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Thread: FC vs CYA Question

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    FC vs CYA Question

    OK guys I have read through a lot of information here and have a question in regards to FC:

    I understand the TFPC chart of FC vs CYA and it makes a lot of sense, however, why is this not more readily available from other sources? I get confused as to why most test strip kits (I know they aren't accurate) and pool stores would tell you to maintain FC levels of 1-3ppm without regards to CYA levels? This would seem to be a bit short-sighted and cause major problems with pool water especially as CYA levels increase. I am 100% agreeing with the TFPC method and plan to follow this websites recommendation, so I am not doubting anything on TFP at all, this is more out of curiosity for my own mind LOL...
    22000gal IG plaster, Dallas, TX area (Feb 2016)
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    klynch494's Avatar
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    Re: FC vs CYA Question

    Just thinking out loud here... but maybe it has something to do with getting you back into the store to spend more money on their products that magically turn your water back to "crystal clear"...
    Kevin, TFP Believer & Supporter
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    Re: FC vs CYA Question

    One reason is that pool stores are in business to sell products with more markup than bleach and baking soda, etc. They are also primarily promoting the use of pucks to chlorinate, which constantly raises CYA (i.e. constantly changes the required FC). This concept would be impossible to effectively communicate to customers - many people don't want or care to know. Further, they may not really accept or buy into the theory behind the FC/CYA relationship. But mostly it's too hard for pool stores to quickly communicate those ideas to the masses and it's not a great business profit case. The philosophy here at TFP is understanding what you put into your pool and why. The philosophy of pool stores (and not a bad business concept really) is to have the customer put their faith in the pool store and be reliant on them to sell you what is needed. And then when you have "chlorine-lock", just drain 3/4 of the water and re-buy their chemicals to re-balance the water.

    I think it's great that you are curious, and that you found a great place to help you maintain your pool inexpensively and safely. Others may be able to lay out the Pool Store conundrum better than I.

    Feel free to continue to utilize the resources here and especially Pool School. Pool School. There is a graduation ceremony after you open your pool to clear water next spring!
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    Re: FC vs CYA Question

    Thanks guys for the responses!

    It is funny after reading your responses and thinking back to last time I went into the pool store after they tested my water. I starting asking the guy helping me about the pucks and CYA levels and how to prevent CYA levels from rising. He kinda nodded his head and said that basically you just have to drain some water to get CYA level back down. He quickly moved the conversation along to all the different chemicals I need based off the testing they performed and I politely told him I would take those into consideration and left. I am not saying he was deliberately trying to deceive etc, but it does seem like a very good business model to have customers completely rely on your testing and recommendations to keep their pool looking great.

    Anyway, I have a lot more to learn here and have already learned enough to feel fairly confident about maintaining my pool. I will hopefully get my TF-100 test kit in today or tomorrow and may post up some numbers just to get feedback from all the experts here!

    Thanks!
    22000gal IG plaster, Dallas, TX area (Feb 2016)
    Filter: Cartridge, Pentair
    Main pump: Pentair IntelliFlo VS (2HP)
    Boost pump: 3/4hp, Polaris cleaner

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    Mod Squad kimkats's Avatar
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    Re: FC vs CYA Question

    Easy answer for me! What he ^^^^^^^^^^^ said!

    I LOVE that you are asking questions! You will learn SO much and THEN be able to help others!

    How I learned what I did was reading a section at a time. You will see someone with a problem and all of the ideas and answers to get it fixed.

    Kim
    TFP Moderator 33x52 round AG 25,600 gals Sand Filter 1.5hp Pump - 2 Speed, SLAM, Pool School, Recommended Levels, Recommended Chemicals, Pool Math, Chlorine/CYA Chart, TF-100 Test Kit

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    Re: FC vs CYA Question

    I wonder if anyone has had any warranty issues keeping FC at higher levels?

    The pool guy my pool builder sent told me I was at risk at damaging my equipment when he tested my FC at 4 - referencing the "industry standard" 1-3. We all know this isn't true, but is totally what they teach in CPO.
    Helpful Links: Pool Chemistry 101 - Recommended Levels - Recommended Chemicals - FC/CYA Chart - SLAM Instructions - Pool Math
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    Re: FC vs CYA Question

    from what I've seen here, the whole cya/FC relationship goes back to one research paper from the 70's, in conjunction with a bunch of user observations. Major industry is probably not going to make a major change without more research and lab results, and if nobody is doing that research, the "old standard" ways just continue.
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    Re: FC vs CYA Question

    Quote Originally Posted by BuckeyeChris View Post
    from what I've seen here, the whole cya/FC relationship goes back to one research paper from the 70's, in conjunction with a bunch of user observations. Major industry is probably not going to make a major change without more research and lab results, and if nobody is doing that research, the "old standard" ways just continue.
    The strange part is that it isn't a major change. Its a 4ppm difference in recommended FC level at most.
    Helpful Links: Pool Chemistry 101 - Recommended Levels - Recommended Chemicals - FC/CYA Chart - SLAM Instructions - Pool Math
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    Re: FC vs CYA Question

    Quote Originally Posted by pinguy View Post
    I wonder if anyone has had any warranty issues keeping FC at higher levels?
    It is up to a pool owner to know the requirements for their warranty. There are some stories in the archives of owners being bound to certain ranges to keep their warranty valid, some even being required to submit occasional water samples to verify their compliance. Seeing how quickly some heaters have been destroyed by low pH I can understand the strictness of such requirements. In those cases the owner just has to work around it, by keeping their CYA low or other means of getting by with a low FC.

    I think BuckeyeChris has it, the standards are the standards and have been for something like 50 years. Most of the people in the industry don't follow the relationship not because they are afraid of losing money but because they don't even consider that they might be incorrect about something they have known their whole careers.
    JD - 28' Round Above Ground Pool, 17,000 Gallons. Dual speed Jacuzzi pump with cartridge filter. Dual speed 1 HP pump, Hayward S210T sand filter
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    Re: FC vs CYA Question

    This is an oldie but a goodie that covers this topic in some depth - blind faith and this forum?

    - - - Updated - - -

    Chem geek's Post #32 is particularly informative - blind faith and this forum? - Page 2
    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

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    Re: FC vs CYA Question

    Quote Originally Posted by JoyfulNoise View Post
    Chem geek's Post #32 is particularly informative - blind faith and this forum? - Page 2
    The EPA limits FC to 4ppm

    I suppose that sheds a bit of light on the 1-3 standard

    But it also begs the question...how are all these commercially run pools following 1-3 not having more issues with water quality? Low CYA and more frequent (several times per day) testing than a homeowner would do?
    Helpful Links: Pool Chemistry 101 - Recommended Levels - Recommended Chemicals - FC/CYA Chart - SLAM Instructions - Pool Math
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    Re: FC vs CYA Question

    Define 'Free Chlorine'. It is the chlorine that is not bound by CYA. So in most TFP pools it is much less then 4. More like 1 or less. Right?
    Bob - Palm Beach by San Juan Pools. approx 5000 gals., Pentair 320 cartridge filter (all new guts installed by me), Goldline SWG, 'New to me' Kreepy Krauly Sand Shark, Intermec 104 Timer Test kit: TF-100 w/Speed Stir

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    Re: FC vs CYA Question

    Quote Originally Posted by pabeader View Post
    Define 'Free Chlorine'. It is the chlorine that is not bound by CYA. So in most TFP pools it is much less then 4. More like 1 or less. Right?
    I'd think so, but how would one test for only unbound chlorine?
    Helpful Links: Pool Chemistry 101 - Recommended Levels - Recommended Chemicals - FC/CYA Chart - SLAM Instructions - Pool Math
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    JoyfulNoise's Avatar
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    FC vs CYA Question

    FC is defined as the sum of active chlorine (HOCl/OCl-) and chlorinated cyanurate (chlorine bound to CYA). That is what the test measures and that is what the industry defines FC as.
    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

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    Re: FC vs CYA Question

    you'd need to take your FC and do the math with your CYA. chem geeks old posts may have a table in them somewhere, but there's not a test for "Unbound" chlorine.

    Outdoor commercial pools have a much higher demand and have more robust chlorination methods, in addition to other sanitizing methods that are overkill for a residential pool. They are required to test throughout the day. If you are testing a lot, and only using OTO tests, then I suppose it also makes sense to have your FC target in the 1-4 range so you can use that test.
    10,500 gal IG, Topaz Pebble, auto-level
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    Re: FC vs CYA Question

    Quote Originally Posted by BuckeyeChris View Post
    you'd need to take your FC and do the math with your CYA. chem geeks old posts may have a table in them somewhere, but there's not a test for "Unbound" chlorine.

    Outdoor commercial pools have a much higher demand and have more robust chlorination methods, in addition to other sanitizing methods that are overkill for a residential pool. They are required to test throughout the day. If you are testing a lot, and only using OTO tests, then I suppose it also makes sense to have your FC target in the 1-4 range so you can use that test.
    But that calculation is based off the science the pool industry is not accepting, which lands us back at square one.

    Quote Originally Posted by JoyfulNoise View Post
    FC is defined as the sum of active chlorine (HOCl/OCl-) and chlorinated cyanurate (chlorine bound to CYA). That is what the test measures and that is what the industry defines FC as.
    Literally by that definition, it's impossible to recommended a FC level without knowing CYA. Madness.
    Helpful Links: Pool Chemistry 101 - Recommended Levels - Recommended Chemicals - FC/CYA Chart - SLAM Instructions - Pool Math
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    Mod Squad pooldv's Avatar
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    Re: FC vs CYA Question

    Quote Originally Posted by pinguy View Post

    Literally by that definition, it's impossible to recommended a FC level without knowing CYA. Madness.
    Agreed. Ask anyone here what level to set your FC and we will always ask what your CYA level is and show you the Chlorine CYA Chart
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