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Thread: FC between 1 and 3 ppm seems to be the norm

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    FC between 1 and 3 ppm seems to be the norm

    FC between 1 and 3 ppm seems to be the norm outside this forum.

    I'm just wondering why we recommend higher levels.

    Rick
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    Re: FC between 1 and 3 ppm seems to be the norm

    Maybe they want to sell you all that algae type stuff. I really think it's because most places don't understand the CYA/FC relationship.
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    JasonLion's Avatar
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    Re: FC between 1 and 3 ppm seems to be the norm

    The FC between 1 and 3 rule dates back to before the introduction of CYA. If you are not using CYA it is a very appropriate recommendation. However, once there is CYA in the water everything changes significantly. CYA binds to most of the chlorine, dramatically reducing it's effective strength. You need to raise the FC level to compensate for this or your pool will not be kept sanitary.
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    Re: FC between 1 and 3 ppm seems to be the norm

    Quote Originally Posted by JasonLion
    The FC between 1 and 3 rule dates back to before the introduction of CYA. If you are not using CYA it is a very appropriate recommendation. However, once there is CYA in the water everything changes significantly. CYA binds to most of the chlorine, dramatically reducing it's effective strength. You need to raise the FC level to compensate for this or your pool will not be kept sanitary.
    Thanks. That's interesting. Is this accepted fact among the experts and just the lay people are confused, or are the experts in disagreement on this as well?

    Rick
    24' Round AG Vinyl Pool (13,500 Gallons)
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    Re: FC between 1 and 3 ppm seems to be the norm

    Rick,

    What experts do you mean? There are quite a few people on this forum (not me) that are as "expert" as anyone else in the world. I don't know a better resource anywhere (or frankly, as good) to get the advice you need to manage your pool.
    Dave S.
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    Re: FC between 1 and 3 ppm seems to be the norm

    Check out ChemGeek's posts in The Deep End ... recent discussions on this very topic.

    Posted with Tapatalk ... sorry if I sound short ... hate typing on phone
    Jason, TFP Moderator
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    Re: FC between 1 and 3 ppm seems to be the norm

    The issue you are having is totally understandable. How can the standard recommendations of seemingly all pool chemical and equipment manufacturers be incorrect? I struggled with this as well - it makes no sense.

    However if you go through the more scientific posts on this site from Chemgeek and others you will find a detailed technical analysis that no one else has compiled. In addition to that consider the following :

    1) 1-3ppm FC is based off EPA drinking water recommendations (No CYA present) - from a liability point of view this is a very easy road to take
    2) All forms of solid chlorine contain by-products that build up over time (CYA or Calcium). This is a very inconvenient fact of life that no manufacturer talks about
    3) Until the internet there was no way to compile the collective experiences of thousands of pool owner/operators
    4) The low FC recommendations also include some sort of weekly "shock" treatment and periodic water replacement. The shock treatments are to kill off the algae that is ever present in a low FC pool, the water replacement to fix the inevitable rise of cya that makes the chlorine increasingly less effective.
    5) There are plenty of common pool store ideas that a patently false on their face - Chlorine "Lock" and standard TDS advice come to mind

    Once you put all that together you find a pool service industry that gives rather poor advice (overall) - and has absolutely no economic reason to change. However unlikely that seems at first.
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    Re: FC between 1 and 3 ppm seems to be the norm

    The science to show what is happening was done in the 1970s and 1980s, and is not contested, but the pool industry has been very slow to respond. The pool industry is very conservative and simply continues to do/recommend what they have always done/recommended. There is way more detail in this post.
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    Re: FC between 1 and 3 ppm seems to be the norm

    Thanks, I read through the deep end part and saw a lot of good empirical data supporting this approach. I appreciate that.

    One part I didn't quite get (well, at least one).

    We use CYA to protect the FC but it forces us to use higher levels of FC since some is combined with the CYA and not available for sanitation. With an SWG that allows us to add FC all the time, why not use lower levels of CYA and less FC? It looked like you get significant benefits with even 20%.

    I think this was an attempt to explain it:
    Salt Water chlorine Generation (SWG) pools seem to require a higher level of CYA, about 70-80 ppm, to operate efficiently. The theory is that the CYA is slow to "store" the chlorine as it is being generated so without enough CYA there is a build-up of chlorine that degrades the performance of the salt cell. I would prefer that the SWG manufacturers offer a larger lower-power (per length) cell that would work efficiently at lower CYA concentrations.

    Rick
    24' Round AG Vinyl Pool (13,500 Gallons)
    Sand Filter, Aquabug Vacuum
    Pump Size: ?? Flow Rate:??
    Shifted from Baquacil to Chlorine 8/2011

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    Re: FC between 1 and 3 ppm seems to be the norm

    CYA is a bit of a balancing act, the more you use the less chlorine you need to use, but the more likely you are to have complications. For normal pools CYA at 30 to 50 is a good balance between the advantages and the disadvantages. Adding a SWG changes two factors that affect this tradeoff. First the SWG makes it much less likely you will need to shock the pool, significantly reducing the chances of complications due to high CYA. Secondly the SWG lifetime is very dependent on how much total chlorine you need. Higher CYA levels mean less chlorine used and thus a longer lifetime for the SWG. These two factors shift the balance so that higher CYA levels (70 - 80) work better with a SWG than they would without.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: FC between 1 and 3 ppm seems to be the norm

    Quote Originally Posted by JasonLion
    CYA is a bit of a balancing act, the more you use the less chlorine you need to use, but the more likely you are to have complications. For normal pools CYA at 30 to 50 is a good balance between the advantages and the disadvantages. Adding a SWG changes two factors that affect this tradeoff. First the SWG makes it much less likely you will need to shock the pool, significantly reducing the chances of complications due to high CYA. Secondly the SWG lifetime is very dependent on how much total chlorine you need. Higher CYA levels mean less chlorine used and thus a longer lifetime for the SWG. These two factors shift the balance so that higher CYA levels (70 - 80) work better with a SWG than they would without.
    Got it. Longer life for the cell because you don't need to produce as much chlorine. Thanks.
    Rick
    24' Round AG Vinyl Pool (13,500 Gallons)
    Sand Filter, Aquabug Vacuum
    Pump Size: ?? Flow Rate:??
    Shifted from Baquacil to Chlorine 8/2011

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