually, it is. http://www.troublefreepool.com/content/126-defeating-algae
The problem is that those who underthink the problem are the ones who use algacides and lanthanum chloride phosphate removers.
By underthinking the problem, they've allowed the enemy to take hold, where they then compound their underthinking error by fighting that enemy with the wrong tactics.

While I understand your point that people keep chlorine far lower than I do, at least you understand that I am approaching this from a target dynamic FC-to-CYA ratio (of about 10%), and not from the too simplistic static FC concentration alone.
Also, you'll note I have no need for shocking, and, that I don't have algae at the moment (I do get algae in the winter but that's due solely to strategic lax maintenance on my part).
You'll also note that I have high sun loads, as living on a mountain affords my pool zero shade and 100% sun, dawn to dusk.
And, you'll note, that TONS of people *do* have problems because of the use of tablets/powders; they just underthought the problem, so they can't figure out why: http://www.troublefreepool.com/threads/51606-Tablets-and-CYA

I agree with you! Why don't they sell tablets w/o CYA? Must be that they can't do that, but, the fact that more than half the tablet & powder *is* CYA is a big negative to these products! http://www.poolforum.com/pf2/archive/index.php/t-21810.html?s/20802eccb6db67e1273fe140d47a86

I agree that most people are, like Chairman said, not even *thinking* about their CYA levels, and certainly not the *ratio* of chlorine to cyanuric acid.
You also have to admit a few more things: a. Many people shock their pool (why? There's no need.) b. Many people have algae & clarity problems (again, why?) c. Many people use algacides (why? Never is it needed) d. Many people use phosphate removers (again, why?)
So, while I can't speak for those who underthink the problem, I suspect they are clueless that tablets/powder is more than half CYA. If they are accidentally lucky, they are diluting that CYA (either by winterizing, or by rainfall, or by refilling after leaks/evaporation, etc.).
However, if they're *not* inadvertently diluting that CYA, then they *will* (eventually) have a need to shock the pool and/or attack algae.
When you logically think about it, there is no other possible flow diagram of what *will* happen if/when they allow their CYA to go off the charts (assuming no inadvertent dilution).

Well, I/you have many choices, but, what I choose to do is to: a) Remove the floaters (this thread has proven the need for that!) b) Add FC in a 10% ratio of FC-to-CYA (I understand the debate here) c) Maintain my pH a little lower (after having read the PDFs in this thread) c) Never shock (there's no need to shock, ever!) d) Never add phosphate removers (even though my phosphates are very high) e) Never add algacides (free chlorine *is* an algacide)
Thinking about the problem, the only pool chemicals I plan to buy are: a) Liquid chlorine (yes, it's an expensive pain; but it's zero CYA) b) Muriatic acid (my well water has a high total alkalinity)
I plan to target a FC-to-CYA ratio of 7.5% (realistically ~10%) at nightfall so as to give the chlorine all night to work (which will then diminish during the day due to copious direct sunlight).
So there are three choices for all pool owners: a) underthink the problem b) overthink the problem c) understand the problem
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DannyD. wrote, on Sun, 29 Jun 2014 14:12:53 +0000:

BTW, I forgot to mention that he left the pool store with his arms full of both lanthanum chlorides and copper sulphates!
Heh heh ... that's what happens when you underthink a problem!
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On Sun, 29 Jun 2014 14:12:53 +0000, DannyD. wrote:

You guys are both saying the same thing in different ways.
I don't know what your stabilizer level is but if it is around 20 where it should be then you are keeping your chlorine at 2 which is where trader says it should be.
Its only if your stabilizer is high that you guys slightly diverge.
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In belched:

I''m not underthinking it. I just know what works for me. I don't use *any* chlorine from Nov- April depending on the weather. All i use is phosphate remover and continue running the pump. Once the swimming season starts, I test and add what ever is needed to get things where they need to be. Which may be just some shock and soda ash. My water stays clear all winter
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In belched:

I take my water in a couple of times during the swimming season to Leslies and have them run the full spectrum of tests. Like I said CYA has *never* been an issue
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ChairMan wrote, on Sun, 29 Jun 2014 16:26:16 -0500:

Hi ChairMan,
I don't use any chlorine in the winter either, but, in my case, the pool turns into a swamp without chlorine, so I drain, hose down, and refill - and then it's crystal clear again.
I understand your philosophy on the phosphate remover, which is that algae can't grow without phosphate. That lanthanum chloride flocculates the phosphates onto the bottom of the pool, so, are you vacuuming up the debris during the winter?
If I could find an industrial source of rare-earth chlorides, I might approach my pool the same way you do yours, this coming winter, and see how it works for me (we have warm winters though, in California, in the 60's & sometimes getting to 80 degrees).
Thanks for the hints!
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ChairMan wrote, on Sun, 29 Jun 2014 16:29:25 -0500:

I run mine at least once every two weeks through Leslies, and often weekly, since it's convenient. I often just ask for the CYA test though, as the rest is either static (like the phosphate level) or is easily checked at home (like the pH and FC levels).
What I should do is buy the CYA acid test kit, and perhaps another kit that has better granularity for the chlorine level, especially when it's higher than about 10 ppm FC.
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In belched:

Sometimes I do, but most times I don't. This past winter, I just left the solar cover on which kept a majority of debris out of the pool. I added remover about once a month and ran the pump on my usual schedule, except when it was freezing. I'm dealing with about a third of the volume you are dealing with, but before I learned about the phosphate removers, my pool would turn green , too. I then spend weeks clearing it up with alum and algae killers, but have used none of those since finding the phosphate removers

I have the same temps here in NTX through out the winter off and on, but it works for me. It does get cold most of the time, but I still haven't had an issue since using this method. Even if you can't find an industrial source, you have to way the cast of your time, water and scrubbing versus the cost of the retail cost. To me, it's not worth the hassle. After all, it's just money<g> and my time is worth more than the remover YMMV

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In belched:

Since using the removers I just look at the water. If it's clear and looks good, I don't worry about it. i may over use the removers, but it's cheaper than chlorine and most other chemicals
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ChairMan wrote, on Tue, 01 Jul 2014 20:53:22 -0500:

I understand.
There are two completely different schools of thought on phosphates: 1. Remove organophosphates, and the algae can't grow, plus add FC ... or 2. Maintain only a good FC-to-CYA ratio so the algae can't grow anyway.
Most people, I think, use both methods; but that second school of thought, mostly ascribed to by the FC-to-CYA ratio proponents, argues you have to have FC anyway, so if you maintain the FC-to-CYA ratio (of about 7.5% to 10%) then you don't need to worry about organophosphates. Plus, the phosphate removers don't remove organic phosphates; they only remove inorganic phosphates, both of which algae can use to survive (albeit more slowly on organic phosphates than inorganic).
Since I don't use chlorine over the winter anyway, I might try your rare-earth metallic salt experiment this winter.
Since I have time, I'd likely look for a dirt-cheap source of industrial rare-earth salt inorganic phosphate flocculators (chlorides or sulfates) than the pool-store Orenda PR-10000 (LaCL3, plus HCl to prevent precipitation in the bottle) or PhosFree Lanthanum Carbonate (La2(CO3)3, which also contains a clarifier to reduce clouding in the pool).
About 100 grams of industrial rare-earth salts would work since, apparently, there are 977 grams of lanthanum chloride (LaCl3) in one quart of Orenda PR-10000 phosphate remover (plus enough HCl to keep insoluble lanthanum hydroxide from forming in the solution at higher pH values).
The math works out to the following: a) 1 gram of LaCl3 flocculates 10 ppb phosphates in 10,000 gallons; b) So, 80 grams of LaCl3 removes 200 ppb phosphates in 40,000 gallons.
In summary, I have plenty of time to source an industrial non-reagent grade rare-earth salt so that I can run the experiment in the winter, and, if I find a good source, everyone else can get a price break on their phosphate removal tool also!
Note: Removing nitrates would also work, but usually that's more expensive than removing phosphates, so, I didn't explore that further.
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ChairMan wrote, on Tue, 01 Jul 2014 20:55:28 -0500:

The Orenda PR-10000 contains lanthanum chloride, LaCL3, plus acid (to prevent insoluble lanthanum hydroxide from forming in the bottle), and it's better than the PhosFree by most accounts (on the pool forums).
The PhosFree contains lanthanum carbonate, La2(CO3)3, plus a clarifier to reduce clouding in the pool, so, it works also (just not as well).
The local Leslie's doesn't carry the Orenda product, but it does have PhosFree at ~$50/2 liters (taxed) so that's roughly about ~$25/liter: http://www.lesliespool.com/natural-chemistry-pool-perfect-plus-phosfree-phosphate-remover/pool-perfect-plus-phosfree.htm
The better Orenda seems hard to come by, as it's unavailable at Amazon: (Amazon.com product link shortened)
And, it can't be shipped out of Texas: http://www.betterpoolsdelivery.com/orenda-pr-10000-phosphate-remover-1-qt/
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Oren wrote, on Wed, 02 Jul 2014 07:21:55 -0700:

Hi Oren, Thanks for looking up the sources of the Orenda PR-10000. It's amazingly hard to get shipped to California. I don't know why.
It's not cheap though, as that stuff is $100/gallon.
Seems to me we can find a bulk supplier of crude lanthanum chloride somewhere out there on the net for a lot less.
I had calculated 80 grams of LaCl3 removes 200 ppb phosphates in 40,000 gallons, so a mere 100 grams would set all of us free of inorganic phosphates I would think (depending on initial level).
The reagent grade lanthanum chloride is expensive too, at $1.50 to $2 per gram at Fisher Scientific (depending on size): http://www.fishersci.com/ecomm/servlet/fsproductdetail_10652_6420036__-1_0
Same at Sigma-Aldrich: http://www.sigmaaldrich.com/catalog/product/sial/262072?lang=en&region=US
But, for a pool, we don't need reagent grade lanthanum chloride. We just need the cheap stuff.
If we can find it.
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replying to DannyD. , chem geek wrote: I just saw this thread today and know that I'm posting late, but feel it's important to clear up some misconceptions.
*Don't Believe Everything You Read* First of all, you should not blindly believe what you read on the Internet from so-called "experts" and that includes me. Anyone can write anything they want and those with a financial interest or those with historical biases or those that don't understand chemistry (and some that do) can simply be wrong. This is why I try and link to multiple peer-reviewed papers in respected scientific journals and detail any original work so that others can follow it and assess it. I don't work in the pool/spa industry; I am just a homeowner with a swimming pool.
*History of Finding the Chlorine / CYA Relationship* The chlorine/CYA relationship was definitively determined in 1974 when the equilibrium constants for the multiple chemical reactions were accurately measured as described in the following paper presented at a water conference and published in a book that is out-of-print:
http://richardfalk.home.comcast.net/~richardfalk/pool/OBrien.htm
Applying these chemical principles to swimming pools started when Ben Powell created the Internet sites PoolSolutions and The PoolForum back in 1997 and determined through observation that in order to prevent algae in swimming pools that the FC level had to be raised when the CYA level was higher. He had some chemistry basis for understanding this FC/CYA relationship from some work by the chemist John Wotjtowicz who wrote papers in the Journal of the Swimming Pool and Spa Industry (JSPSI) starting in 1995:
http://jspsi.poolhelp.com
but though such papers were reviewed by some, this isn't a large standard scientific journal. Nevertheless, some significant and well-respected contributors to the pool/spa industry wrote papers in this Journal.
I joined The PoolForum in 2004 after I ran into cloudy water algae problems with my new pool using Trichlor tabs for 1-1/2 seasons even though I was using algaecide (though only every other week) and other products. My CYA had climbed from 30 to 150 ppm and that was with a relatively low 0.7 ppm FC per day chlorine usage due to the mostly opaque electric safety cover. That's when I decided to learn pool water chemistry to figure this out. I had majored in Physics and Chemistry at Cal Berkeley 25 years earlier (my LinkedIn profile is here: https://www.linkedin.com/pub/richard-falk/0/735/b25 ) and I delved in deep seeking out the core science including the out-of-print book that had the O'Brien paper.
Ben went AWOL from The PoolForum sometime in 2006 and that prevented new registrations to that site (that had grown to around 20,000 members) so some of the members formed some new sites in 2007 one of which survived and grew to be much larger, Trouble Free Pool (TFP) (http://www.troublefreepool.com ). The site now has over 75,000 members and gets over half a million visitors per month during peak summer (May, June, July).
In parallel with the above, Bob Lowry wrote two volumes of "Basic Training Manual" for the Independent Pool & Spa Service Association (IPSSA) and later wrote "Pool Chlorination Facts" where he described having a CYA level that was preferably 8-10 times the FC level though the context was having enough CYA to protect chlorine from sunlight and there was no discussion about a minimum FC/CYA ratio being needed to prevent algae growth. Later, Bob wrote "Cyanuric Acid: It Controls Your Pool" that at least in part took from many posts I had written and referred to the 7.5% FC/CYA ratio (I reviewed that article for Bob, but there was no attribution to my posts).
*The Chlorine / CYA Relationship* A decent summary chlorine and CYA with links to scientific papers may be found in the "Chlorine/CYA Relationship" section in the first post of the thread "Certified Pool Operator (CPO) training -- What is not taught" that also has other sections with other myths or misconceptions in the pool/spa industry:
http://www.troublefreepool.com/threads/17723-Certified-Pool-Operator -(CPO)-training-What-is-not-taught
The bottom line is that for saltwater chlorine generator (SWG) pools a minimum FC/CYA ratio of 5% is required to prevent green and black algae growth regardless of algae nutrient (phosphate, nitrate) level. For non-SWG pools, the minimum is 7.5%. Note that one can have a lower FC/CYA level if algae is killed or inhibited by other means such as by use of algaecides (Polyquat 60, linear quats, copper ions) or phosphate removers or if one is lucky to have a pool poor in algae nutrients. Yellow/mustard algae takes higher FC/CYA ratios to prevent (roughly 15%) so is better handled via complete eradication (when possible). One can also use products that work around CYA such as ammonia-based products that produce monochloramine that does not bind to CYA or sodium bromide products that essentially turn the pool into a bromine pool for a while (depending on dosage). There are pros and cons with each method that I won't get into here but are described in detail at TFP.
*Chemists Should Validate* Since there are some chemists who posted in this thread, they should validate the chemistry that is described and please suggest corrections to any mistakes they see (if any). Other chemists visiting the forums have made such reviews, but I'd always like more people to do so. The pool and spa industry is notorious for just making stuff up based on supposed experience (that often turns out to be inconsistent) instead of on the chemistry. Even the chemistry is not always looked at correctly.
For many years, the pool industry incorrectly interpreted the 10x rule for chlorine oxidation of ammonia by applying it to Combined Chlorine (CC). This was wrong for two reasons. First was that CC is measured in the same units as Free Chlorine (CC) namely as ppm Cl2 so molecular chlorine with a weight of 70.906 g/mole and this is NOT the same as ammonia which is measured as ppm Nitrogen (N) with a weight of 14.0067 g/mole, a factor of 5 difference. Second, CC already has one of the chlorine attached to it. So instead of the stoichiometry of chlorine to ammonia being 7.6 which was rounded up to 10 due to side reactions, chlorine oxidation of monochloramine has a stoichiometry of 0.5 so perhaps one could round to 1. Even for chlorine oxidation of urea the stoichiometry would be 3:1 chlorine to urea so perhaps 4x in practice. Finally, it's not as if anything gets stuck if you don't add enough -- you can just keep adding more chlorine to oxidize and in the case of urea it's slow anyway. So the entire "shock to 10x the CC level to get rid of it rule" was wrong and regular shocking should not be needed anyway if one is properly maintaining a sufficient FC/CYA level.
Though those who understand chemistry should really go through the CPO thread and its links to other threads and papers, the high-level concept of the FC/CYA ratio is basic chemistry. Though there are 13 equilibrium equations of the chlorinated isocyanurates, cyanuric acid, and hypochlorous acid (10 of these 13 are independent equations), the most important one that dominates the others at pool pH and normal pool chlorine concentrations (i.e. FC and CYA levels) is the following where "CY" denotes the core triazine ring (i.e. CYA) without the hydrogen attached:
HClCY- + H2O <<<----> HOCl + H2CY- "Chlorine bound to CYA" + Water <<<---> Hypochlorous Acid (chlorine) + Cyanurate Ion (variant of CYA)
The equilibrium constant for this reaction is a pK of 5.62 so 2.4x10^(-6) so with CYA levels typically at 30 ppm (2.32x10^(-4) M) and an FC of 3 ppm (4.23x10^(-5) M) the reaction is mostly towards the left as I show above with the arrows. At 3 ppm FC with 30 ppm CYA, 97% of the chlorine is bound to CYA and essentially inactive. Nevertheless, it is released quickly as the HOCl is consumed where half the chlorine bound to CYA can get released in 1/4 second. Of course, actual disinfection and oxidation rates depend on the instantaneous concentration of HOCl (and to a lesser extent to OCl- though this has substantially lower disinfection capability and only participates significantly in a few oxidation reactions). Fortunately, it takes a very low level of chlorine to kill pathogens and prevent algae growth. The 7.5% FC/CYA ratio corresponds to the equivalent active chlorine found with 0.06 ppm FC with no CYA at pH 7.5 and 77ºF temperature. Note that the above equation implies that CYA is in effect a hypochlorous acid buffer.
*Addressing Specific Comments in This Thread*

the chlorine / CYA relationship. Also, the chlorinated isocyanurate (e.g. Trichlor and Dichlor) manufacturers have long claimed that "CYA doesn't matter; only FC matters" which is simply not true. There were pool studies made to try and prove that CYA didn't matter, but because they looked primarily at uncontrolled bacterial growth through water samples in commercial/public pools and didn't look at kill times to prevent person-to-person transmission of disease, they could "prove" that bacterial growth was controlled by FC. However, they never looked at actual hypochlorous acid (HOCl) concentration (as I did). When one looks at that, one could just as easily draw the conclusion that it is what mattered. The data is not sufficient to distinguish well between them since bacteria are so easy to kill with very low active chlorine levels. Algae should have been easier to distinguish, but the study again did not give clarity there though the industry drew conclusions -- only 5 out of 486 pools had green algae even when there was zero chlorine, for example. With high bather loads, the ammonia from sweat and urine would quickly form monochloramine that could inhibit green algae, but the study also did not track use of supplemental algaecides. This study is described in more detail in the following thread:
http://www.poolforum.com/pf2/showthread.php/6649-Pinellas-County-FL-Pool-Study-1992 -(1994)

level is higher, then a proportionally higher FC level will produce the same active chlorine (hypochlorous acid) level so the same level of disinfection and oxidation since the chlorine bound to CYA has negligible such capabilities.

sunlight, higher CYA levels absolutely lower chlorine loss from sunlight. This is seen in thousands of pools where 20 ppm would simply be too low. Remember that Kent Williams of the PPOA is mostly writing for an audience of commercial/public pools and in that situation most chlorine usage/consumption is from high bather-load so only some CYA is needed to significantly reduce losses from sunlight and having it be higher isn't a lot of value (relatively speaking). However, in residential pools which are typically low bather-load, most chlorine loss is from sunlight so the higher CYA level reduces this loss.
What is most interesting is that this fact appears to be true even when one keeps the same FC/CYA ratio constant so has the same amount of unbound chlorine that can break down from sunlight. Apparently, the higher CYA level has some additional protective effect, perhaps where the CYA or chlorine bound to CYA helps to "shield" lower depths by absorbing UV, though we have not found specific scientific measurements (i.e. UV absorption spectrum) to support this, but detailed UV spectrum have only been done below the sunlight UV range of 300-380 nm so this is still an open item to be figured out (so we are going by observed results and a hypothesis).

came from a manufacturer of ORP sensors that Kent sold. It is inconsistent with known science as well as with subsequent observations. It's not just that ORP data is very unreliable and noisy both between sensors and over time, but that the graph is simply wrong when one takes real-world data from sensors. Actual data taken from 620 samples from 194 pools and spas that I showed in the post others linked to in this thread shows that ORP most closely corresponds to the hypochlorous acid (HOCl) level and that there is no maxing out at any CYA level as Kent's graph implied where all ORP converges at 70 ppm CYA. That simply is NOT true, at least not for today's ORP sensors. Perhaps the early Strantrol sensors had a problem of getting CYA interfering with the membrane to the sensors such that at a certain CYA level the data converged, but that does NOT mean that the active chlorine level all becomes the same at the CYA level regardless of FC level. The chemistry says that isn't true and every other peer-reviewed paper study plus real-world studies show that this convergence at 70 ppm to NOT be true.

PoolForum and Trouble Free Pool (and it didn't work for me). Many pools are naturally poor in algae nutrients so the lower FC/CYA ratios are not a problem since the algae grow more slowly so lower active chlorine levels can still kill the algae faster to prevent such growth. This is a classic example of where one projects one's personal experience to imply something about the chemistry/biology of what is actually going on, but this is inappropriate. By properly understanding WHY some pools get algae and others don't one can then control the variables that cause this distinction. My pool was very "reactive" to algae growth because I used metal sequestrants that were phosphate based (i.e. HEDP) and I had 3000+ ppb in my pool as a result (my fill water has 400 ppb phosphates, but with the pool cover I had very little evaporation and refill). So in spite of my using algaecide every other week, I got algae with 3 ppm FC and 150 ppm CYA. Had I used algaecide weekly, I could have gone longer. Without algaecide, the algae would likely have grown at around 50 ppm CYA or so if the FC were still held constant at 3 ppm. We see this over and over again on the pool forums.

(and biology) are clear. The ratio is real and the level of disinfection and algae prevention is related to that FC/CYA ratio, but since it is also related to the level of algae nutrients many pools will not get algae until that ratio gets much lower. Nevertheless, pools at or above that ratio will not get algae growth at least with a failure rate of less than 1 in 5000 pools. There are also issues with poor circulation in some pools, especially smaller above ground pools with one return and one skimmer so typically have terrible bottom circulation so pointing returns properly and regular (usually weekly) brushing are also required.
Note also that some pools don't build up CYA that much because the swim seasons are short, the pools are closed over the winter so are partially drained, some pools get summer or winter rain overflow for water dilution, some pools have sand or other filters that are backwashed for further water dilution, and some pools have total CYA loss over the winter possibly from bacteria conversion to ammonia (huge chlorine demand upon opening) or nitrogen gas or nitrate (no huge chlorine demand).

getting algae in their pools using Trichlor tabs and the recommended 1-3 ppm FC levels. It works for some because they have low algae nutrient levels or they don't have the CYA climb that high or they use supplemental products the pool store recommends including algaecides and phosphate removers as well as clarifiers, flocculants, enzymes and weekly shocking with "shock" products. Such supplemental products are much higher margin than chlorine, especially for the manufacturers.
Pool services are also keenly aware that they cannot simply use Trichlor pucks and maintain only 1-3 ppm FC. The pool store where I buy my 12.5% chlorinating liquid has a pool service out of two locations servicing 2000 pools and they use Trichlor but target 4.5 ppm FC. When the CYA gets to 100 ppm they usually do partial drain/refill of the water or if pools start to show higher chorine demand from algae growth they shock them with chlorinating liquid and if that doesn't work then they use a phosphate remover. Other pool services use copper-based algaecides though that risks staining in plaster pools and greenish hair for blonds. Some pool services in hot areas such as Arizona don't use Trichlor tabs, but use high CYA levels 100 ppm or so and add chlorinating liquid and/or chlorine gas to get to 14 ppm FC which then drops to around 4 ppm FC at the end of the week when they visit again. There are many ways to handle this, but they all are consistent with the chemistry.

but rather that the CYA chemical itself has chlorine attached to it replacing hydrogen. Look at Cyanuric Acid and compare it to Trichlor below:
http://en.wikipedia.org/wiki/Cyanuric_acid#mediaviewer/File:Cyanuric_acid.png
http://en.wikipedia.org/wiki/Trichloroisocyanuric_acid#mediaviewer/File:Trichloorisocyanuurzuur.png
There are some Cal-Hypo tablets, but they need special feeders and tend to fall apart as they dissolve and leave binder material. And, of course, they increase Calcium Hardness (CH). It's the chemistry that limits the choices of chlorine products. Sodium hypochlorite is unstable as a solid and even in water as a liquid is limited in concentration in chlorinating liquid to around no more than 15% (usually 12.5%). The only chlorine source that doesn't increase CYA or CH that is in solid form is lithium hypochlorite, but it is very expensive. Believe me, if it were possible chemically to produce a slowly dissolving tablet of chlorine without side effects, it would have been done, but it's not possible chemically (at least as far as anyone knows).

chlorinating liquid or bleach maintaining an FC/CYA ratio compared to using Trichlor. For my 16,000 gallon pool the chlorinating liquid and small amount of acid cost around $15 per month, but I have a pool cover that has my daily chlorine use be 1 ppm FC per day with the pool used for about an hour every day. More typical pools without covers would lose around twice that or 2 ppm FC per day at the 7.5% FC/CYA ratio. For Trichlor, you need to also add the cost of pH adjustment since Trichlor is net acidic and if you do that you find that the cost may be more than using chlorinating liquid or bleach unless one maintains a low FC/CYA ratio. In that case, one has to either be lucky with a pool poor in algae nutrients or one has to use supplemental algaecides or phosphate removers at extra cost.
Also note that the use of hypochlorite sources of chlorine including chlorinating liquid and bleach is close to net pH neutral. This is another one of those half-truths the industry makes where they simply don't understand the chemistry. They say that because the pH of hypochlorite is high that the pH will rise a lot in pools using such products and that this will require a lot of acid. What they apparently don't understand or certainly are not disclosing is that chlorine usage/consumption is an acidic process that exactly counteracts the pH rise from hypochlorite addition. The only net pH rise is from the excess lye that is added for stability and that is a fairly low amount. Most pH rise in pools using hypochlorite sources of chlorine comes from carbon dioxide outgassing and that can be mitigated through targeting a lower TA and higher pH, again based on the fundamentals of chemistry.

"standards" inconsistent with known chemistry and actual results in real pools. That may start to change with the Conference for the Model Aquatic Health Code (CMAHC) that for the first time in history will begin to look at the chlorine/CYA relationship via the actual equilibrium chemistry that has been known since at least 1974.

You solved it by using phosphate removers to remove one of the nutrients critical to algae growth. Because of that, you can operate at far lower FC/CYA ratios without having algae grow faster than the chlorine can kill it so in effect you don't need to worry about CYA, at least for algae growth. However, if your pool gets more bather load, you may find that it isn't as clear since the low active chorine level more slowly oxidizes bather waste, but in residential pools with low bather load this usually isn't a problem.
Remember that having the minimum FC/CYA ratio to prevent algae growth is an approach that works regardless of algae nutrient level. It lets one not have to use phosphate removers, algaecides, clarifiers, flocculants, enzymes, weekly shocking or anything other than chlorinating liquid or bleach and a small amount of acid. It is not the only approach. You can certainly use a phosphate remover and then not worry about the CYA level from the Trichlor tabs, at least as far as algae is concerned. In smaller pools or those with higher bather loads, the water can get dull from the bather waste not being oxidized quickly enough due to the lower active chlorine level from the lower FC/CYA ratio.
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On Sunday, September 14, 2014 7:44:01 PM UTC-4, chem geek wrote:

Trader4 here. You replied to Danny's post, but your comments are directed to what I posted, not Danny.
I didn't say it will work for everyone. I said that for most people, apparently following the guidelines set by health departments works, ie maintaining chlorine between 1 and 3 with CYA somewhere in the range of 25 to 75 or so. It works for me. It works for the several other people I know who have pools. I bet if you did a survey only a small portion of pool owners around here would even know what their CYA levels are. I think in practice, you find out what works for you, using some rational trial and error. All I was suggesting to Danny was that chasing high chlorine levels of 8PPM on the belief that he needs it because he saw it on the web somewhere doesn't make sense to me. And as I recall, he was doing it while using Trichlor, which is indeed a tiger chasing it's tail. IDK of any public health dept that recommends chlorine levels of 8, or even 5, do you?
I do agree that there is wide disagreement on the basic chemistry, what's going on. IDK that yours is right either, for example that shocking at only 4x combined chlorine is adequate as opposed to the more common 10x. Has anyone done any studies of actual pools, versus paper equations? That's what's important to me, what works.
And if the standards are wrong, one would think that the pool industry would get them changed. They own the industry and if they are wrong, just because they were written decades ago doesn't mean they should be cast in concrete.
By properly understanding WHY some pools get algae

There's an example of going outside guidlines. No one I know recommends 150 CYA. The max permitted by health dept guidelines, AFAIK, is 100. And that level isn't desirable, because of the inhibiting effect on the chlorine effectiveness. 25 to 50 is ideal. So, sure if you whack it out by 3X I would not be surprised to have problems.
Had I used algaecide weekly, I could have gone longer. Without

I think you're assuming that people who show up at some pool forum are a representative sample of all pool owners. I'd suggest that people with pool problems are an order of magnitude more likely to show up at a pool forum than those with pools without problems. If you made assumptions on leaking toilets based on postings in AHR, you'd conclude that the vast majority of toilets leak.

Well, then they're wrong. I have a pool here to prove it. Maybe it doesn't work for you. It works for me. And I don't know anyone that is targeting 8 PPM chlorine either.
The pool store where I buy my 12.5%

4.5 isn't Danny's 8
Other pool services use copper-based algaecides though that

And what happens the day of the service, the day after? People go in the pool when it's at 14? Health dept there OK with that?
There are many ways to handle this, but

OK, so what you're saying is that CYA isn't just added to trichlor tabs, it's an inherent part of the product itself. I didn't know that.

Well for one thing, Trichlor is the cheapest source of chlorine here. It's a cheaper cost of chlorine than the liquid chlorine at the supermarket or pool store. Danny went through the math too and came to the same conclusion. And trichlor is also a lot easier.
But the cost to maintain comment was to Danny who is keeping his chlorine at some high level, up to 8 PPM I believe. If he's doing that when 2 PPM could work, he's wasting money without regard to the form of the chlorine.
For my 16,000 gallon pool the chlorinating liquid and

Again, your experience is very different than mine. I've been using Trichlor since mid May. I tested the water back then, and the total alkalinity was low. I raised it with baking soda and since I didn't have enough baking soda and it needed to be raised more, I added sodium carbonate. Afte that, all I've done is add baking soda to raise the alkalinity and PH when needed. And I don't see the PH dropping from trichlor at all. It may drop a little, but not noticeably. PH drops noticeably after a heavy rain, because of the acid rain or if I have to add water. The well water is acidic. In either case, I then add baking soda to correct it. If it doesn't rain and I don't need to add water for 2 weeks, the PH stays the same. For the whole season I've gone through two bags of baking soda, $6 a bag at Costco. And that is for a 48000 gallong pool.
In that case, one has to either be lucky with a pool poor in algae

I haven't added any algaecide. And as I said, the folks I know who also have pools don't seem to be having any problems either. They start the pool up, use trichlor, keep the chlorine at 2-4ppm, shock occasionally.

I don't know what the definition of "a lot" is, but it does raise the PH significantly. I've used liquid chlorine and that is exactly what happens. It significantly raises PH. I have to then add acid to rebalance the PH.
What they apparently

The chemical process doesn't matter. The fact that you have to add acid to balance it out is what counts. And I'd much prefer to use 6 small trichlor tabs that I put in a feeder once a week, than run around with gallons of chlorine and acid every couple of days.

It's not inconsistent with my pool.
That may start to change with the Conference for the Model Aquatic

You're mixed up here. You've been responding to my points. The above statement was made by Danny. Danny is the guy targeting high chlorine levels, not me. I've consistently said that I maintain around 1 - 3 PPM and I don't have problems. Maybe once or twice a season I'll see some small amount of green algae start to form, then I shock it.
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replying to trader_4 , chem geek wrote:

high and one would then use a high FC to keep the FC/CYA ratio constant. At 50 ppm CYA the minimum FC to prevent green and black algae regardless of algae nutrient level is 3.8 so say 4 ppm FC. At 80 ppm CYA it is 6 ppm FC. So if Danny were already at 100 ppm CYA, it would have been better for him to lower the CYA level instead and then avoid stabilized chlorine products (Trichlor, Dichlor) to prevent a buildup of CYA.

be 4x, that is not saying one should shock to that level and I wrote that the oxidation is continuous and doesn't get "stuck". In other words, one doesn't need to shock at all and in a residential pool one can normally avoid Combined Chlorine (CC) by just maintaining the proper FC/CYA ratio. I use a FAS-DPD chlorine test that is part of the Taylor K-2006 and TFTestkits TF-100 kits and measure <= 0.2 ppm CC all the time and this is true for the thousands of others maintaining their pools the same way.

assume that FC and CYA are two separate parameters that are not related so that a high CYA level inhibits chlorine regardless of FC level while a low one does not, but that is not at all how it works (did you read the info on chemical equilibrium that I wrote?). The amount of active chlorine (hypochlorous acid) that does the disinfection of pathogens, killing of algae, and oxidation of bather waste is proportional to the FC/CYA ratio. That's a chemical fact not only determined explicitly by the equilibrium constants but also proven in practice in kill times, oxidation rates, and indirect measurements (ORP) by the peer-reviewed papers in respected scientific journals -- 5 of them on bacteria, 2 on viruses, 3 on protozoan oocysts, 1 on oxidation, and 2 on ORP. I linked to all of these in the CPO thread I linked to in my post.
In terms of active chlorine level, 3 ppm FC with 30 ppm CYA is identical to 6 ppm FC with 60 ppm CYA is identical to 10 ppm FC with 100 ppm CYA is identical to 20 ppm FC with 200 ppm CYA. These all have the same hypochlorous acid concentration and the same disinfection and oxidation capability (well, the highest ones become more significant due to the chlorine bound to CYA having a small oxidation effect which is no more than 1/150th the rate of unbound chlorine).
Also, there are quite a few pools with more than 100 ppm CYA and they get reported a lot. If the daily FC usage rate is 2 ppm per day, then that's an increase in CYA of 36 ppm per month. This is the typical loss rate if one maintains an FC/CYA level to prevent algae growth regardless of nutrient level. If a pool is low in phosphates, then one might be down at half that, say if your FC/CYA ratio is around 4% so 3 ppm FC with 75 ppm CYA or 1 ppm FC with 25 ppm CYA. So that would be a CYA increase of 18 ppm per month. If you have water dilution from summer rain overflow, backwashing sand filters, and carry-out, then one can keep their CYA in check and not get over 100, especially if they have additional partial drain/refill or winter rain overflow from closing. However, not every pool is like that. Oversized cartridge filters may only need to be cleaned once a season and in some areas pools get no summer rains and over the winter are not closed and may be covered which prevents dilution. My pool went from 30 ppm to 150 ppm over 1-1/2 swim seasons and I never had the FC above 3 ppm and had only 0.7 ppm FC per day chlorine usage.
Also, some people shock with Dichlor where the CYA builds up even faster. Not everyone maintains the pool as well as you have with regard to preventing CYA buildup. And most certainly not everyone has avoided phosphates the way you have.
I am not saying that one could not use a phosphate remover to then not worry so much about the FC/CYA ratio, but at a lower FC/CYA ratio you do have lower rates of disinfection and oxidation. For residential pools, this isn't a big deal unless the rate gets very low or bather loads get higher, mostly affecting water clarity. I've seen less than a handful of cases out of the thousands of reports of people getting infections from residential swimming pools, but there have been many more seen in spas and some of these were from Dichlor-only users that had significant CYA buildup (others were from use of "alternative" systems while others were from not using enough chlorine to oxidize bather waste so letting it get to zero).

of stabilized chlorine products. Some come for other questions regarding pool builds, new pumps or solar systems, equipment repair, converting to a saltwater chlorine generator, etc. Nevertheless, the number of people with algae problems is astounding and the number of reports of people going to pool stores with algae problems is also large. I don't claim it's even the majority of pools, but with 10 million pools in the U.S. it's still a significant number that I'd estimate to be somewhere around 20% in any given year. And you can't assume that everyone having a problem with their pool will come to a forum either -- the vast majority go to their pool stores instead and get sold shock, algaecide, phosphate removers, clarifiers, flocculants, enzymes, etc. So it cuts both ways even if the sample were biased.
As I wrote, pools can be naturally poor in algae nutrients, particularly in phosphates. If you don't have phosphates in your fill water (it's added by some municipalities for corrosion control) and don't use HEDP-based metal sequestrants and don't get blown-in fertilizer, then your phosphate levels may remain low. Also, with significant water dilution your CYA may be kept in check.

state, but as shown in the following link:
https://www.flrules.org/gateway/readFile.asp?sid=0&tid=0&cnodE-9&caid@8872&type=4&filedE-9.doc
Florida allows up to 10 ppm FC and the following link:
http://info.sos.state.tx.us/fids/25_0265_0204-4.html
shows Texas allows up to 8 ppm FC and the following link:
http://www.health.state.ny.us/regulations/nycrr/title_10/part_6/subpart_6-1.htm#s6111
shows New York allows up to 5 ppm FC (and New York does not allow CYA for commercial/public pools). These all exceed the 4 ppm FC maximum from the EPA that is based on drinking water limits and is the most you will see on any label of a chlorine product:
http://water.epa.gov/drink/contaminants/
The reason Florida and Texas have such high FC limits is that they are hot sunny environments so use CYA outdoors to help prevent chlorine breakdown from the UV in sunlight. However, they realize that with the higher CYA levels the lower FC of 1-3 or even 4 ppm allowed by the EPA simply doesn't work since it doesn't oxidize fast enough nor prevent algae growth. Nevertheless, their code does not specify an FC/CYA ratio but still has separate FC and CYA ranges and that is inconsistent with the science of what really goes on and is what may get changed with the CMAHC.
As far as the 14 ppm FC, again you don't seem to understand the relationship of chlorine and CYA because you think of 14 as a high number so it must be bad while you are completely ignoring what happens when CYA is in the water. The 14 ppm FC with 100 ppm CYA has the same amount of active chlorine (hypochlorous acid) as 0.13 ppm FC with no CYA at 77ºF (0.29 ppm FC with no CYA at 88ºF). This is far, far less active chlorine than found in pools not using CYA such as many indoor commercial/public pools. The people using the pool at such high FC levels do not experience any problems with it -- no stinging eyes, no unusual effects on skin or hair, etc.
In fact, my wife has personal experience with this difference since she used to use a local community center swimming pool during the 5-month winter season every year and her swimsuits would have to be replaced every season since the elasticity would get shot while in our own pool during the 7-month summer season her swimsuits would last for around 7 years. The indoor pool also resulted in much more noticeable effects on skin and hair compared to our pool. The difference is that the indoor pool used 1-2 ppm FC with no CYA while our pool used 3-6 ppm FC with 40 ppm CYA. Our pool had the equivalent of only 0.14 to 0.30 ppm FC with no CYA so a factor of 3 to 14 difference. This corresponds very well with the rate of destruction of the swimsuits.

for pH/TA adjustment. If your TA is higher, then the rate of pH rise from carbon dioxide outgassing can compensate for the pH drop from Trichlor, but the TA still drops. Now if you have evaporation and refill, then some TA can come from fill water especially if the TA level is high in such water (you have well water, so it may be higher in TA), but if I ignore that (evaporation is minimal in pools with pool covers, for example) then for every 10 ppm FC added by Trichlor it increases CYA by 6.1 ppm and decreases TA by 7.1 ppm. Every pound of Trichlor needs 17.35 ounces weight (just over a pound) of baking soda to restore TA, assuming the pH is getting balanced by carbon dioxide outgassing.
So in figuring Trichlor costs for most people, you have to add the cost of baking soda to the Trichlor. Using the following link for Trichlor pricing:
http://www.poolgeek.com/products/glb-large-3-inch-tablets-25-lb
that's $91.14 for 25 pounds so $3.65 per pound. I'll use the low baking soda price from Walmart:
http://www.walmart.com/ip/11027507?wmlspartner=wlpa&adid "222222227009139635&wl0=&wl1=g&wl2=c&wl3@343149832&wl4=&wl5=pla&wl6x303010592&veh=sem
which is $2.24 for 4 pounds so $0.56 per pound (if I used pool store chemicals, then it's $21.64 for 15 pounds so $1.44 per pound). So the net cost for one pound of Trichlor and 17.35 ounces weight of baking soda is $4.26 ($5.21 if pool store Alkalinity Up was used). One pound of Trichlor produces 11.0 ppm FC in 10,000 gallons which can be obtained with 112.3 fluid ounces of 12.5% chlorinating liquid. I get mine for just under $4 per gallon so this is $3.51. I also use a small amount of acid, but if I use 2 cups at $5 per gallon this is $0.62 for a total of $4.13. So this gets more comparable, but many people are able to find chlorinating liquid or bleach at lower prices than what I gave (I live in the S.F. Bay Area that's more expensive -- chlorine in southern California and in Florida is less expensive, for example).

remover then yes the operating cost would be lower using a lower FC/CYA ratio because the chlorine loss rate would be lower due to the lower active chlorine level and that lower operating cost should even make up for the pricing difference I noted above. However, one must then factor in the cost of keeping the phosphate low. For you, that might be zero if your phosphates are naturally low, but for others that may not be the case. I have 400 ppb phosphates in my fill water, but my pool cover prevents evaporation and therefore refill, but others with uncovered pools and high phosphate fill water would need to regularly use a phosphate remover at extra cost. Also, you have a situation where your CYA is kept in check via some water dilution, but others are not in that situation with oversized cartridge filters and dry summers and no winter pool closing.

my pool nor does anyone else properly maintaining the FC/CYA ratio. There is no need and the pools not only don't get algae but they are crystal clear even with higher bather loads. Again, it's not the only approach -- it's just a different approach. If you want to use a low phosphate approach with a lower FC/CYA ratio, that's fine, but for those that get regular increases in phosphate levels and have higher CYA increases it may not be as practical nor economical.

small. The reason in YOUR pool that chlorinating liquid or bleach would raise the pH over time is that your TA is too high. TA is a source of rising pH because pools are over-carbonated and TA is a measure of that. The outgassing of carbon dioxide causes the pH to rise (with no change in TA). People using chlorinating liquid or bleach should maintain a lower TA and that reduces the amount of acid needed. Yes, when one adds a hypochlorite source of chlorine the pH rises, but then it drops back down when the chlorine is used/consumed. The only net pH rise is a very small one from the excess lye and a larger one from the carbon dioxide outgassing, but the latter can be minimized by having a lower TA. Again in YOUR situation, if your fill water is high in TA and you have evaporation and refill, then you've got a "free" source for at least some of the TA, but that is not everyone's situation.
Now the convenience factor of having much less weight to carry is an important one, especially for your larger pool size. That's probably the most important reason where in your situation Trichlor works better for you. I'm not saying you should use a different method, but that you shouldn't project your own experience to others since their situations for water dilution, phosphate introduction, and fill water TA level may be different than yours.

least those with decent circulation as I had alluded to earlier). After I switched to maintaining the proper FC/CYA ratio, I no longer got any algae at all and never had to shock the pool and this was in spite of 3000+ ppb phosphates in the water. There are others with higher levels of 5000 and even one with 20,000+ ppb due to very heavy use of HEDP-based metal sequestrants due to blown-in iron from volcanic material in Hawaii, yet with the proper FC/CYA level algae is prevented without the use of additional products. Again, it's not the only way, but it is a method that works.
I think the bottom line, especially for your pool, is that your situation is better suited to using Trihclor for a variety of reasons. For others, including my own pool, that is not the case. What is important is that people understand their options and why one method may work more economically or conveniently than another for THEIR particular situation.
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