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Thread: how often to shock pool and FC amount

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    how often to shock pool and FC amount

    I'm new and going to shock my pool for the first time this weekend...I've used my Taylor K-2006 and taken the readings, used the FC/CYA chart for the correct FC level for shocking with the CYA I have, lowered the pH to 7.4 and used the Pool Calculator to determine that I need to raise the FC to 24 to shock my pool correctly and read in Pool School and some postings on shocking the pool including to shock the pool just as the sun goes down.....with that in mind, after I shock the pool and let it get back down to a FC of 7 for my CYA of 60 in my pool, my questions are two fold.

    First, The posts I've read are somewhat confusing to me, therefore this question. How often should I really need to shock the pool, knowing that I need to take into consideration rain fall which we have more than our share in Florida, and no one really uses my pool very often, if even at all. The pool store says weekly, but I know that isn't the correct answer........

    Secondly, I have my grandchildren coming early this summer to visit, and they are all under 7 years old....I'm concerened that a FC of 7 that I should keep with my CYA reading might be too high for them based on their tender skin at their ages. So since I can't get the CYA down to get a corresponding lower optium FC reading, is it OK, to just lower the FC down while they are here, then shock the pool and then target to get the FC back up to the 7 level after they leave?.....not for sure what I should do

    I would appreciate any insights that anyone with experiences in the above two areas might have that would be of help...this website has been a life saver for me since my pool guy did me a big favor and walked off the job, I never realized how much he was taking advantage of me until I began to try to learn how to do my pool myself.......many thanks, John
    16100 gallon rectangle pool built in 1984 including a 5' X 5'x 3' Spa, Diamond Brite in year 2000, Non-SWG Pool

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    Join Date
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    Re: how often to shock pool and FC amount

    Shocking is a process where you keep your FC at shock level, testing very frequently and adding bleach to keep it there until you pass the 3 criteria described in "shocking your pool" in pool school. It's not "bring to shock level and leave it alone to go down on it's own".

    A FC of 7 is not "high" for you level of CYA, it's normal and absolutely necessary. The chlorine is "bound" to the CYA so the effect on anything even the kids is kept the same following the CYA/chlorine chart. If you drop below it you invite baddies to grow which would be worse for the kids and everybody.

    As to the question of "how often should you shock your pool"? The ONLY TIME you need to go through the shock process is if you have a problem with your water or you expect or experience an unusual event will cause you trouble, it's not something we do "just because". If you maintain your FC level above the min for your CYA you shouldn't have to ever shock your pool except maybe at opening and closing. That's the whole point of keeping your FC in range and never drop below min as it prevents "problems" and has adequate sanitation to effectively stop anything from growing in the pool.

    ps - I hope you realize your CYA is on the high side for a non-SWG pool. You can manage with it but realize it will take more bleach to shock. You can lower it by vacuuming to waste and over time it will go down as you replace water. Just make sure you never use any product that has CYA in it like dichlor or trichlor.
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

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    thehowheels's Avatar
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    Re: how often to shock pool and FC amount

    Hi lawjohn,

    You should shock if:
    * you have algae
    * your combined chlorine (CC) is higher than 0.5
    * your FC is 0

    There's absolutely no reason to shock once a week, but I know many pool stores advise their customers to do so. A very expensive strategy!

    See The Shock Process in Pool School for detailed information

    Second, an FC of 7, with a CYA of 60 is perfectly safe, even for small children. If you look at the Chlorine / CYA Chart, you'll see an FC of 7 @ 60 CYA is equivelent to 3 FC @ 20 CYA. Conversely, if you had 3 FC with zero CYA, the chlorine would likely eat right through the elastic of your swimwear!
    Matt
    9k gallon, plaster, IG. Raised spa w/ spillover into pool. AO Smith Century Centurion / Purex Triton WisperFlo 0.5 HP, Hayward 1.5 HP (spa), Polaris 1-516-01 1.5 HP (blower). Hayward DE3620 36 ft2 72 GPM DE Filter, Polaris 145 cleaner. Pool built ~1980.
    Trouble-free, BBB since: April 25, 2013

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    Isaac-1's Avatar
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    Re: how often to shock pool and FC amount

    I agree, shocking should only be done when needed, not every so often, think of it as like patching a tire on a car, how often should you do it, well probably when you have a flat (major algae bloom), or when you have a small leak (small algae bloom)...

    p.s. lowering your FC level while the kids are there is more likely to make the water so it will irritate them, I know this seams backwards, but it is true, under chlorination causes CC (combined chlorine) to build up, that is the "chlorine smell" that most people talk about so often associated with burning eyes, etc.
    Indoor 20x40 35,000 gallon vinyl pool with 1.5 HP 2 speed Jandy FloPro pump, Hayward EC75 Perflex DE filter, 11 4x12 Techno-Solis solar panels w/ Aquasolar controller, Aquabot Turbo T Robot Cleaner. Also LMI metering chlorine dispenser pump and HotSpring Jetsetter
    I use and endorse TFtestKits TF-100 from http://tftestkits.net
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    Join Date
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    Re: how often to shock pool and FC amount

    I missed the obvious question - why are you shocking your pool? Can we get a full set of test results?
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

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    duraleigh's Avatar
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    Re: how often to shock pool and FC amount

    I will repeat what has been said above just for emphasis. You will not "shock" your pool with a single dose of chlorine. It is a process that can take several days and will require multiple doses of chlorine. Reread the article in Pool School.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: how often to shock pool and FC amount

    This is my 3rd year with my pool and the next time I shock my pool will be the first. On a related note, I've got an entire tub of dichlor that my father in law got me our first year if anybody wants it.
    29,000 gallon, concrete pool and spa, SE PA
    Jandy 2HP pump, Raypak 400 heater, Polaris 380

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    frustratedpoolmom's Avatar
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    Re: how often to shock pool and FC amount

    I've shocked my pool for 2 reasons - extended vacations of more than 3 days, winterization. Other than that I haven't shocked my pool more than twice a year since 2007.
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
    150 Sq ft. Clearwater Cartridge Filter; Former and DISSATISFIED "Pool Frog" owner
    http://www.PerfectlyClearPoolService.com

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    Re: how often to shock pool and FC amount

    Wow, don't know what happened to my answer, so here goes again...the reason for shocking is I found a small amount of algae when the pool guy quit..want to get to it before it gets out of hand...now for my numbers:

    FC 8.5
    CC.5
    pH 7.4
    TA 100
    CH 290
    CYA 60
    John
    16100 gallon rectangle pool built in 1984 including a 5' X 5'x 3' Spa, Diamond Brite in year 2000, Non-SWG Pool

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    Join Date
    Jun 2012
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    Re: how often to shock pool and FC amount

    Visible algae and presence of CC means you should indeed go through the shock process. If it's small it will only take 3-4 days to pass the 3 criteria to be done shocking if not less. Keep at it and:

    NIP IT IN THE BUD!

    From there on out you MUST maintain your FC levels based on your CYA according to the chart. Minimum means minimum, never let it get below that or you may find yourself having to go through shocking again. The purpose of keeping FC at proper levels is so you don't have to "shock".

    One of the biggest aspects of a troublefree pool is constantly maintaining your FC for your given CYA. It is the utmost important aspect to troublefree. If you don't do that, it won't be troublefree and you'll fall into the yo-yo effect of dumping "shock" chemicals every week or so that pool store recommends.

    -off topic-
    Friends with pools come over and say how nice my pool looks. "I guess you shock it weekly right? You dump 'shock' in there every week or something? You must spend a lot of time taking care of that pool?" they say. I just point them here.

    Trouble free is trouble free.
    18x36 inground vinyl lined, Hayward sand filter and tablet chrolinator, approx 18k gallon

  11. Back To Top    #11

    Re: how often to shock pool and FC amount

    I want to thank everyone for taking the time to provide the very helpful guidance ....it's very much appreciated.....thanks, John
    16100 gallon rectangle pool built in 1984 including a 5' X 5'x 3' Spa, Diamond Brite in year 2000, Non-SWG Pool

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    Re: how often to shock pool and FC amount

    spidey07 again many thanks,,,,my next door neighbors on both sides of my house have problems with their pools also and I too have pointed them to this site.....Hopefully they will take advantage of the opportunity also....thanks again, John
    16100 gallon rectangle pool built in 1984 including a 5' X 5'x 3' Spa, Diamond Brite in year 2000, Non-SWG Pool

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