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Thread: How high can CYA go?

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    Join Date
    Jul 2016
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    Question How high can CYA go?

    I normally use bleach to chlorinate my pool, but will occasionally use my in-line chlorinator with tri-chlor tabs, only when I am going to be away for a week or more. So my CYA level will go up only when I am away, typically about 7 PPM for each week that I have to use the chlorinator. I don't use algaecide, and don't have any algae in the pool.


    My CYA level is currently about 65. I am keeping my minimum FC level at or above the levels shown in the Chlorine/CYA chart, so as my CYA slowly goes up over time, I raise the minimum FC level as well (I use the FAS-DPD test).


    I find that using higher FC levels does not require me to use more chlorine since I only have to replace what is lost each day due to the sun. So, it is not more costly to keep my pool at a higher FC level.


    The chart says that for CYA=100, the minimum FC level should be 7, and the target FC level should be 12. The shock FC level would be 39, but if I keep on top of things, I shouldn't need to shock it. The footnote in the chart says that CYA levels of 70 or above are not recommended, even though the chart goes all the way up to CYA=100.


    So I'm wondering what is really the practical limit to which I can go on my CYA level, before I have to drain the pool? At some point the required FC levels would probably start to become damaging to the equipment, perhaps?
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit

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    Mod Squad jblizzle's Avatar
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    Re: How high can CYA go?

    Really, you can maintain the CYA as high as you want, it is really when a problem develops and a SLAM is necessary that the high CYA becomes a problem because the FC is then very high. However, keeping the FC and CYA in balance to each other will not become damaging to the equipment.

    The other issue is that when the FC > 10ppm, the pH test starts to read incorrectly high. So, if you have to keep the FC above 10ppm due to high CYA, you never are really able to keep an eye on the pH.
    Jason, TFP Moderator
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  3. Back To Top    #3

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    Re: How high can CYA go?

    Thanks.
    If I extrapolate the chart, it looks like if I went as high as CYA 150, my minimum and target FC levels would be 10.5 and 18. At that point I'd probably not want to go any higher, based on pH test problems, etc. It will probably take a couple years before I have used the chlorinator enough to reach those levels, and by that time it would probably be best to drain the pool and start over.

    I think the in-line chlorinator is a nice backup to my regular bleach dosing, if used infrequently, and the CYA is monitored. I can't believe I used to use it all the time however. Ignorance is not bliss, when it comes to pool maintenance.
    16,000 gallon outdoor in-ground 16'x32' plaster pool (built 2002); Pentair Intelliflo VF pump; Jandy Cartridge filter;Rainbow in-line chlorinator (used only when I am away); Hayward 2 wheel suction-side pool cleaner; LARS gas heater, Taylor K-2006 FAS-DPD test kit

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    Mod Squad tim5055's Avatar
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    Re: How high can CYA go?

    I,guess the question is how many week long trips are you yptaking a year? If it only vacations then two or three? Now, if you travel for work that is a different story.

    If it's,only vacations,,then what's yiurmCYA going,to,go up in a year? 30 ppm maybe? You could,easily loose that in a year just with natural degradation of the CYA (figure 1ppm per month) and splash out if you use the pool a lot.

    Now, if you travel regularly for work and this is going to happen often, I would suggest looking into a SWCG or Stenner Pump to keep away from the pucks.

    Here is the original FC/CYA chart before it was made pretty for Pool School. Chlorine/CYA Chart

    At the bottom in the notes you will,see that the minimum FC should,be is 7.5% of CYA

    But, you are showing that knowledge is power. Keep the FC/CYA ratio correct and life should be good.
    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

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