Is a Pool Chlorine Level Above 10 PPM Unsafe?

[han78216]

Admin note: this is a copy of the first 4 posts of this thread:
http://www.poolforum.com/pf2/showthread.php?15974


Hello everyone. I recently moved to a new house with a pool and I have been reading up this forum and started using BBB method.

The pool, in-ground 25k gallon, water is pretty clear now, but I still get algae on the wall even though I keep chlorine level at above 5ppm all the time.

I recently got the testing kid everyone is recommending and found that CYA is somewhere between 240-300. I had to dilute the water twice. and ph level is 7.5.

Is having CYA@240 the cause of my algae problem? How much water should I replace in order to bring it down to the acceptable level? say 50?

[PoolDoc]

Yes. With CYA=240 ppm, you'd need a MINIMUM chlorine level of 12. If you leave it there, you'll need to dose to about 20-25 ppm 1x per week, and let it drop to 12 before redosing. With a little practice, you'd be able to work out 1x per week dosing.

CYA=240 is a perfectly acceptable level to ME, but not to all the moderators here. Current recommendations are about 50 ppm for general use; 80 ppm for SWCGs, and 150 ppm if you are frequently gone and need to set up 1x per week treatment.

With a 25K gallon pool and CYA=240ppm, you'd need to drain 190/240 x 25K gal, or 19,000 gallons in order to be at 50 ppm when you've refilled. That's what most folks here will tell you do do, and it's what I would have recommended, 2 years ago.

What I currently would recommend is this:
1. Switch to a non-stabilized form of chlorine -- bleach, cal hypo or SWCG (If you need help on sources, let me know)
2. Add borax to the 60 ppm level (24 boxes of 20 Mule Team borax + 7 gallons of muriatic acid)
3. Let your CYA drop over the next few years.
4. Add chlorine 1x per week.

Going that route will give you extremely stable chemistry at very low cost, and you'll only have to dose 1x per week. If you have a sand filter, and use cal hypo -- I'll need to give you special instructions -- you will end up with VERY clear water.

If you do NOT want to switch to a non-stabilized form of chlorine, I'd recommend draining the pool completely since your stabilizer will start to rise as soon as you start adding chlorine.

[han78216]

What's the acceptable level for he chlorine level? Does it depend on CYA level?
We have two young children. I didn't want to raise the chlorine level too high because of them.

Will 12ppm or higher be safe for people to swim in?

[PoolDoc]

Will 12ppm or higher be safe for people to swim in?

Yes. Not "perfectly safe", because nothing is "perfectly safe" -- but the primary risk to your children in the pool, by a VERY large margin, is overexposure to dihydrogen oxide, rather than overexposure to chlorine.

We'd been reluctant to say yes, for a number of years, even though many of us have swum in pools at 12 ppm or higher. But, this spring, in researching some claims of "chlorine allergies", I found that dermatologists have for years been recommending "bleach baths" at 50 - 100 ppm chlorine with NO stabilizer for patients, including pediatric patients, with eczema and other skin conditions.

Here's that data we have at present:

+ Bleach bath use at 50 - 100 ppm, as a dermatological treatment for both adult and pediatric patients. (Please note: these were naked bleach baths. 100 ppm of chlorine, in the absence of stabilizer, will do serious damage to most women's swimsuits!)

+ Pool Chlor of Arizona and other pool service companies have used chlorine gas to treat 10,000's of home pools since the 1960s in a process that involves stabilizer levels around 150 ppm and chlorine levels that are 15 - 20 ppm at the end of each weekly chlorine injection treatment, but fall to 5 - 10 ppm by the end of the weekly treatment interval.

+ Personal observation #1: In the late 1990's I was servicing a pool in the subdivision where US Congressman Zach Wamp was living. One of the pool staff made unauthorized changes to the feed system resulting in kiddie pool chlorine levels that had been falling, but were in excess of 100 ppm when I arrived, and found the problem. The feed system had been turned off, so levels would have been falling. My best estimate, from talking to the head guard and trying to determine what had happened, was that the changes had been made 3 days before, and corrected 24 hours later. The kiddie pool had been in HEAVY use during this entire period.

What was done was done, so I drained most of the pool into the main pool, and then refilled it, lowering chlorine and stabilizer levels to more typical values. I asked the head guard specifically, but she had had ZERO complaints, even though many infants had used the pool. We'd both seen how simply hearing about a problem would generate complaints ( I did this as an experiment on one pool, years ago, announcing a fictitious problem) and so we said nothing. But I asked to let me know immediately of any complaints that did arise. There were none.

+ Personal observation #2: Around 1998, the Chattanooga Warner Park 50m pool was being used by several USS teams for long course training. I knew a number of the elite swimmers, since many of them worked as guards I serviced, and because my son was a fairly elite younger swimmer at that time. During a one month interval, the pool had some 'control' issues, resulting in OTO 'orange' chlorine levels (20 - 50 ppm) (I wasn't servicing the pool so I couldn't check too closely). Stabilizer levels were very low during this period. The results of swimming in this pool with 20<FC<50 ppm and 0<CYA<20 ppm for 2-3 hours per day, 6 days per week were:
a. loss of all fine body hair
b. dry skin
c. destruction of multiple swimsuits (both guys and girls wore Lycra swim suits)
d. the guys who did NOT wear swim caps had ash-colored hair, with 'goggle-stripes' where the goggle straps protected the hair underneath, which retained it's original color.

+ Personal observation #3: Around 2000, my son was swimming at the McCallie School indoor pool, which experienced similar control problems. I did test this water, but only by dilution, since I did not have the DPD-FAS test at that time. Levels were 15<FC<30 ppm and CYA=0 ppm. This continued for 3 - 4 weeks, until I called the health department. My son, who had moderate to severe asthma, had had NO breathing problem beyond normal, did lose a suit, and did get the stiff, ash-colored hair, but experienced no other ill effects.

+ Analytical observation: Beginning around 2005 (I'll let him comment on this) Chem_Geek took earlier laboratory research and distilled it into an analytical spread sheet that allows calculation of actual HOCl, and -OCl levels, given DPD chlorine levels, pH and CYA levels. Over the past 8 years, both here and at TroubleFreePools, an increasing body of empirical evidence has validated his analytical conclusion that the EFFECTS of chlorine in water are primarily a function of the HOCl and -OCl components. Stabilized chlorine compounds in the water constitute an effective and instantaneously available chlorine RESERVE, but are not themselves active, until the HOCL levels are reduced, allowing the stabilized chlorine compounds to release their 'reserve'.

+ Bureaucratic observation: The US EPA regulates the treatment of potable water by public utilities. Until recently (maybe 12 years ago?) there was NO upper limit on chlorine levels in drinking water. Even today, the upper limit of 4 ppm FC is an ACTION limit. What this means is that the utility is not in trouble, does not have to report a violation to the EPA OR to its customers, but rather simply has to begin to take "ACTION" to lower the chlorine levels. The fact remains, public utilities ROUTINELY provide DRINKING water to some customers that is at or near FC=4ppm, and occasionally provides water at 10 ppm FC . . . and this has not caused any reported problems I am aware of.

+ Literature: I have collected over 8 Gigabytes of peer-reviewed articles on water treatment (and will be publicly indexing them at SwimmingPoolResearch.com, beginning this fall) and have no articles reporting ill health effects on swimmers as a result of chlorine levels that are 10ppm<FC<100ppm. (Those levels do trash hair and swimsuits, as noted above, in the absence of high CYA levels, though I don't have reports on that, either.)

This is probably more than you wanted -- but it's a question that's going to come up as a result of changes in what I'm suggesting. So I took the opportunity to answer your question somewhat more fully than you might have desired.

I'm going to put a copy of this thread in the China Shop here:

http://www.poolforum.com/pf2/showthread.php?16011so those that want to continue the technical "Is high chlorine bad for you?" discussion, can do so there, and leave this thread for your personal questions.

[chem geek]

The active chlorine level that oxidizes swimsuits, skin, hair, corrodes equipment, oxidizes bather waste, creates disinfection by-products, etc. is very low when there is CYA present because its amount is roughly half the FC/CYA ratio. So when we recommend something on the order of an FC that is 10% of the CYA then the active chlorine level is roughly equivalent to around 0.1 ppm FC with no CYA where about half of this is active chlorine. In other words, it's very low and therefore safe.

The ONLY issue with a high FC level on its own, independent of CYA level, is if you were to drink a lot of pool water since that is when this FC number matters because it represents the capacity/reserve of chlorine. It may not react very quickly because of the CYA, but in any given amount that you swallow, there will be a lot of chlorine, assuming the FC level is very high. So the question is how high is high? The EPA limits drinking water to 4 ppm, but that is for drinking 2 quarts of water every day for a lifetime. In practice, 10 ppm FC won't be a problem and since you aren't drinking the pool water even higher levels are not an issue.

So unless you expect your kids to be drinking lots of pool water, then it's safe even at 20 ppm FC assuming you have CYA in the water (even 20 ppm CYA or more would be enough to moderate chlorine's strength in this case). Their getting one gulp by accident is not a problem.

As a point of reference, the LD50 level for hypochlorite is 5800 mg/kg so even a 50 pound child would have to drink 347 gallons of 100 ppm FC pool water to have a 50% chance of dying. The EPA notes the following in this link (http://www.epa.gov/chemfact/s_chlori.txt):


No adverse effects were noted in persons ingesting water containing 50-90 ppm of chlorine (~1.4 to 2.6 mg Cl/kg/day) for a short periods of time (U.S. EPA 1989). Drinking water concentrations of >90 ppm chlorine caused irritation of membranes of throat and mouth (U.S. EPA 1989). Concentrations of chlorine in the drinking water of greater than 25 ppm make the drinking water unpalatable (U.S. EPA 1989).
Even the irritations they note of the throat and mouth would not happen when there is CYA in the water since it would significantly slow down chlorine reaction rates.

[PoolDoc]

As a point of reference, the LD50 level for hypochlorite is 5800 mg/kg so even a 50 pound child would have to drink 347 gallons of 100 ppm FC pool water to have a 50% chance of dying.

Thanks Chem_Geek. And, to put that 347 gallons in perspective, about 20 years ago a lady accidentally drank about 4 oz. of bleach, after setting her juice glass next to a glass which had bleach in it. She then panicked and drank 2 gallons of water to 'dilute' the bleach. The bleach wouldn't have hurt her, but the water killed her, by so diluting the electrolytes in her body.

So, a child COULD NOT drink that much water -- they would die from over hydration long before the chlorine could have any effect.

[JimK]

So it's apparent that chlorine would have to be very high to hurt us, but what about our bathing suits? For example, if my CYA is 80, what would the maximum FC level recommended to avoid destroying my bathing suit?

[PoolDoc]

No good answer to that: the most expensive women's suits are almost completely intolerant of chlorine.

I can tell you that very expensive women's suits are worse than moderate ones, and that suits with elastic (Lycra) are much worse than nylon board shorts or guard suits . . . and that 100% polyester competition suits last forever. But other than that, you have to experiment. However, if you are asking the question, I'd recommend separating your family's suits into "swimming suits" and "showing off suits". If you do that, you'll likely end up with the more chlorine resistant ones in the swimming pile.

I have some OLD (20 year old) data on grades of Lycra used in competition suits . . . and I can tell you that, at least back then, the most common Lycra elastic was sold on the presumption that women would 'slip and dip', not swim. I think the life expectancy was something like 5 hours at 3 ppm - and that the suit would last the summer. They didn't consider or test stabilized chlorine solutions.

[JimK]

No good answer to that: the most expensive women's suits are almost completely intolerant of chlorine.

I can tell you that very expensive women's suits are worse than moderate ones, and that suits with elastic (Lycra) are much worse than nylon board shorts or guard suits . . . and that 100% polyester competition suits last forever. But other than that, you have to experiment. However, if you are asking the question, I'd recommend separating your family's suits into "swimming suits" and "showing off suits". If you do that, you'll likely end up with the more chlorine resistant ones in the swimming pile.

I have some OLD (20 year old) data on grades of Lycra used in competition suits . . . and I can tell you that, at least back then, the most common Lycra elastic was sold on the presumption that women would 'slip and dip', not swim. I think the life expectancy was something like 5 hours at 3 ppm - and that the suit would last the summer. They didn't consider or test stabilized chlorine solutions.

I see. So when shopping for a "pool suit", I should look for nylon or polyester and try to minimize/avoid lycra. We're too cheap to buy expensive suits, so guess we should be fine with the recommended "best guess" levels.

[chem geek]

Just keep in mind that it is the active chlorine (hypochlorous acid) that attacks the swimsuit, not the Free Chlorine (FC) level. So when there is CYA in the water, the rate of attack is orders of magnitude slower. My wife experiences this effect every year when she uses an indoor commercial pool where the elasticity in her swimsuits gets shot after one winter season and her skin is somewhat flaky and hair frizzy until she takes a shower while in our own outdoor residential pool the swimsuits last for years and there aren't the same side effects with skin and hair. The main difference is that the indoor pool has 1-2 ppm FC with no CYA while our outdoor pool has 3-6 ppm FC with 40 ppm CYA which has an active chlorine level similar to around 0.1 ppm FC with no CYA. So the active chlorine level of the indoor pool is 10-20 times higher and oxidizes swimsuits, skin and hair that much faster as well.

The higher FC level does have an effect after you get out of the pool in that there is more chlorine in reserve so that it can keep reacting for longer as the water evaporates, but this effect can be minimized by rinsing the suits and is generally less important that the active chlorine level.

[JimK]

Thanks.

So a related question;

If I remember correctly, with my CYA at 80, the recommended shock level is 20. How much should I allow it to drop before swimming again?

[PoolDoc]

Women's fashion suits might want to wait till it's 15 or so. You just need to wait long enough for it to mix, so it's 20 all over, instead of 10 in most places and 40 near the returns. If you add it via bleach poured around the pool . . . 15 minutes should be plenty.

With a CYA of 80, 20 ppm is not going to have ill effects on swimmers.

[JimK]

Women's fashion suits might want to wait till it's 15 or so. You just need to wait long enough for it to mix, so it's 20 all over, instead of 10 in most places and 40 near the returns. If you add it via bleach poured around the pool . . . 15 minutes should be plenty.

With a CYA of 80, 20 ppm is not going to have ill effects on swimmers.

Thanks Ben. If I understand you correctly, if I follow my usual practice of shocking (I use cal hypo; pre disolved and poured throughout the pool) in the evening and letting the pump run all night, then it's OK to start swimming the next morning/day?

[PoolDoc]

Sure! It's also OK to swim that EVENING.

Using cal hypo? High calcium and SWCGs don't play well together.

Do you have a K-2006?
Do you know how to MANUALLY clean your DE filter?
Is your SWCG DOWNSTREAM of your filter?If the answer to all those questions is yes, you might want to use an alternative method of dosing with cal hypo that will limit the calcium build-up in the pool. Meanwhile, you need to know where your calcium levels are at present.

[JimK]

Sure! It's also OK to swim that EVENING.

Using cal hypo? High calcium and SWCGs don't play well together.

Do you have a K-2006?
Do you know how to MANUALLY clean your DE filter?
Is your SWCG DOWNSTREAM of your filter?If the answer to all those questions is yes, you might want to use an alternative method of dosing with cal hypo that will limit the calcium build-up in the pool. Meanwhile, you need to know where your calcium levels are at present.

I don't have that exact kit, but I have a few kits. One is a Taylor kit that I use to measure PH and TA (using R0014 reagent for PH, and R0007/R0008/R0009 for checking TA), another is a Taylor K1515-C (FAS-DPD Chlorine test), and a Tayor kit to test CYA level (using R0013 reagent), also a Jack's Magic Sequest kit, LaMotte test strips for borates, and most recently Aquacheck test strips for checking salt level (glad to report that the salt reading from the test strip reads almost the same as the SWCG display; gives me confidence my salt level is good). I did have a Taylor kit for checking calcium levels, but I had difficulty seeing the color change, so I returned it.

I do have calcium checked 2-3 times a season (May through Sept/Oct here). I checked my records since 2004 and calcium level has always been in the 200-250 range. I've never had any scaling on the salt cell or other parts since having the pool installed in 2004. It seems we get enough rain here to keep calcium levels from building too much. It's not uncommon that we will get enough rain in one storm that requires pumping excess water out of the pool. I haven't checked calcium yet this season (will do so soon), but I have no reason to think it will be any higher than usual. BTW, I've always used cal hypo to shock. Given this, is using cal hypo a problem?

I take the DE filter apart and manually clean it thoroughly at the end of each season. The salt cell is downstream (ie - after) the filter.

In my situation, do I need to be using an alternative method of dosing cal hypo (what is the alternative method??)?

Thanks again for your help. Your advice is greatly appreciated.

[PoolDoc]

If you've been using cal hypo, and have had stable chlorine over a full pool season, then no, it's not necessary to switch.

[PBLsQuad450]

Over the past 3 summers I have a tended my pool with over 300ppm CYA and under 30ppm of CYA. I loved reading this thread. I think the pool was much easier and more affordable to operate when the CYA was in the 70-80 range. Obviously I was keeping the Cl at a level appropriate to the CYA according to your table. I had zero problems and I suspect that high doses of Cl (40ppm) combined with 70-80 CYA was a fabulous pool closing combo. My lame (I am a social worker not a chemist) theory was that the CYA would maintain a higher Cl level longer making the early Fall, where it is more likely warmer, more protected from Algae. The colder months should have under the cover temps below 50. So, open the pool early and have it be blue? I think it worked... Granted, I have a 12 year old liner I'm not much concerned about. But the same theory (40ppm) to close worked with my CYA at 38 last year? Is the cover the reason, does a covered pool lose Cl THAT much slower because you shield it from the sun? I have a solid cover by the way. And there is still algae to kill on opening but it is pretty darn good compared to the old days of the closing company broadcasting 2lbs. Of Cal Hypo and covering.

I think, regarding the daily operation of my pool, that the 70-80 CYA level made my life the easiest. I see no difference in Cl smell or damage to suits or hair. So, if my observations are reasonable, it leaves behind the question of whether higher level CYA exposure is damaging us in any way?

[chem geek]

An opaque cover will block the UV in sunlight and have the chlorine last a lot longer. The colder water temperatures also slow down all chemical reactions including those that use up chlorine. In my own pool that has a mostly opaque electric safety cover, my chlorine loss rate with no bather load is around 0.7 ppm FC per day at 88ºF (with bather load and opening the pool every day for 1-2 hours the loss is closer to 1 ppm FC), but at 50ºF over the winter this drops to somewhat less than 0.1 ppm FC per day (about 1 ppm FC every couple of weeks). This is with the FC at around 10% of the CYA level and the CYA at 30 or 40 ppm (depending on season) though it gets diluted from winter rain overflow that I intentionally do (pool pump on cover pumps water into the pool and overflows from under the cover to an overflow drain.

If you truly have an opaque cover, then you should not need to have your chlorine start out that high if the water temp is cold when you close in winter and when you open again in spring. Usually, people only need to do that if their cover is not opaque because sunlight will continue to break down chlorine. Note that sunlight breakdown of chlorine is independent of temperature so having an opaque cover is important if one isn't going to be adding chlorine over the winter and wants to open up the pool algae-free.

[CarlD]

I don't have that exact kit, but I have a few kits. One is a Taylor kit that I use to measure PH and TA (using R0014 reagent for PH, and R0007/R0008/R0009 for checking TA), another is a Taylor K1515-C (FAS-DPD Chlorine test), and a Tayor kit to test CYA level (using R0013 reagent), also a Jack's Magic Sequest kit, LaMotte test strips for borates, and most recently Aquacheck test strips for checking salt level (glad to report that the salt reading from the test strip reads almost the same as the SWCG display; gives me confidence my salt level is good). I did have a Taylor kit for checking calcium levels, but I had difficulty seeing the color change, so I returned it.

With the test kits you have, you have the equivalent of the K-2006. The FAS-DPD test in the K-2006 is the same as the K-1515-C you have. The pH test is the same, too. As is the TA and CYA tests. You are fine that way.

[JimK]

With the test kits you have, you have the equivalent of the K-2006. The FAS-DPD test in the K-2006 is the same as the K-1515-C you have. The pH test is the same, too. As is the TA and CYA tests. You are fine that way.

Yeah, I would buy individual kits as I learned what to test and gained confidence doing it myself.

It would be more convenient having everything in one box, but it would be cheaper just to buy a small tacklebox for that purpose rather than buying a new K-2006 kit. ;)