Familiar with the recommendations for FC in normal use and in SLAMing. Coming from older methods of tracking chems, and the advice always seemed to be to prevent pool use when shocking until FC returned to normal levels. Of course TFP recommends higher normal levels (due to CYA) than old methods. But that begs the question - how much is too much for swimming? Any authoritative (even if conservative) information out there - tried various NIH, CDC, local Health Departments, etc. and haven't seen what would be considered a "safe" upper limit.
How much FC is too much?
- Thread starter sande005
- Start date
- Feb 6, 2015
- 6,236
- Pool Size
- 12300
- Surface
- Plaster
- Chlorine
- Salt Water Generator
- SWG Type
- CircuPool RJ-45 Plus
Anywhere between minimum and SLAM level for FC, based on your CYA level - see the FC/CYA Levels.
'Old methods' without accurate testing, and understanding the FC/CYA relatiomship equated to what we like to call 'dump and pray'.
So yes. Those methods were worried about unsafe levels, with no idea what unsafe was, or where you were.
Here we use precision and science to know exactly where you are, and where the safe window is. (Said above)
So yes. Those methods were worried about unsafe levels, with no idea what unsafe was, or where you were.
Here we use precision and science to know exactly where you are, and where the safe window is. (Said above)
Hence the question - are there references to the science concerning what the "safe" window is?
Trust but verify, and all that. Obviously at my CYA level of 25, a SLAM of about 11 ppm is a far, far cry from the old recommendations of 30ppm. So I'm not all that worried. But inquiring minds would like to know....
There are too many factors in determining a one size fits all 'safe' level once the FC gets above SLAM. Mustard Algae level was tested on finishes/equipment and proven to be safe for 24 hours, but there is zero real world need to maintain it longer than that. And as is, it's miserable enough to maintain for 24 hours because it burns off so quickly at the higher level.
Without mustard algae, there is zero real world need to be above SLAM FC. People overshoot a couple FC all the time and it's proven to be fine.
I understand your question and your reasons for asking it. I even applaud your wanting to get to the bottom of it, but there isn't an easy answer to point to. SLAM was designed to be the most effective and then was proven to be safe. The scientific process stopped then and there with no real world reason to go further.
Without mustard algae, there is zero real world need to be above SLAM FC. People overshoot a couple FC all the time and it's proven to be fine.
I understand your question and your reasons for asking it. I even applaud your wanting to get to the bottom of it, but there isn't an easy answer to point to. SLAM was designed to be the most effective and then was proven to be safe. The scientific process stopped then and there with no real world reason to go further.
- May 3, 2014
- 58,717
- Pool Size
- 6000
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- Fiberglass
- Chlorine
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- SWG Type
- Pentair Intellichlor IC-40
Pool Water Chemistry
This thread presents my findings so far on pool water chemistry including the following: More Accurate Calcite Saturation Index (CSI) to replace Langelier Saturation Index (LSI) Calculation of ppm HOCl (disinfecting chlorine) at various levels of Total Free Chlorine (FC) and Cyanuric Acid (CYA)...
www.troublefreepool.com
Dive in.
Thanks for the link to the detailed chemistry - I knew some, but this covered a lot more!
Interesting that there appears to be only anecdotal information on effects of various concentrations on swimmers. Lots of non-TFP recommendations, usually for 1 - 3ppm and never go above 6, or 8 or 9 or 10 - or everyone out of the pool! Apparently lots studied on how to kill stuff - how much, etc. for mustard algae and all. But not so much on adverse effects when going moderately high.
One would think that some agency would set cautionary upper limits, even if it is debatable by others with valid study/experience.
Google thumbnails quote the CDC as saying 10, but the page linked actually doesn't say anything about it at all.
Interesting that there appears to be only anecdotal information on effects of various concentrations on swimmers. Lots of non-TFP recommendations, usually for 1 - 3ppm and never go above 6, or 8 or 9 or 10 - or everyone out of the pool! Apparently lots studied on how to kill stuff - how much, etc. for mustard algae and all. But not so much on adverse effects when going moderately high.
One would think that some agency would set cautionary upper limits, even if it is debatable by others with valid study/experience.
Google thumbnails quote the CDC as saying 10, but the page linked actually doesn't say anything about it at all.
Saturn94
Bronze Supporter
- Mar 11, 2015
- 1,752
- Pool Size
- 20000
- Surface
- Vinyl
- Chlorine
- Salt Water Generator
- SWG Type
- Hayward Aqua Rite (T-15)
A FC number without a corresponding CYA number is meaningless. Without any CYA, FC can get harsh quite quickly, hence the generally low FC numbers you see from most places who don’t take the FC/CYA relationship into consideration.
As you look deeper into this (I’ve been down this rabbit hole and back so maybe I can save you a step or two), first off recognize you are headed down the ski slope with the other skiers but veering off the marked trails — do at your own risk. A logical starting point might be what we “know.” Assuming no CYA, WHO limits FC to 5 ppm for drinking (which is not “safe” but the benefits outweigh the risks) and some study (can’t remember offhand) found that about 10 ppm FC is a threshold for swimmer irritation. So, since I assume nobody will be drinking large quantities of pool water, let’s say the FC limit with no CYA is 10 ppm. Recall that at pH 7.5, we’d expect that to result in 5 ppm HOCL and 5 ppm OCL (before it starts doing what it does to pathogens and organics).
Now we can examine FC equivalence when we do have CYA. What level of FC with say 30 ppm CYA equates to 5 ppm HOCL with no CYA? With quick reference to chem geek’s chart, based on his equilibrium equations, which are based on O’Brien’s work, somewhere around 25 ppm FC would get you 5 ppm HOCL. https://www.troublefreepool.com/~richardfalk/pool/HOCl.htm
But we have a problem. If we have 5 ppm HOCL and 5 ppm OCL, at 25 FC with 30 CYA, then the leftover is 15 ppm of the various species of chlorinated isocyanurates (I’m sure this is oversimplifying but the concept is adequate for purposes here). Apparently not harmful, they are very irritating. https://www3.epa.gov/pesticides/chem_search/reg_actions/reregistration/fs_G-21_1-Sep-92.pdf
So then it’s like, ok, how much irritating is too much? And so it goes . . .
If you look at the SLAM FC chart, around half our hypothetical max of 25 FC at 30 ppm CYA is the recommended FC level (12 ppm). This does make sense as a compromise max where HOCL is going to be well above the 0.05 ppm level to kill algae (I think around 5x safety factor for the kill), but the other stuff in the water isn’t going to give your eyeballs what feels like an acid wash.
This is where I got to with it. Like you, I need to understand why I’m doing what I’m doing and the folks here were very helpful in facilitating my present level of understanding (which may still be wrong but I’m at where I’m at so far).
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THANK YOU! Your notes give me a reasonable basis for reassuring the various household members that I am not adding "too much" and they can go ahead and use the pool! And thankfully, I am already years past in my learning curve from when the pool store told me to "shock" it to 30 ppm FC!