How much FC is too much?

Jump to latest Follow Reply
K

KevinL

Bronze Supporter
Apr 29, 2023
57
Long Beach, CA
My pool CYA is at 45 ppm. According to "trouble-free pool recommended FC levels" (Free Chlorine and Cyanuric Acid Relationship Explained) I'm supposed to maintain at least 6 ppm FC. Now, on a sunny day, I lose about 3 ppm FC. Therefore, when adding chlorine every other day, my target FC is 6 + 3 + 3 = 12 ppm. It's a high concentration, and that's what I'm curious about.

I'd like to know what is the maximum free chlorine that you folks would allow your visitors to swim in. I've read a number of comments on this website from people who are not at all concerned about swimming in higher FC concentrations -- up to and including SLAM levels.

So what is your personal max FC ppm, and why?
 
  • Like
Reactions: RLP, Mdragger88 and KevinL
KevinL said:
My pool CYA is at 45 ppm. According to "trouble-free pool recommended FC levels" (Free Chlorine and Cyanuric Acid Relationship Explained) I'm supposed to maintain at least 6 ppm FC. Now, on a sunny day, I lose about 3 ppm FC. Therefore, when adding chlorine every other day, my target FC is 6 + 3 + 3 = 12 ppm. It's a high concentration, and that's what I'm curious about.

I'd like to know what is the maximum free chlorine that you folks would allow your visitors to swim in. I've read a number of comments on this website from people who are not at all concerned about swimming in higher FC concentrations -- up to and including SLAM levels.

So what is your personal max FC ppm, and why?
Click to expand...
It’s safe to swim all the way up to and including SLAM level. The chlorine tests can’t distinguish between chlorine that’s free to oxidize and the chlorine that’s bound up with CYA so it reports it as “high” but the active chlorine is actually quite low. That’s the reason for the chart and why you can get algae with CYA100 and you only have 5ppm of free chlorine. I’ve swam when the FC was 12-ish.
 
  • Like
Reactions: KevinL
Bperry said:
It’s safe to swim all the way up to and including SLAM level. The chlorine tests can’t distinguish between chlorine that’s free to oxidize and the chlorine that’s bound up with CYA so it reports it as “high” but the active chlorine is actually quite low. That’s the reason for the chart and why you can get algae with CYA100 and you only have 5ppm of free chlorine. I’ve swam when the FC was 12-ish.
Click to expand...

Did you notice any unappealing qualities to the high FC pool water?
 
KevinL said:
Did you notice any unappealing qualities to the high FC pool water?
Click to expand...
Nope. Been doing it for 3 years now. Usually swim when it’s around 6-8ppm only because the pH test doesn’t work so good when the FC is above 10.

If you don’t have enough CYA in the water then chlorine that high wouldn’t be good to swim in.
 
KevinL said:
Did you notice any unappealing qualities to the high FC pool water?
Click to expand...

Nope, no one can tell.

With water following TFP recommendations no one knows what the FC level is except for the person doing the tests.
 
  • Like
Reactions: RLP and Bperry
Tap water with 0 CYA and 1 ppm FC is harsher than SLAM FC, and tap water may have **up to 4 ppm FC**. And you drink that tap water. Err. Many, myself included don't, but we could in a pinch, and we DO shower/bathe in it.

But the industry doesn't recognize the CYA/FC relationship so to them, a 20 FC is insane. All of their 'over 3ppm is harsh' recs don't account for science. As such, they are modern day old wives tales which have long been disproven.
 
  • Like
Reactions: KevinL, RLP and xDom
ajw22 said:
Nope, no one can tell.

With water following TFP recommendations no one knows what the FC level is except for the person doing the tests.
Click to expand...
I would add one caveat to this. At high FC levels (approaching SLAM), I can notice a SUBSTANTIAL smell of chlorine on any towels used for drying off. It may be the chloramines due to the chlorine oxidizing the organics in the towel, or something else. Whatever it is, it's not super pleasant. At lower/normal FC levels (usually 6-10 FC for me), there is zero smell on the towels.
 
  • Like
Reactions: KevinL and Mdragger88
AW139 said:
At high FC levels (approaching SLAM), I can notice a SUBSTANTIAL smell of chlorine on any towels used for drying off. It may be the chloramines due to the chlorine oxidizing the organics in the towel, or something else. Whatever it is, it's not super pleasant. At lower/normal FC levels (usually 6-10 FC for me), there is zero smell on the towels.
Click to expand...
I imagine an argument could be made that at normal levels, a thin film of normally chlorinated water on you has been burned off by the time you get the towel thanks to your body oils/ sweat / bacteria/ etc, but with SLAM water it still has some left which then reacts with the residual laundry detergent / softener in the towel.

I use the pool as a poor man's shower often, either straight from work (as a prelude to a real shower) or mid yard project and I'll usually smell it at those times when I get out, with normal FC levels.
 
Newdude said:
I imagine an argument could be made that at normal levels, a thin film of normally chlorinated water on you has been burned off by the time you get the towel thanks to your body oils/ sweat / bacteria/ etc, but with SLAM water it still has some left which then reacts with the residual laundry detergent / softener in the towel.

I use the pool as a poor man's shower often, either straight from work (as a prelude to a real shower) or mid yard project and I'll usually smell it at those times when I get out, with normal FC levels.
Click to expand...
That's plausible for sure.

Jumping into the pool after doing lawn work is like 90% of the reason I installed a pool. I mow the lawn exclusively in swim shorts now, so as soon as I'm finished I go directing into the pool to cool off and relax.
 
  • Like
Reactions: KevinL, Mdragger88 and Newdude

Enjoying this content?

Support TFP with a donation.

Give Support
KevinL said:
Did you notice any unappealing qualities to the high FC pool water?
Click to expand...
Nope. The "unappealing qualities" like smell and burning eyes comes from CC which is created when your FC is attacking something. By keeping your FC within range your FC deals with contaminants real time so they cannot grow in your pool and ultimately keeps your CC low.

If you look at my avatar, that is my chlorine test which is usually a nice shade of dark orange and way off the yellow scale. My MIL always rants and raves about how much better my pool is than theirs since I "don't use chlorine". I just smile and say thank you at this point.
 
  • Like
Reactions: RLP, KevinL, Mdragger88 and 1 other person
Newdude said:
Tap water with 0 CYA and 1 ppm FC is harsher than SLAM FC, and tap water may have **up to 4 ppm FC**. And you drink that tap water. Err. Many, myself included don't, but we could in a pinch, and we DO shower/bathe in it.

But the industry doesn't recognize the CYA/FC relationship so to them, a 20 FC is insane. All of their 'over 3ppm is harsh' recs don't account for science. As such, they are modern day old wives tales which have long been disproven.
Click to expand...
Well said. Thank you.
 
  • Like
Reactions: Newdude
JJ_Tex said:
Nope. The "unappealing qualities" like smell and burning eyes comes from CC which is created when your FC is attacking something. By keeping your FC within range your FC deals with contaminants real time so they cannot grow in your pool and ultimately keeps your CC low.

If you look at my avatar, that is my chlorine test which is usually a nice shade of dark orange and way off the yellow scale. My MIL always rants and raves about how much better my pool is than theirs since I "don't use chlorine". I just smile and say thank you at this point.
Click to expand...


You're saying that you're free chlorine is way off the instrument's scale, but since you've got the correct ratio of CYA to FC, the free chlorine that she detects is minute and not noticeable.
 
  • Like
Reactions: JJ_Tex and Newdude
KevinL said:
You're saying that you're free chlorine is way off the instrument's scale, but since you've got the correct ratio of CYA to FC, the free chlorine that she detects is minute and not noticeable.
Click to expand...
058a4e03-3561-4790-8704-a06b910a8c21_text.gif
 
KevinL said:
You're saying that you're free chlorine is way off the instrument's scale, but since you've got the correct ratio of CYA to FC, the free chlorine that she detects is minute and not noticeable.
Click to expand...
HOCl, pH and CC the most common causes of irritation. If you keep pH in the 7s and CC < 1, you've eliminated the majority of irritations (skin/eyes).

HOCl is the stuff that bleaches suits and irritates. HOCl levels are dependent on FC and CYA levels...

FC 1.1 and CYA 0 = 1ppm HOCl
FC 16 and CYA 50 = .2ppm HOCl ... about 20% of the FC 1.1 and CYA 0 HOCl levels.

HOCl.gif
 
Last edited:
  • Like
Reactions: KevinL, Bperry and Newdude
Funny story…..
I was doing a slam & suspected Mustard algae so after we were done pooling for the day I raised fc to MA slam level thinking pool time was done (i had passed all the 3 criteria that morning).
I believe it was 41ppm fc at that time as my average cya is 70.
Ffw 30 minutes maybe & My hubby goes for a soak in the hot tub (separate body of water). I don’t think anything of it. Well, it apparently got too hot so he gets in the pool before I can catch him. He almost never gets in the pool.
I run out there & ask him how it feels/smells - he’s like “ Oh, it’s fine, feels good 👍🏻 “ totally oblivious. I told him how high the fc was & he honestly didn’t believe it I don’t think.
He has very sensitive skin so I checked with him later and no rash/irritation at all. I did instruct him to rinse his suit in the shower but we normally do that anyway after using the hot tub.
Now, I am in no way recommending people swim at MA slam levels but it won’t melt your skin off or anything.
As far as regular slam level goes I have been in the pool many times for extended periods and no problems. I do rinse my suit afterwards.
 
  • Like
Reactions: RLP, Newdude and KevinL
PoolStored said:
HOCl, pH and CC the most common causes of irritation. If you keep pH in the 7s and CC < 1, you've eliminated the majority of irritations (skin/eyes).

HOCl is the stuff that bleaches suits and irritates. HOCl levels are dependent on FC and CYA levels...

FC 1.1 and CYA 0 = 1ppm HOCl
FC 16 and CYA 50 = .2ppm HOCl ... about 20% of the FC 1.1 and CYA 0 HOCl levels.

HOCl.gif
Click to expand...
Your graph definitely illustrates that slam levels of FC Should not cause any discomfort. So just keep pH in the 7s and CC < 1. Those are very good guidelines, thank you.
 
  • Like
Reactions: AW139 and PoolStored
Mdragger88 said:
Funny story…..
I was doing a slam & suspected Mustard algae so after we were done pooling for the day I raised fc to MA slam level thinking pool time was done (i had passed all the 3 criteria that morning).
I believe it was 41ppm fc at that time as my average cya is 70.
Ffw 30 minutes maybe & My hubby goes for a soak in the hot tub (separate body of water). I don’t think anything of it. Well, it apparently got too hot so he gets in the pool before I can catch him. He almost never gets in the pool.
I run out there & ask him how it feels/smells - he’s like “ Oh, it’s fine, feels good 👍🏻 “ totally oblivious. I told him how high the fc was & he honestly didn’t believe it I don’t think.
He has very sensitive skin so I checked with him later and no rash/irritation at all. I did instruct him to rinse his suit in the shower but we normally do that anyway after using the hot tub.
Now, I am in no way recommending people swim at MA slam levels but it won’t melt your skin off or anything.
As far as regular slam level goes I have been in the pool many times for extended periods and no problems. I do rinse my suit afterwards.
Click to expand...
Great anecdote, thank you.
 
You must log in or register to reply here.
Thread Status
Hello , This thread has been inactive for over 60 days. New postings here are unlikely to be seen or responded to by other members. For better visibility, consider Starting A New Thread.
Top Bottom
Back
Jump to latest Follow Reply