safe FC and CC levels for swimming?

[SandyA]

Hi. I've made the switch from Bacquacil to chlorine (using BBB method) last fall before closing our pool for the season therefore am somewhat of a newbie to chlorine pool chemistry. What knowledge I've gained is thru extensive reading of poolsolutions.com threads.

Today I had to shock the pool to reduce the CC from .8 and my questions are:

1) When is the optimum time to shock in order to reduce pool shutdown (kids were heart broken....today was 90 degrees!)

2) At what minimum and maximum levels of FC and CC safe for swimming while adjusting to optimal values, especially when shocking the pool is necessary. For example, I've read in poolsolutions.com that if water > .5 CC a shock treatment is recommended but if the value is still low enough to swim in, I'd prefer wait to add bleach and shock treat later in the evening while the pool is not in use. EDITED TO ADD: Or, if shocking is absolutely necessary, at what level FC can the kids jump in the pool after shocking.

Thank you.

 

[JasonLion]

A CC level of .5 is not a big deal, perhaps a little smell. The safe chlorine level totally depends on your CYA level. Could you post all of your number? That we allow us to help you much more effectively.

 

[SandyA]

Wow. I didn't expect an answer so quickly. Thx!

The sample taken to a local pool store had a reading of 37ppm CYA. From my Taylor DPD-FAS, it's more like 25 (where I'd rather be).

At that level of CYA, what level of FC is OK to go back in the water? I'm assuming that it has to drop below shock value. Yes? Also, do you know the maximum CC level recommended for swimming? I'd prefer to wait to shock later in the evening if the value is still within safe range (but obviously, not optimal) or should we stay out of the pool at all values above .5ppm CC until it is lowered?

Thanks again.

 

[Buggsw]

Generally, you read that between 2 - 4 of FC. But those figures are under the assumption that everything else is in a certain "recommended" range, too.
Here's a chart that was compiled by Ben? over at poolsolutions. It's his "best guess" chart. It's been copied here before, so I hope it's okay for me to do so as well.

Stabilizer . . . . . . Min. FC . . . . Max FC . . . 'Shock' FC
=> 0 ppm . . . . . . . 1 ppm . . . . . 3 ppm . . . . 10 ppm
=> 10 - 20 ppm . . . . 2 ppm . . . . . 5 ppm . . . . 12 ppm
=> 30 - 50 ppm . . . . 3 ppm . . . . . 6 ppm . . . . 15 ppm
=> 60 - 90 ppm . . . . 5 ppm . . . . . 10 ppm . . .. 20 ppm
=> 100 - 200 ppm . . . 8 ppm . . . . . 15 ppm . . .. 25 ppm

So, the next time you shock, if the free chlorine is in the safe range (in the Min/Max range for your CYA level - wait until the evening to shock, so the kiddies can cool off. It's best to shock at night, anyway. No sun makes it more effective.

 

[duraleigh]

Sandy, Personal preference (or stupidity) but I would not pass up a good day of swimming with somewhat elevated chlorine levels.

By comparison, when you put a cup of Clorox in your washing machine, You Cl goes to about 500ppm or higher (somebody check that math). I'm not suggesting you swim in your washer, (that rotor thingy will bump the heck out of you :lol: ) but you see how much less 20ppm in your pool is.

Prolonged exposure might fade a swim suit (wear an old one) but I think you can swim with absolutely no harm.

 

[SandyA]

Thank you so much for the info, Buggs and Dave. Good to know we have some leeway in the numbers for swimming.

I was beginning to think that Bacquacil had one advantage over bleach b/c we had to stay out of the pool. Guess not.

 

[Guest]

If your CYA is in the recommeded range of 30-50 ppm you can go in the water when the FC drops below 10 ppm.

 

[chem geek]

Believe it or not, 20.5 ppm FC with 30 ppm CYA is equivalent to 2 ppm FC with no CYA, at least as far as disinfecting chlorine levels are concerned. waterbear's advice is fine -- anything below 10 ppm FC in 30 ppm CYA (equivalent to 0.46 ppm FC with no CYA) should be fine. The main issue with the higher FC is if you drink the water since all of the chlorine, not just the disinfecting chlorine, will get ingested. The 10 ppm recommendation is safer in this regard.

 

[duraleigh]

Evan and Richard,

Help me understand your posts a little better. Why is it unsafe over 10ppm? Disregard the CYA affect for now, I'm not sure what chlorine levels are "safe" and who decided. What happens to you if you swim (swallow) at 15-20ppm?

 

[Guest]

Evan and Richard,

Help me understand your posts a little better. Why is it unsafe over 10ppm? Disregard the CYA affect for now, I'm not sure what chlorine levels are "safe" and who decided. What happens to you if you swim (swallow) at 15-20ppm?

Both the CPO study books in the state of Florida and this website http://www.deh.enr.state.nc.us/ehs/chem.htm list the maximum FC for entering either a pool or spa at 10 ppm. In the state of Florida commercials pools and spas can be entered by bathers when the FC or Bromine is below 10 ppm. Some states have lower limits on commercial pools and spa. The lowest I have seen is 5 ppm but most are at 8 or 10 ppm.

 

[lovingHDTV]

Evan and Richard,

Help me understand your posts a little better. Why is it unsafe over 10ppm? Disregard the CYA affect for now, I'm not sure what chlorine levels are "safe" and who decided. What happens to you if you swim (swallow) at 15-20ppm?

Both the CPO study books in the state of Florida and this website http://www.deh.enr.state.nc.us/ehs/chem.htm list the maximum FC for entering either a pool or spa at 10 ppm. In the state of Florida commercials pools and spas can be entered by bathers when the FC or Bromine is below 10 ppm. Some states have lower limits on commercial pools and spa. The lowest I have seen is 5 ppm but most are at 8 or 10 ppm.

Interesting read, I found this under the CYA heading:

"Excessive amounts of cyanuric acid can interfere with the disinfection process and at concentrations above 100 ppm may cause "chlorine lock" and clouding of the pool."

Seems to be totaly in line with what I've been reading on the boards here.

 

[chem geek]

This link lists some studies that showed toxicity limits for chlorine. Since chlorine gets released from CYA quickly (half-life of 0.25 seconds for one species; 4 seconds for another) ingesting chlorine with CYA should be treated as if the chlorine were without CYA, at least from a concentration point of view (i.e. the CYA slows down reactions by lowering effective disinfecting chlorine concentration, but the total chlorine "load" is based on the FC level).

10 ppm is a rather safe and conservative limit. Short-term exposure to higher levels probably won't cause any harm, but since you are talking about children and since they can ingest (swallow) pool water, it's better to play it safe than to be sorry so I'd follow the 10 ppm recommendation.

Richard

 

[lovingHDTV]

So how does this jive with the need to have >10ppm FC for high CYA? Does that mean you should never have CYA > 80ish os that you can keep FC count < 10ppm?

thanks,

 

[duraleigh]

I am facing a hot day outside which I hate and that thought has put me in a cantankerous mood. From chemgeek's always very thorough and well-thought post:

Fidler (1977)
This study found a decrease in the number of peritoneal macrophages in mice only when
the chlorine level was raised to 25 to 30 ppm. No adverse effect was observed when the
chlorine level was 12 to 16 ppm.
Hermann (1982)
The purpose of this study was to determine if chronic ingestion of drinking water containing
30-ppm chlorine could change the in vivo immune responses in mice. Overall, no
significant effect was observed.
DeZuane (1990)
DeZuane states that chlorine in water is fatal at 1,000 ppm, but that “consumption of
drinking water containing 50 mg/L of chlorine has produced no adverse effect.”

Richard, what the heck is "peritoneal macrophages" and do we really need them?

Secondly, if this guy DeZuane say 1000ppm will kill you, that means (if I did the math right) that a normal washing machine contains fatal doses of Cl. Seems like Clorox would've had some pretty massive lawsuits if Junior gets into the machine and drinks a cup.... :lol:

Lastly, I know this belongs somewhere over in the Geek section because it's not pertinent to maintaining a pool correctly, but I suspect government officials and scientists simply keep lowering the ppm if they publish anything just to be "conservative". Heck, my bottle of generic bleach I'm looking at doesn't even have the classic "Harmful or fatal if swallowed" warning on it....it says if you swallow it to drink some water (preferably, not from the washing machine!! :lol: )

So, here's what I suspect.... Somebody told this scientist guy he needed to determine a "safe" level of chlorine. The scientist guy had some mice drink the stuff and nobody dies. Unfortunately his grant ran out before he could figure out where the real toxicity levels were so, "just to be safe" he publishes a number...say 50ppm.

Next, the guy who asked the scientist reports to his boss and since his signature is on the report, he drops that number to 25ppm. The boss, who is about to retire in 6 months, tells him to change it to 10ppm, at least until he can retire and get that pension.....so 10-ppm gets published.

My last thought....since municipal drinking water is 2-3ppm in many places and you are encouraged to drink as much water as possible for all sorts of reasons...maybe even a gallon a day....which would be worse for you...a gallon of drinking water @ 2-3ppm or an occasional slurp of pool water @ 20ppm?

Yes, I understand I'm being a redneck and we should all be cautious.....as I said, it's gonna' be too hot outside for me today and I'm feeling very cranky :lol: :lol:

 

[chem geek]

Dave,

This link has some more info from WHO that is a little more clear, though it's focussed on sodium cyanurate, the end product when the chlorine has reacted (with saliva). So this report is looking more at cyanuric acid than chlorine. Remember that toxicology studies are looking at drinking water and you are absolutely right that we used to have chlorine in our drinking water (around 2 ppm FC or so, depending on how long it lasted in the distribution system) though now many systems have switched to monochloramine since it lasts longer and doesn't create as many disinfection by-products.

When I said that 10 ppm is safe and conservative, I literally mean that. You could drink far higher concentrations in a one-time dose and likely have nothing happen to you. Regular ingestion of the water would be the problem. But since children are the ones that tend to ingest pool water and since their bodies are smaller, the risk is higher. But the risk is very, very low.

There's not going to be a single answer here because toxicity (and ill effects long before death) is a probabilistic thing. In short, people should not be scared of their pools and the question was simply when it was safe to go into the water. If you don't drink the water, you could go in with far higher chlorine levels. If you drink it just a little and not often, then it's still safe. If you drink it a lot and it's at 20 ppm FC, then you may increase your risk but it's still far from toxic levels or any immediate problems.

As for washing machines, you generally don't drink washing water (as you point out). If you drank the Clorox straight, or any of a number of other household substances, it would likely prove fatal or certainly very harfmul to your body. My bottle of Clorox has the "IF SWALLOWED" description of what to do including contacting a poison center. If your bottle of a no-name brand doesn't, then they are being foolish because some young child somewhere might drink it (doubtful since it smells so strong, but you never know) if the parent didn't store it properly away from children.

Anyway, I agree with you that a slurp at 20 ppm is probably OK. Someone on another thread or forum asked about their dog that drank from the pool regularly and drank a lot. Typical chlorine levels (5 ppm FC or so) were below when first symptoms of any problems would occur, but having 50 ppm Borates was more of a problem -- not huge, but just over the edge of first symptoms in the most extreme study. The risk was very, very low, but this owner decided not to add the Borates in their particular situation. It's a personal decision.

Richard

 

[duraleigh]

Hi, Richard,

As always, I am completely impressed with your willingness to provide thorough, thoughtful answers. You are a real benefit to this board and those of us on it.......I hope you don't take offense when I do my "redneck" act.....I do it in good humor and, well, maybe to stir the pot a little

I do have a clearer understanding of what's safe as a result of your posts. Besides, I just took a dip in my sparkling pool (water temp - 82) and I'm not nearly as cantankerous as this AM. :lol:

As an aside, My two dogs and two cats use the pool as their main water source when they're too lazy to walk down the hill to the pond....my guess is their innards are sparkling clean.....they still smell like dogs and cats on the outside, however. :lol:

see ya'