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Thread: Whats the highest FC level you can have and safely swim?

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    Whats the highest FC level you can have and safely swim?

    Im still trying to get rid of my algae. Water is clear but need a level of 35PPM to kill it.
    Any idea what a safe level would be? While Im asking,also curious what public pools keep
    there levels at. You can usually smell the chlorine a mile away. Thanks
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    Butterfly's Avatar
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    Re: Whats the highest FC level you can have and safely swim?

    You can swim up to shock level based on your CYA level.

    The smell from the public pools is chloramines. The cure for that is more chlorine. I don't know the requirements for public pools, but I have read that kiddie pools are kept pretty high - think diapers.
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    Re: Whats the highest FC level you can have and safely swim?

    So there is no set FC level,it depends on your CYA #. My CYA level was 90 and was told I need to maintain
    a shock level of 35 PPM. As long as my FC doesnt go above 35 Im safe to swim? By the way how was FC shock
    level determined to be 35PPM with my CYA at 90 PPM. Cant seem to compute it on the pool calculator..
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    Mod Squad Bama Rambler's Avatar
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    Re: Whats the highest FC level you can have and safely swim?

    That's correct, your FC level is relative to your CYA level.
    If you take a look at the Chlorine/CYA chart in pool school you'll see what your shock level should be.
    There's a little difference between the Pool Calc and the chart. Either wil work but the chart is a little more aggressive.
    It is safe to swim up to shock level.
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    Re: Whats the highest FC level you can have and safely swim?

    If you can smell the chlorine a mile away, chances are those public pools are keeping their chlorine level very low (too low). Contrary to popular belief, the distinct smell of chlorine in a pool is NOT indicative of over-chlorination (per se), but rather the existence of chloramines. It means you actually need MORE chlorine to combat the organics in your pool and to get rid of the chloramines.
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    Re: Whats the highest FC level you can have and safely swim?

    In high bather-load pools, such as many commercial/public pools, even having higher chlorine levels isn't enough to keep up with the bather load, especially in indoor pools where there is no sunlight (so no UV) to help break it down and the air circulation is often poor. In these situations, supplemental oxidation is helpful such as from UV or ozone systems or from use of non-chlorine shock (MPS) or enzymes. This isn't necessary in a residential outdoor pool since the bather-load is so much lower so chlorine is able to keep up.

    Also, in indoor pools, Cyanuric Acid (CYA) is often not used and this makes the active chlorine (hypochlorous acid) level higher by a factor of 10 or more. This can lead to much higher concentrations of volatile and very smelly and irritating nitrogen trichloride. It's a delicate balance -- if one uses too little chlorine in absolute (FC) terms so that it runs out, then one can end up with too much monochloramine which is associated with "pool smell" though not quite as irritating while if one doesn't use CYA then one can end up with too much nitrogen trichloride.
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    Re: Whats the highest FC level you can have and safely swim?

    We say that you can swim up to shock levels, but typically don't recommend swimming while actually shocking.
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