Become a TFP Supporter Pool Math Forum Rules Pool School
Results 1 to 5 of 5

Thread: Minimum FC 7.5% of CYA

  1. Back To Top    #1

    In the Industry

    Join Date
    Feb 2013
    Location
    Pool Country
    Posts
    138

    Minimum FC 7.5% of CYA

    Ok, so supposedly the minimum free chlorine should be 7.5% of cyanuric acid.

    http://www.lowrycg.com/wp-content/up...Pool-rev03.pdf

    Target free chlorine should be what percentage of cyanuric acid?

    I want a formula, not a chart.

  2. Back To Top    #2
    Mod Squad jblizzle's Avatar
    Join Date
    May 2010
    Location
    Tucson, AZ
    Posts
    37,389

    Re: Minimum FC 7.5% of CYA

    The target is high enough such that it does not drop below the minimum before the next time you are there to add more chlorine. There is no set %.

    Also realize that the minimum is 5% for SWG pools.
    Jason, TFP Moderator
    18k IG pebblesheen pool, Hayward ProLogic P4 w/ T-15 SWG, Pentair 1HP 2-speed Superflo, Hayward 6020 DE filter
    500 sqft Heliocol solar panels, ThePoolCleaner, TF-100 test kit w/ SpeedStir
    Pool School + Test Kit + PoolMath = A TROUBLE FREE POOL
    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

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

    Re: Minimum FC 7.5% of CYA

    Quote Originally Posted by 09659
    I want a formula, not a chart.
    That can only come from trial-and-error. There are too many variables affecting FC consumption to make an easy formula. UV varies considerably throughout the year and the latitude, and even if you get a lot of fog or clouds. Temperature affects it as well. So does usage - a pool that never holds any dirty bodies will use less than one that has dozens of children. And then there's the amount of organic debris that the chlorine tries to oxidize.
    Complicating things, the amount of chlorine degraded by UV is a percentage, not a fixed PPM. So there comes a point when overchlorinating becomes a waste, because you lose it faster as the FC level gets higher - which is also why you can't just add three days worth of bleach every third day.

    Test FC, keep records, and pay attention. You'll get a gut feeling for your pool's daily appetite quick enough.
    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

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

    Re: Minimum FC 7.5% of CYA

    Quote Originally Posted by 09659
    Ok, so supposedly the minimum free chlorine should be 7.5% of cyanuric acid.

    http://www.lowrycg.com/wp-content/up...Pool-rev03.pdf

    Target free chlorine should be what percentage of cyanuric acid?

    I want a formula, not a chart.
    By the way, just to be clear, a lot of the information in Bob Lowry's article you reference came from me as he took some of what I wrote on (mostly) this forum, modified and organized it along with adding some other material (such as charts he made on TA buffering using my Pool Equations spreadsheet), and had me review it. And of course, Ben Powell came up with the original Best Guess Swimming Pool Chlorine Chart that I used along with the chemistry of chlorine/CYA to come up with minimum FC/CYA ratios to inhibit algae growth (with a later modification at a somewhat lower level for SWG pools).

    As others have noted, the amount of chlorine you will need as a target depends on factors that you can't put into a single formula. It's just easiest to measure your 24-hour chlorine loss on a typical day and then just set your target at the minimum plus at least that drop assuming you add chlorine every day. Since you are in the industry, if you are a pool service then obviously this approach will not work for you since you may only visit pools once a week. We can discuss various options for you, but they are not the mainstream ones for this forum that focuses on residential pools maintained by their owners so such discussion should be moved to another area so as not to confuse newbies. This post discusses some typical options and we also discussed this in an earlier thread you participated in here.
    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"

  5. Back To Top    #5

    In the Industry

    Join Date
    Feb 2013
    Location
    Pool Country
    Posts
    138

    Re: Minimum FC 7.5% of CYA

    Thank you

Posting Permissions

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