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Thread: What's the risk of 0FC for a day

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    What's the risk of 0FC for a day

    I run my pool with a CYA of 30 and keep the FC around 3 or so. On a day like today with heavy swimmer load and lots of sun, I will check the pool at 8AM and it will have 3 FC but by 4PM it's down to 0 FC.

    If I load back up the clorine to 4 - 5 FC, what's the best guess of running into a problem with algea? Wouldn't it would take more than a few hours of time before it would take root? I have no issues with the water, it's crystal clear and 80 degrees. Just curious what my risks would be as I've only shocked the pool once this year after a heavy rain storm. This situation of 0 FC happens maybe 1 a month.

    Based on these types of days, I'm thinking I will be boosting my CYA up into the 50-60 range to help buffer a little more.

    20,700 gal gunite/plaster ig pool w/ SWCG and DE filter near DFW TX

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    duraleigh's Avatar
    Join Date
    Apr 2007
    Sebring, Florida

    Re: What's the risk of 0FC for a day

    It sounds to me like you got good control over your pool water. My guess is you'll be fine in the scenario you describe with one exception to consider. The chlorine is in there not only to prevent algae but to kill bacteria and all sorts of organic unpleasantness that can get in pool water. If you've got a bunch of swimmers and no chlorine, you're pool is unprotected.

    Raising your CYA would work but I think you would use less chlorine if you simply put in some extra when you expect the pool to be active. A jug of clorox is pretty painless and would be quite helpful in keeping your pool sanitized.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Join Date
    Mar 2007
    San Rafael, CA USA
    Algae takes from 4 to 8 hours to reproduce, that is to double in population size (its "generation rate"). So one day of getting to zero chlorine will probably just start to make the water dull looking though that could take two days. The next day could be cloudy to getting green and the next day may be a full-on bloom. However, getting to zero chlorine will also allow bacteria to multiply and they reproduce much faster than algae, taking 15 minutes to an hour to double in population. So it's not a good idea to let the chlorine get to zero and would be better to see if higher CYA with higher FC kept the lowest FC level higher.

    I agree with duraleigh that if you know it's going to be an exceptionally hot sun-intense day with lots of bather load, you can add some more chlorine in the morning (or the previous night).

    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"

  4. Back To Top    #4
    Thanks guys, I'll keep in mind the bacteria and will raise the FC in the AM of those heavier use days.
    20,700 gal gunite/plaster ig pool w/ SWCG and DE filter near DFW TX

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