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Thread: All good but low FC

  1. Back To Top    #1

    Join Date
    May 2010
    Dallas TX

    All good but low FC

    Excuse the long post - I've tried to add all the relevant info

    My new (to me) pool seems to like low FC for some reason. I bought the place Oct '09, so this is the first season I've been managing the pool.

    33k gallons gunite
    Clearwater SWG
    DIY acid dosing system
    DE filter
    Salt 3200ppm
    pH 7.5
    FC 1
    Temp 90F
    CC 0
    Borates 50ppm
    Ch 420
    TA 80
    CYA 100
    no overnight CL loss

    Only thing that jumps out is low FC. It's been cruising at 1ppm since the pool opened in March. Water has been around 90F for a month. I'd expect to see issues by now if it was going to happen.

    No algea, no scum, no smell, nothing. Water is gorgeous.

    Once I shocked it up to 40ppm . It slowly stabilized right back to 1ppm.

    Once I kept it at 10ppm for a week using bleach, according to the CYA/FC chart. The pool smelled like CL and stung our eyes. So I let it go back down.

    Pump & cell run 6hrs a day, right at about 1 turnover. Cell setting is 100% output. Cell is the 24k model, a bit undersized. Cell seems to make lots of CL in the bucket test.

    Once the pump lost prime and did not pump for 2 days (poor gasket seal). Water turned slightly cloudy, cleared back up in 6hrs of running. This tells me the pool is pretty dang stable , nothing going on.

    Numbers are from the 'big' test kit. The FC readings from the various tests, strips, and pool store are consistant.

    Such low FC numbers have been bothering me all season, but I'm tempted to shrug and accept it .

    Any thoughts?
    33k Gunite, CompuPool CPSC48 SWG, Sta-Rite System 3 DE, 2.25hp dual-speed, POOLVERGNUEGEN Pressure-side

  2. Back To Top    #2
    Mod Squad Bama Rambler's Avatar
    Join Date
    Jun 2009
    SouthWest Alabama

    Re: All good but low FC

    You already hit on the answer. "Cell is the 24k model, a bit undersized" There's your problem right there. It's almost 30% too small. And only running 6 hours a day. No wonder you're not making enough chlorine.
    Dave J. TFP Moderator
    24' x 52" Round AGP. 2hp/¼hp SPL Power-Flo 2-speed pump. 200sqft Waterway Cartridge Filter. 45MHP2(3GPD) Stenner Peristaltic Pump
    Pool School ----- Pool Math ----- TF-Test Kit

  3. Back To Top    #3
    Melt In The Sun's Avatar
    Join Date
    Oct 2009
    Tucson, AZ

    Re: All good but low FC

    To build on what Bama said, more pump run time will help get your FC up. It needs to be higher; you've been lucky so far, but I wouldn't push it.

    If you got a strong chlorine smell and stinging eyes at 10 ppm FC and 100 ppm CYA, something else was wrong. That level will not sting eyes.
    11,200 gal, Pebble-Tec; Tristar 2-speed 1hp - Swimclear 325 ft2 cart - SWG - A & A in-floor cleaner - Heat pump. For the poolside cooking, a Yoder Wichita and a Big Steel Keg!
    TF Test Kits -- PoolMath -- Pool School
    Make each day your masterpiece. - John Wooden

  4. Back To Top    #4

    In the Industry

    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: All good but low FC

    Any thoughts?
    It appears to me you have managed your pool quite well despite being outside normal parameters. I think you're cutting it too close on FC.

    If it were my pool, I would never allow the FC to dip below 3-4ppm. With the slightest slipup in your management, you can get an algae bloom that will take you a ton, A TON, of chlorine to clear up because of your CYA being so high.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  5. Back To Top    #5

    Join Date
    May 2010
    Dallas TX

    Re: All good but low FC

    hmmm thanks for the input.
    I'm kinda unwilling to increase the pump runtime to generate more FC, spinning that big motor is spendy. 6hrs seems to be the sweet spot for keeping the water looking good, and running the vacuum enough to clear small debris.

    Would suppliment with Bleach to 4ppm be OK? I could probably rig an auto-doser in addition to the acid doser. Once the cell dies, a bigger one can drop right in, correct?

    Melt In The Sun: the CL smell & sting was noticeable but not terrible. I guess we're spoiled.
    33k Gunite, CompuPool CPSC48 SWG, Sta-Rite System 3 DE, 2.25hp dual-speed, POOLVERGNUEGEN Pressure-side

  6. Back To Top    #6
    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: All good but low FC

    Sure, as long as you maintain the correct levels it doesn't really matter how you do it.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
    Creator of PoolMath and Pool Calculator. Other handy links: Support this site, TF Test Kits, Pool School

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