Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 13 of 13

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

  1. Back To Top    #1

    Join Date
    Jun 2011
    Location
    West Central Florida
    Posts
    11

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

    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?

    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 or "bodily harmed". Who's right? And how much lithium hypochlorite should I add?

    Thanks!
    18,000 gallon in-ground oasis shaped, PebbleTec surface, connected spa; Pentair IntelliFlo VS pump; IntelliChlor SWG; Pentair Clean & Clear 150 sqft Cartridge Filter; Pentair heater

  2. Back To Top    #2

    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.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

  3. Back To Top    #3
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    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.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  4. Back To Top    #4
    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    Location
    SouthWest Alabama
    Posts
    22,333

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

    What they both said! ^^^

    Dang slow typing!
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

  5. Back To Top    #5

    Join Date
    Jun 2011
    Location
    West Central Florida
    Posts
    11

    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)?
    18,000 gallon in-ground oasis shaped, PebbleTec surface, connected spa; Pentair IntelliFlo VS pump; IntelliChlor SWG; Pentair Clean & Clear 150 sqft Cartridge Filter; Pentair heater

  6. Back To Top    #6
    dmanb2b's Avatar
    Join Date
    Apr 2009
    Location
    NY
    Posts
    3,728

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

    Welcome to TFP

    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
    24'x52" AGP (13,500 Gallons), Intex SWG, (2)Solar Bear 4x20 panels, Hayward S220T Filter, 1/2hp Pentair Superflo

    Pool School, TFTestKits, Pool Calculator

  7. Back To Top    #7
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

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

    Take a look at the first chart in this topic, keeping in mind that it is plotted on log-log axises.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

  8. Back To Top    #8

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

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

    Quote Originally Posted by Kermiter
    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)
    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.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  9. Back To Top    #9

    Join Date
    Aug 2010
    Location
    Dallas, TX
    Posts
    4,052

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

    Quote Originally Posted by Kermiter
    And how much lithium hypochlorite should I add?
    Are you just using some you already had and are about to make the switch to Clorox?
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
    If TFP has helped you, please click to SUPPORT TFP!

  10. Back To Top    #10

    Join Date
    Jun 2011
    Location
    West Central Florida
    Posts
    11

    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).
    18,000 gallon in-ground oasis shaped, PebbleTec surface, connected spa; Pentair IntelliFlo VS pump; IntelliChlor SWG; Pentair Clean & Clear 150 sqft Cartridge Filter; Pentair heater

  11. Back To Top    #11

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

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

    As shown in this Cost Comparison of Chlorine Sources, lithium hypochlorite is the most expensive source of chlorine about 5-6 times more expensive than chlorinating liquid, bleach or Cal-Hypo on a per FC basis.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

  12. Back To Top    #12

    Join Date
    Jun 2011
    Location
    West Central Florida
    Posts
    11

    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 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.
    18,000 gallon in-ground oasis shaped, PebbleTec surface, connected spa; Pentair IntelliFlo VS pump; IntelliChlor SWG; Pentair Clean & Clear 150 sqft Cartridge Filter; Pentair heater

  13. Back To Top    #13

    Join Date
    Mar 2007
    Location
    San Rafael, CA USA
    Posts
    12,082

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

    Quote Originally Posted by Kermiter
    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.
    Your welcome. There are many great contributors on this site and many chip in to help out each other when they can.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •