Confused about safe FC level: Chlorox vs. Chlorine/CYA Chart

Jump to latest Follow Reply
K

Kermiter

0
Platinum Supporter
LifeTime Supporter
Jun 3, 2011
11
West Central Florida
I'm sorry if this has been answered already. I've been searching for awhile without luck...

Everything I've read in the Chlorine/CYA Chart thread makes a lot of sense. However, the Clorox Service Bulletin clearly states "Re-entry to treated pools is prohibited above 4ppm [available chlorine] due to risk of bodily harm." (p. 2)

Hmmm? Bodily harm? :pale:

FC: 0.83
TC: 1.00
pH: 7.7
TA: 94
CH: 187
CYA: 60
Pool: 15k, PebbleTec, bleach & lithium hypochlorite, Florida

I plan to add lithium hypochlorite this evening after the pH gets to around 7.2 (I added muriatic acid this morning.) My water is crystal clear and I have generally been keeping the FC around 2-3ppm.

According to the Chlorine/CYA Chart, my target FC should be 6.8ppm and I should never let it fall below 4.4ppm. (oops)

I (noob) am trying to reconcile the highly educated Chlorine/CYA Chart with Clorox's blunt warning. I'm guessing the answer will be that Clorox's calculation is based on zero CYA...? If so, can I then infer that my higher CYA level results in a lower "actual FC" (if there is such a thing)? For example, if FC reads 6.8ppm with CYA of 60, my "actual FC" is really only something like 3, and thus safe for swimming?

I'm just confused right now as to where I should maintain my FC level so that nobody gets sick :puker: or "bodily harmed". Who's right? And how much lithium hypochlorite should I add?

Thanks!
 
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

I believe that is true without any CYA in the water. But the CYA binds up chlorine so it is not all available at once.

One of the chemistry experts can explain better.
 
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

What anonapersona said :)

The "active chlorine" level is really the HOCl level, which varies with both the FC level and the CYA level. It takes extremely high FC levels when CYA is 40-50 to match the HOCl level you get at FC of 4 when CYA is zero.
 
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

Thanks for the helpful replies! I will start keeping higher FC levels based on the Chart.

Is there a formula to calculate the active chlorine (HOCl) level for a particular "CYA-adjusted" FC?

For example, with CYA = 60 and FC = 6.8, what would be my level of active chlorine? Certainly less than 4, right? But how much less?

Another way of asking is, if my CYA = 60, how much FC is needed to reach a particular level (e.g., 3ppm) of active chlorine (HOCl)? :scratch:
 
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

Welcome to TFP :wave:

Not sure about the active level, but a general rule of thumb is your target FC is roughly 10% of your CYA level. Said another way the level of active chlorine with CYA at 30 and FC of 3 is about the same as FC at 6 with CYA at 60 :goodjob:
 
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

Kermiter said:
However, the Clorox Service Bulletin clearly states "Re-entry to treated pools is prohibited above 4ppm [available chlorine] due to risk of bodily harm." (p. 2)
Click to expand...
They are required to say that by law in order to be EPA registered because the EPA drinking water limit for chlorine is 4 ppm and that is used as the basis for maximum chlorine levels with no understanding of CYA and its effects. Also, most counties and states ignore the EPA with regard to pool chlorine maximum levels with some allowing 10 ppm FC maximum (see this link for example), but that is to allow higher FC levels in outdoor pools where CYA is being used though the regs don't usually make that distinction clear. Most jurisdictions have a 5 ppm FC maximum, but again, no distinction is made regarding CYA. The CYA limit used to be 100 ppm, but many jurisdictions now limit it to 30 ppm and a few do not allow CYA at all.
 
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

Thanks again for all the great answers! Very helpful. I can use the ~10% rule of thumb and will examine the detailed "Deep End" report. :)

RobbieH, in answer to your question, I have used both. I prefer the powder to the liquid for handling/storage, and because I don't want the extra additives right now, I went with lithium hypo. I plan to add two 1lb bags tonight (15k gallon PebbleTec).
 

Enjoying this content?

Support TFP with a donation.

Give Support
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

Hi, chem geek. I did see your comparison, which actually helped me decide on the lithium hypochlorite. I switched to it for my month-new PebbleTec surface because (other than cost) there don't seem to be any downsides compared with the other granular forms, and it's easier for me to store than the liquid.

I don't want more calcium or stabilizer, and am so glad I learned about them before my numbers got too high. I plan to switch to a SWG in the next few weeks which is about when my current batch of li-hypo will run out. You're right, it's not cheap :eye: but I prefer it over transporting and storing the liquid chlorine. Still, I usually pick up a gallon or two of Clorox when I'm at the grocery store to help ease the cost pain. If/when I need to shock, I will likely do that with liquid (not Clorox), but so far my CC has never hit 0.2.

FC: 5.17
TC: 5.22
pH: 7.4
TA: 82
CH: 217
CY: 49
CSI: -0.27

By the way, in a very short period of time, I have gotten much out of your many incredibly helpful and informative contributions on this site. So, thank you for that.
 
Re: Confused about safe FC level: Chlorox vs. Chlorine/CYA C

Kermiter said:
By the way, in a very short period of time, I have gotten much out of your many incredibly helpful and informative contributions on this site. So, thank you for that.
Click to expand...
Your welcome. There are many great contributors on this site and many chip in to help out each other when they can.
 
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