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Thread: How high an FC would you consider 'swimmable' (with high CY?

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    Join Date
    Aug 2009
    SF Bay Area (Lamorinda), CA

    How high an FC would you consider 'swimmable' (with high CY?

    As some of you already know from my CYA thread, I've been trying to keep my FC levels at around 7-12 while I try to slowly replace water to lower CYA (120 ppm) and keep the mustard algae at bay. Currently my FC is reading 10.5 (to get an idea of how my FC has been trending, it was 10.5 at 6 p.m. last night and then it was 6ppm at 7:30 this morning.

    Also on an unrelated note, I still have phosphate reducers (PhosFree and Pool Perfect + PhosFree) that were purchased during my "unenlightened" days prior to joining TFP - would it be useful to add these to help keep algae at bay or would it more likely mess with my water? Our pool does tend to run on the high side as far as phosphates go (according to the pool store results anyway, which I understand are not always the most accurate
    1950's-era 17K gallon formerly fiberglass, newly replastered IG rectangle (~15x30'),
    Hayward S244S Sand Filter with Franklin Electric 0.75 HP motor and WhisperFlo WFE-3 pump
    Clear ThermaTex bubble cover
    Manual vacuum

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    TravisD's Avatar
    Join Date
    Jul 2009
    Tampa, FL

    Re: How high an FC would you consider 'swimmable' (with high CY?

    As I understand it, as long as you keep your FC level at your target level in relation to your CYA level, algae will not grow and phosphate levels will not even matter. Phosphates feed algae, but if algae isn't present, then phosphate levels don't matter.
    If your CYA is 120 then I think you should keep your FC higher than 12. 12 is for a CYA of 100. I'd go a few ppm higher. I'm not sure on the exact number as it is off the CYA/FC chart in pool school.
    You can safely swim all the way to shock level. You are well below that.
    Keep your FC levels where they need to be and you won't have to worry about algae.
    24' Round AGP | 13,600 Gallons | Waterway Cartridge Filter | Waterway 2 Speed Pump | K-2006 Test Kit
    100% Trouble Free Since The Baqua Conversion

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    JasonLion's Avatar
    Join Date
    May 2007
    Silver Spring, MD

    Re: How high an FC would you consider 'swimmable' (with high CY?

    Trying to remove phosphates, starting with a very high phosphate level, will almost always cloud up the water quite badly. It will clear eventually, but since removing phosphates is almost never all that important, why go through that trouble.
    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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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: How high an FC would you consider 'swimmable' (with high CY?


    I know you didn't ask, but you have algae in your pool. A 4.5 drop in your FC overnite indicates you need to shock the pool to rid it of the organics that are causing that drop.

    Phosphates are irrelevant but you are consuming a ton (relative to what you would normally be consuming) of chlorine in your pool and will continue to do so until you get rid of the algae.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  5. Back To Top    #5

    Re: How high an FC would you consider 'swimmable' (with high CY?

    To answer your original question (in your subject line) most here would not hesitate to swim in FC levels up to the shock level for your CYA. Wear an old suit, just in case, and rinse upon exiting the pool.

    I would probably not allow a baby or dog or others who don't understand not to drink the pool with FC that high.

    8000 gallon 20' x 48" round vinyl frame pool, 12" sand filter (don't have the specs on the pump), TF100 test kit
    Handy Links: PoolMath, TF-100 Test Kit, Pool School, CYA-Chlorine Chart
    "Shock" is a process, not a product!

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