Safe swimming with elevated chlorine

[chem geek]

Ben and Carl,

Since some of the Disinfection By-Products (DBPs), including Trihalomehtanes (THMs), are known to be a problem with long-term exposure at levels of 0.08 ppm, the issue is not whether chlorine disinfection poses risk, but rather whether the risk is low relative to the risk of infection (Ben's point in earlier posts).

The rate of reaction for any chemical process is dependent on the concentration of each of the reactants as well as on temperature (and if catalysts are present, etc.). In a CYA pool, the concentration of the chlorine (HOCl and OCl-) that reacts with organics to produce DBPs is exceptionally low, typically around 0.1 ppm for HOCl and OCl- combined, so the rate of production of DBPs will be very low as well. In a non-CYA pool, as found in indoor pools, the level of chlorine (all of which is in the form of HOCl and OCl-) is usually at least 2 ppm, or 20 times higher. This higher level of chlorine is closer to the chlorine disinfection rates used in water treatment where the concern of DBPs (and the switch to using chloramines) has taken place (and remember that the concerns were with drinking the water, not just bathing in it). With the same organic loads, this means that the rate of production of DBPs will be 20 times higher. Spas have a higher temperature so 104 degrees vs. 80 degrees might have a higher rate of DBP production of 1.5x-4x (I couldn't find the rate constants and their temperature dependence for DBP production, but generally 10 degree Celsius higher temperature increases the rate by the range I indicated).

Ben had noted that asthmatics genearlly have problems only with indoor pools. I suspect that the lack of CYA use in indoor pools is at least part of the problem. Poor air circulation and the lack of sunlight which might breakdown the DBPs are other factors. This is part of the reason why I believe a small amount of CYA should be used for indoor pools though this would pose problems for easily shocking the pool (non-chlorine shock would probably need to be used).

My own personal experience (actually that of my wife's) is that the rubber in swimsuits breaks down rapidly (over one winter) when used in an indoor pool that I presume is not using CYA while there is no noticeable breakdown when used in our outdoor pool with CYA over the summer. Though rubber is not a typical organic from living things, it still gives credence to the principles outlined above. One of these days, I'm going to take my test kit down to the indoor pool my wife uses in the winter and will see what's really in that pool!

Richard (aka "chem geek")

[CarlD]

Richard:
the question that leaps to mind is what are the levels of CYA and FC that you are referring to and does this ".1" change as either or both CYA and FC change?

[CarlD]

Ben,
I have read your last post several times, and gave a reply that one time seemed to address it.

Now as I look again I see that you seem to be putting the context of the anti-chlorine people writing out there in the aether as being posters on your board.

The two forms of the argument need to be properly defined.

In running PoolForum you have set up a particular set of rules and standards that you expect members to adhere to. Fair enough--I don't pretend this is the public news media where all sides need to be presented.

Therefore I have NO objection to you preventing the anti-chlorine crowd from dumping their particular message here, nor do I object to your reasons--you see it as bad science and as dishonest propaganda. I don't disagree.

One of the reasons I have agreed to participate as a moderator is that, like you, I am tired of people being fed fairy tales (and EXPENSIVE ones too) about their pool care. I see PoolForum as a growing voice in the wilderness that, with demonstrable successes is showing how other techniques (for lack of a really good work for them) fail--consistently. I don't "believe" your techniques work--I don't have to take it on faith. I've observed them working repeatedly and predictably in my own pool and in the pools of others.

I don't feel you need to give "equal time" to people pushing the "slug" method of lowering T/A, to the electromagnets that show up, to the Nature2 type systems. When they show up with good science, I won't have to convince you to give them an airing--I know that you will simply review it and decide if the science is valid--no matter where it takes you. Till then, they go in the tinfoil hat cabinet or the Hall of Shame.

You're not bound to publish lies and liars.

But what happens when you are trying to change policy, and get involved with politics? You say you demand orthodoxy in your forum. Thankfully, I think that's not accurate. You always seem willing to investigate new ideas, and have them investigated, as long as there is a sound basis for doing that (not tin-foil hats here, please).

For example: When I first visited the PoolForum years ago, you were very skeptical about Intex donut pools--discounting the value and validity of them. You were fairly leery of A/G pools in general, though you have a section on them in PoolSolutions as well. And, of course, I had one of the early Intex EasySets. Still do, if the mice haven't eaten through it, buried somewhere in the shed. I argued: Wait a second, it's a real pool with real water, a real filter, you get just as wet--and the chemistry needs to be addressed. In fact, my favorite image is lying in a floating armchair, with a drink, on a lazy afternoon, listening to the ball game--and that it makes no difference if it's a donut or an inground.

Over the years I've seen you soften--even put forth the idea that AG pools get used MORE because people won't tolerate them in their yards if they are not using them--they'll get torn down faster than an IG will be abandoned.

Another example: DE in sand filters. Al and I have both been delighted with the results and have suggested other people try it, frequently. It's not orthodoxy, but it's logical. And you haven't said "No more discussion of DE in sand filters."

I could cite other examples, I can think of several--but all of them have something in common: they all had a logical basis and you "succumbed" to logic. To me, that's not orthodoxy. Unless, of course, your orthodoxy is facts and logic and truth, wherever it takes you.

But the other side is the side of politics and policy--the art of compromise. Sometimes you just have to hold your nose. Not here, not on the board, but out there when we go into our polling booths and form our coalitions to get something or other done. The "fellow travellers" in ANY political movement always have an unpleasant amount of mishegoss. A political movement is ANY organizing to influence the government--whether by convincing law makers to change laws, or electing law makers. There's always going to be people with that mishegoss.

I'm a motorcyclist, been one a lot longer than I've been a pool owner. There's ALWAYS someone posturing to limit or outlaw our activity. Frequently, it's in a way that's only good for one thing--drumming up votes. Even more frequently, they are citing BS put forth by the insurance industry (Bikes are very inconvenient to to them ) Sometimes, a lot of the OTHER positions of that person are ones that I agree with. I may HATE their position on bikes, but on other things that are far more important, the other candidate is worse. What do I do? Do I become a single issue voter, or do I do a cost-benefit analysis?

Then, of course, comes the great betrayal when the person gets elected and does the OPPOSITE of what they promised.

[chem geek]

Carl,

To keep my message short, I didn't give all of the details. With the following conditions:

pH: 7.5
FC: 3.0
CYA: 30
The following don't have a much smaller effect on HOCl:
Temp: 80ºF
TDS: 550
The following has no effect on HOCl:
CH: 300

You get 0.045 ppm HOCl and 0.048 ppm OCl for a total of 0.093 or about 0.1 ppm total for HOCl and OCl-.

I have been in communication with Ben on the detailed spreadsheet I created and plan to start a thread in the China Shop (perhaps this weekend) to start the discussion on getting real-world experiences from people. Though I am confident of the chemistry determining HOCl levels at various levels of CYA and FC and am also fairly confident of the 0.011 ppm HOCl level that is the minimum for disinfection (of easy bugs, not hard-to-kill ones), I am not at all sure what the proper levels of chlorine are needed to prevent algae nor to properly shock algae (and will likely vary by type of algae). This is where some real-world experience could help determine these values.

The spreadsheet is complicated and solves the chlorinated cyanurate equations iteratively since an exact solution requires solving a quartic equation (or ignoring a very minor species, a cubic equation) and even then you need to iterate to solve for the ionic strength influences on activity. Nevertheless, there is an approximate formula you can use so long as your CYA ppm is at least 5 times your FC (the formula really falls apart terribly below a ratio of CYA/FC of 3).

(ppm HOCl) = (ppm FC) / ( 2.7*(ppm CYA) - 6.6*(ppm FC) + 5.2 )

and if you are interested in the FC for a given HOCl (to construct the equivalent of Ben's table, for example), you can use the following which just solves for ppm FC from the above.

(ppm FC) = ( 2.7*(ppm CYA) + 5.2 ) / ( 6.6 + 1/(ppm HOCl) )

The constants in the above formulas are for a pH of 7.5 (which is the only parameter that significantly affects these constants). With the spreadsheet I can easily calculate the constants for other pH, but remember that the above formulas are approximate. For example, with FC of 3 and CYA of 15 the formula gives HOCl as 0.117 when the correct answer is 0.107. That's not bad (about a 10% error). However, with FC of 5 and CYA of 15 the formula gives HOCl as 0.400 while the correct answer is 0.246 (about a 60% error) which isn't very good.

Richard

[VOLDADDY]

Wow, the above post might as well have been written in Chinese to me, and I suspect 90% of the others here. We really appreciate all of the work people like Ben, Carl, Richard, Al, Janet, Michael and the bleach calc, et al...put in to this board, and breaking it down to laymans terms for everyone else to understand. Now I see why I didn't take chemistry in college, Biology and the 3 hour lab was enough for me. Kudos from everyone for all the work you guys and gals do. Too bad we all don't live near each other, or we could have a huge cook out and grill up some steaks to show our appreciation! (medium rare, of course )

[DavidD]

pH: 7.5
FC: 3.0
CYA: 30
The following don't have a much smaller effect on HOCl:
Temp: 80ºF
TDS: 550
The following has no effect on HOCl:
CH: 300

Richard,

What effect, though small, does TDS have on HOCl? Would the fact that salt makes up the majority of TDS in a particular sample increase the negative effect? Go easy on my limited abilty to grasp basic chemistry .

Dave

[chem geek]

Richard,

What effect, though small, does TDS have on HOCl? Would the fact that salt makes up the majority of TDS in a particular sample increase the negative effect? Go easy on my limited abilty to grasp basic chemistry .

Dave

In the presence of even small amounts of Cyanuric Acid (CYA), TDS has almost no effect on HOCl. So the calculations for a salt (SWG) pool would be the same as for a regular non-salt pool.

In a pool with no CYA, then the HOCl concentration from a non-salt pool to a salt (SWG) pool is lowered by around 5.7% (independent of Total Free Chlorine (FC) level).

Stop reading at this point. The following is for those who might want a more technical explanation.

(The technical reason for the difference is that without CYA, the TDS affects something called "ionic strength" that affects the equilibrium between the neutral HOCl and the charged OCl-. With CYA, the concentration of HOCl is instead determined by the CYA-like equilibrium that has charged species on both sides of the equation so the ionic strength effect is cancelled out. )

[fcfrey]

So ---- What have we learned??

After nearly two months, 90438 Characters (with spaces), making up 15683 Words, in 45 posts from 12 different contributors including our Administrator and Moderators, we have had a very spirited debate. We went over, under, around and some, directly to the question, which in case we have forgotten, “Is it safe to swim with an elevated chlorine level?”

1. We have explored the politics, the fears, the fear mongers in the “Greenie” gang, and the chemistry behind effective chlorination.

2. We’ve also discussed the way our mainstream media runs off with half of the story and creates the rest itself, true or not, to “sell papers”. Ben has very accurately pointed out the fact that “the fears that people bring to the Pool Forum are not, for the most part, irrational fears. Rather they are a rational response to the persistent and hyped anti-chlorine hysteria shrieked out by modern environmentalists and uncritically parroted by the mass media”. The latter being one of the most profound statements of the entire thread.

3. We have learned that there are many forms of disinfection available for our pools including sunlight, UV, peroxide, bromine etc. etc., but none do the job as effectively as chlorine.

4. We have learned that the real dangers are from the disinfection by products (DBPs) and Tri-Halo-Methanes (THM) particularly in indoor pool environments, but these problems really do not apply to our outdoor residential pools where there is plenty of ventilation. In addition the fear of chlorine being directly absorbed through the skin has been largely debunked, but there is evidence that some halogenated compounds -- that may, or may not be present in pools -- can be so absorbed. We should, however, keep in mind that these compounds are found in pools in many forms including salt and the very liners that keep the water where it belongs (in the pool).

5. We’ve discussed lighting and algae formation in aquariums and the relationships to disinfection and sanitation.

6. We even discussed DDT.

7. We have learned that there are some members of this forum that are overly sensitive to what other members quote and are willing to lash out with concealed retribution, leaving the recipients with their “feel bad” hurt.

8. We have learned that there is a need for compassion for the “unlearned” and those skeptical of the principles and practices taught here.

9. And finally, we have gone --- w-a—y off topic to explore the area under CarlD’s bed

But what about the question-----------------?????

I think it is safe to say, “that all depends”. It depends on who is doing the tests, and are they accurate. It depends on how high your cyanuric acid level is. It depends on the level of your chloramines (combined chlorine). It depends on every other chemical we put into the pool. It depends on the environment in which your pool exists. But it really depends on how comfortable you are with what the administrators, moderators and other contributors on this forum believe.

For me --- nearly two months after posting the question, and reading another 1000 or more posts on a lot of related subjects, I will now swim in my pool whenever it is 10 ppm free chlorine or less. I’m comfortable with that decision, a decision that I probably would not have been able to make without the debate that my question has brought forth.

I’ve added another 656 words to this thread so I need to bring it to a close.

Lastly --- I feel compelled to thank Ben, for providing this forum. Richard, for his detailed chemical explanations and charts. The Moderators who keep things going forward with their great advise. And finally all the newbies, some of whom ask some of the most ridiculous questions (sometimes they make me laugh) which bring out the very best information money could never buy.

Frank