Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 10 of 10

Thread: Accounting for CYA / ratio

  1. Back To Top    #1
    JohnA902's Avatar
    Join Date
    Apr 2016
    Location
    Baltimore MD
    Posts
    108

    Accounting for CYA / ratio

    So I have been searching for topics on what to do if a kid poops in the pool. ( hypothetical, thank goodness this hasn't happened). I found a bunch of good stuff, one link led me to the CDCs site which suggests "raising free chlorine to 2ppm for 30 min"

    That is confusing.

    Clearly they aren't accounting for cya. So how would one scale up their 2 ppm for a certain cya level. I'm familiar with the chlorine / cya chart so I know my own recommended levels but I was curious how this 2 would compare. Is 2 the CDCs shock level ignoring cya?

    I'm having trouble expressing my question. I guess I'm looking for a ratio? Or what assumption is the CDC making about cya? Then I could do the following ratio:

    cdc's cya / 2 ppm = my 40 cya / x ppm

    maybe the answer is right in that chlorine / cya chart but I'm just not connecting it.

    Thoughts?

    john
    27,000 gal concrete rectangle, built Oct '15, DE filter, Jandy PHPM 1.5 HP, Hayward HP21104T heat pump, TF-100

  2. Back To Top    #2
    ned8377's Avatar
    Join Date
    Apr 2015
    Location
    Wake Forest, NC
    Posts
    239

    Re: Accounting for CYA / ratio

    If some kid had diarrhea in my pool I would just dump a gallon of 12.5% bleach in. Then check FC and CC the next morning.
    True L 45,000 gal Hayward IG vinyl pool. Hayward Tristar 2.40 THP; 1.5 FRHP/1.60 SF. Hayward Model # S310T2 Sand Filter. Aqua Rite T-15. Aqua Comfort 154,000 BTU Heat Pump. TF-100

  3. Back To Top    #3
    Richard320's Avatar
    Join Date
    Jan 2010
    Location
    San Dimas, CA (LA County)
    Posts
    18,768

    Re: Accounting for CYA / ratio

    I think what you want is in this graph. Note that the scales are logarithmic.



    There's more to confound and amaze you in Pool Water Chemistry
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  4. Back To Top    #4

    In the Industry
    OTPirate's Avatar
    Join Date
    Oct 2013
    Location
    Creedmoor, NC
    Posts
    994

    Re: Accounting for CYA / ratio

    My thought is that you need some sanitizer in there immediately. I have seen a "code brown" literally, that is what they call it at public pools and no one tests the CYA. I would raise my FC to SLAM level and then check in the morning. It seems like it would almost be like having algae in your pool, maybe worse. Thoughts?

  5. Back To Top    #5
    JohnA902's Avatar
    Join Date
    Apr 2016
    Location
    Baltimore MD
    Posts
    108

    Re: Accounting for CYA / ratio

    Hmmm. That's a tough graph to extrapolate from. I guess I still want to know how to use their "2ppm" in a real world example of having 50 ppm cya.

    The idea of "raising to 2ppm" is meaningless when I'm already at 5.


    27,000 gal concrete rectangle, built Oct '15, DE filter, Jandy PHPM 1.5 HP, Hayward HP21104T heat pump, TF-100

  6. Back To Top    #6
    JohnA902's Avatar
    Join Date
    Apr 2016
    Location
    Baltimore MD
    Posts
    108

    Re: Accounting for CYA / ratio

    For the poop idea, I guess I would just raise to shock level (which is like 16 or so), let it circulate and then let the other kids back in after 30 min. Anyway, I just wanted a plan in case this happened.


    27,000 gal concrete rectangle, built Oct '15, DE filter, Jandy PHPM 1.5 HP, Hayward HP21104T heat pump, TF-100

  7. Back To Top    #7
    Mod Squad tim5055's Avatar
    Join Date
    May 2014
    Location
    Columbia, SC
    Posts
    8,499

    Re: Accounting for CYA / ratio

    Quote Originally Posted by JohnA902 View Post
    For the poop idea, I guess I would just raise to shock level (which is like 16 or so), let it circulate and then let the other kids back in after 30 min. Anyway, I just wanted a plan in case this happened.


    Sent from my iPhone using Tapatalk
    Good plan, that was along the lines of what I was going to suggest.
    TFP Moderator 39 X 18 23,000(ish) freeform gunite; built 2007ish; Pentair Triton II TR100 600lb Sand filter; 2 HP Pentair pump with 2.2 HP AO Smith single speed motor; 2 skimmers, 1 main drain, 4 returns w/waterfall, Stenner 45MHP2 3GPD running@ 60% - 15 gal Tank; heated by the sun CYA 200+ when I started - 50 now. Dolphin Supreme M5 Pool Cleaner. Hot Springs SX Spa, 285 gallon

  8. Back To Top    #8

    Join Date
    Aug 2013
    Location
    Otsego, MN
    Posts
    78

    Re: Accounting for CYA / ratio

    Looking at the CDC pdf document on the topic (found here: https://www.cdc.gov/healthywater/pdf...mendations.pdf), they delineate two responses, depending on if the stool is formed (not as dangerous) or diarrhea (much higher risk). For "formed stool incidents," disinfection times are based on killing Giardia cysts, while for "diarrheal incidents," times are based on killing Cryptosporidium (they explain why in the document).

    The 2ppm recommendation is for formed stool, and only if the existing chlorine concentration is less than 2 ppm. Additionally, you must "ensure pH 7.5 or less and a temperature of 77F (25C) or higher."

    The formed stool guidelines go on to say "State or local regulators may require higher free chlorine levels in the presence of chlorine stabilizers, which are known to slow disinfection."

    So, not great guidance on what to do about your CYA level there.

    However, in the diarrhea guidelines, they discuss stabilizer effects on disinfection further:

    "Raise the free chlorine concentration to 20 ppm and maintain pH 7.5 or less and a temperature at 77F (25C) or higher. The free chlorine and pH should remain at these levels for at least 12.75 hours to achieve the CT inactivation value of 15,300.
    Crypto CT inactivation values are based on killing 99.9% of Crypto. This level of Crypto inactivation cannot be reached in the presence of 50 ppm chlorine stabilizer, even after 24 hours at 40 ppm free chlorine, pH 6.5, and a temperature of 77F (25C). Extrapolation of these data suggest it would take approximately 30 hours to kill 99.9% of Crypto in the presence of 50 ppm or less cyanuric acid, 40 ppm free chlorine, pH 6.5, and a temperature of 77F (25C) or higher."

    To me, all this means the following:

    If it's formed stool in the pool, scoop out as much as possible immediately. Formed stool has less pathogenic bacteria than diarrhea, and it's fairly well contained. It sounds like your standard daily chlorine levels (for your CYA level) will kill the bacteria pretty quickly, but raising to shock level almost certainly will disinfect completely.

    If it's diarrhea, you're in for more of a battle. Higher chance of bad bacteria, more dispersed, etc. Scoop/bucket out what you can, and crank up the chlorine to high levels (beyond shock level for your CYA) for days. Fun.

    My two cents.
    Pool/Equipment: 20'x52" round Intex Ultra Frame AGP (~8,800 gallons)--Intex SWCG (CG-28669, 15K gallon model)--Intex Sand Filter Pump (SF60110, 16", 120lbs sand, 3K gph)--Hayward SP1091LX Through-Wall Skimmer--Hard Plumbing--Taylor K-1766 Salt Test Kit--TF-100 Test Kit

  9. Back To Top    #9
    JoyfulNoise's Avatar
    Join Date
    May 2015
    Location
    Tucson, AZ
    Posts
    11,632

    Re: Accounting for CYA / ratio

    I'll only add this point to what has been posted - you have to differentiate between a residential pool which is normally confined to one single family versus a public pool. All State, local & CDC recommendations and codes are going to apply to commercial/public pools which, in the event of a fecal incident, would more than likely shut down for the rest of the day. In some areas, the remediation & reporting requirements for a fecal exposure would require not only FC/pH data but also fecal coliform testing as well.

    In a residential pool setting, many of these guidelines make no practical sense because it would be a rare circumstance to find a family that has active cryptosporidium or giardia lamblia. Those are the two major, chlorine-resistant disease vectors that you have to worry about in pools with a fecal exposure. So, at then end of the day, if you have a fecal exposure in your pool, your best bet is to simply get everyone out of the pool and raise the FC up to shock level for 24 hours and then let it drift down naturally. Everyone can still swim at shock levels if they chose to.

    TFP advocates a method of pool care that puts the active chlorine level (which is proportional to the FC/CYA ratio) at a value which will destroy bacterial and viral pathogens very quickly. In a pool with no CYA and 2ppm FC (very harsh chlorine levels), the hypochlorous acid (HOCl) concentration would be close to 1ppm at a pH of 7.5. Normal bacteria and viruses are killed at HOCl concentrations of 0.01ppm, i.e. 100 times lower level than what is advocated in the CDC document but designed to be overkill to handle an exposure. With the TFPC Method of pool care (5-7.5% FC/CYA ratio), the HOCl concentration is ~0.05ppm or so. That is 5X what is needed to inactivate most pathogens. At shock level, the FC/CYA ratio is 40% so you would neutralize pathogens even more quickly.
    Matt
    16k IG PebbleTec pool, 650gal spa, spillway and waterfall, 3HP IntelliFlo VS / 1.5HP WhisperFlo, Pentair QuadDE-100 filter, IC40 SWCG, MasterTemp 400k BTU/hr NG heater, KreepyKrauly suction-side cleaner Dolphin S300i robot, EasyTouch controls, city water, K-1001, K-2006 and K-1766 test kits, Mannitol test for borates

  10. Back To Top    #10
    JohnA902's Avatar
    Join Date
    Apr 2016
    Location
    Baltimore MD
    Posts
    108

    Re: Accounting for CYA / ratio

    Thanks everyone. Good replies. Lots of info.


    27,000 gal concrete rectangle, built Oct '15, DE filter, Jandy PHPM 1.5 HP, Hayward HP21104T heat pump, TF-100

Posting Permissions

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