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Thread: Do I need to shock?

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    Do I need to shock?

    New to the forum and could use a little help. It's been very liberating so far to no longer feel entirely dependent on the pool store and their sometimes questionable and inconsistent advice on water treatment. After buying a good test kit of my own and reading the basics on this forum, I was able to balance my water virtually overnight where I had been going back and forth with bad results using the pool store's advice. Anyway.........

    My current readings are as follows:

    FC = 2.4
    CC = 0.4
    TA = 70
    pH = 7.5
    CYA = 70
    CH = 190

    I just converted to a SWG this season. Once I finally got the stabilizer down to 70ppm and the salt at 3200ppm, I added three 96oz jugs of bleach as the Pool Calculator suggested. This brought my FC up to right at 5 and CC at 0.2-0.3 as of yesterday morning. I have the SWG set at 50%. We had some rain come through last night - I checked the water again this morning around 9am and the FC had dropped to 2.6 but the CC was still around 0.3-0.4ppm. I checked it again this afternoon around 4pm and it had dropped to 2.4 with the CC still at 0.4ppm. Is this consumption just due to the rainfall or do I just need to turn up the SWG? It is a cloudy day with temps only around 70deg.

    Do I need to shock the pool?

    Do I need to increase the SWG output?

    If shocking is a good idea, I would like to clarify the super chlorinating shock method used on here - I just add the required amount of bleach to bring it up to 28ppm and keep it there checking the CC every hour or so until it drops to 0 then let the FC drop back down to normal levels? How long will it take the FC to drop back to below 5ppm?

    Sorry for all the questions but I want to be sure I know what I'm doing here. Thanks for the awesome information on this forum!
    In-ground, vinyl pool, 26,000 gals
    Hayward Sand Filter, Aquarite SWG, Hayward Ecostar Pump

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    Re: Do I need to shock?

    What does your water look like? A cc test result of .4ppm is the same as zero and no reason to shock.

    Unless you are having water quality issues, all you have to do is maintain your FC a little higher (3-5ppm) and you are all set.

    Your definition of shock is a little off but I don't think you need to shock to begin with.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Ohm_Boy's Avatar
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    Re: Do I need to shock?

    The trick is to find out how much FC you are losing overnight, when there is no sunlight/UV on the pool. You'll have to switch off the SWG, and take FC readings both in the evening and morning, and compare the two. Any loss then means that you have organics in your water. To overcome these organic nasties, you need to raise your FC to shock levels and maintain it there until there is no loss overnight.

    Once the FC holds overnight, and your CC is <1, and your water is sparkly, you can let the FC drop to normal, which it will do through UV loss to sunlight during the day.

    If your FC holds overnight, and your water is clear, then you have nothing to do but adjust the FC a little.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

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    Re: Do I need to shock?

    Why did my FC drop from 5 to 2.4 in a 24hour period? Was it due to the rainfall?

    Water is crystal clear.

    My SWG is set at 50% - does it need to be turned up to maintain higher FC? It's been rather cool here the past few days with temps only in the 70s.
    In-ground, vinyl pool, 26,000 gals
    Hayward Sand Filter, Aquarite SWG, Hayward Ecostar Pump

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    Re: Do I need to shock?

    Why did my FC drop from 5 to 2.4 in a 24hour period? Was it due to the rainfall?
    I don't know but it could be one of perhaps fifty things.

    Take the advice from ohm_boy and perform the OCLT. There are more directions in Pool School but he describes the process very clearly.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Do I need to shock?

    OK - did the overnight test. Added some bleach to get the FC up and shut the SWG off with pump still running.

    8:45pm FC = 5.2 / CC = 0.4

    6:30am FC = 3.6 / CC = 0.6

    So I need to shock. The only other thing that seems strange is my CYA dropped from 70ppm 2 days ago to 50ppm this morning. Should I add stabilizer at the same time I shock or wait until after?

    When I do shock, should I leave the SWG on at 100% and keep maintaining it at shock level with bleach until it passes the overnight FC loss test? Water looks fine right now but obviously something is off.
    In-ground, vinyl pool, 26,000 gals
    Hayward Sand Filter, Aquarite SWG, Hayward Ecostar Pump

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    Re: Do I need to shock?

    You will have much better success in your calculations during the shock process if you leave the SWG off. Additionally, running it at 100% shortens the cell life. Despite that all the manufacturers put some "super-chlorinate" mode on the SWG's, they simply are not good at it. Leave it off.

    Leave the Stabilizer alone until you finish the chock process.

    I'll bet you pass the OCLT around your 1st or second day...you were pretty close last night. Good work!
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Do I need to shock?

    Would it be easier to shock with some dichlor to help get the stabilizer up at the same time or just stick to the bleach?

    When shocking, should I just check it every couple of hours and add as needed to maintain the shock level until it passes the OCLT?

    Sorry for all the newbie questions.

    Thanks for the help!
    In-ground, vinyl pool, 26,000 gals
    Hayward Sand Filter, Aquarite SWG, Hayward Ecostar Pump

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    Ohm_Boy's Avatar
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    Re: Do I need to shock?

    My recommendation would be to not try to do two things at once. Use bleach and focus on the shocking process. Once your shock process is complete, then target the other parameters. Your life will be simpler for it.
    [center:1kpalu48]Helpful Links: Pool School | CYA/Chlorine Chart | Pool Calculator[/center:1kpalu48]

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    Re: Do I need to shock?

    Once I get it raised to shock level (25ppm) and it passes the overnight test, how long will it take for the FC level to drop back down to 5ppm or so?
    In-ground, vinyl pool, 26,000 gals
    Hayward Sand Filter, Aquarite SWG, Hayward Ecostar Pump

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    Re: Do I need to shock?

    Quote Originally Posted by Bent6
    Once I get it raised to shock level (25ppm) and it passes the overnight test, how long will it take for the FC level to drop back down to 5ppm or so?
    Just a heads up, plan on the shocking process to take a few days (you may get lucky and it doesn't, but don't plan on it). It is hard for us to predict how fast your FC will drop, since your pool's usage of chlorine will be different from other pools due to sunlight, temp, swimmer load, organic load, etc. If I was going to guess for my pool, and this is just a guess, it would take ~5 days. This most likely will not be the same for you.

    Focus on the shocking process for now!

    Quote Originally Posted by Bent6
    The only other thing that seems strange is my CYA dropped from 70ppm 2 days ago to 50ppm this morning. Should I add stabilizer at the same time I shock or wait until after?
    Did you do both of these tests? If yes, what test kit did you use? CYA does not just disappear, at least not quickly. Have you had a lot rain with spillover?
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Do I need to shock?

    Quote Originally Posted by linen
    Did you do both of these tests? If yes, what test kit did you use? CYA does not just disappear, at least not quickly. Have you had a lot rain with spillover?
    Yes. I am using a Taylor K-2006 test kit. My initial CYA test was 70ppm on Friday morning. We did get a big rainfall but no overspill. The CYA was 50ppm this morning. I guess it's possible I did it wrong the first time and maybe I didn't have as much CYA as I thought. Is the reading supposed to be just as the black dot starts to disappear from view or when it completely disappears?

    As far as the shocking process goes, I assume I should plan to test it every few hours and keep adding bleach as necessary to keep it at shock level until it passes OCLT?
    In-ground, vinyl pool, 26,000 gals
    Hayward Sand Filter, Aquarite SWG, Hayward Ecostar Pump

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    Re: Do I need to shock?

    Quote Originally Posted by Bent6
    Is the reading supposed to be just as the black dot starts to disappear from view or when it completely disappears?
    Totally disappears while full sun is at your back and test tube is at waste level.

    Take a look at the extended test kit directions. There is a link there that you can follow to see a picture of what you are looking for.

    Quote Originally Posted by Bent6
    As far as the shocking process goes, I assume I should plan to test it every few hours and keep adding bleach as necessary to keep it at shock level until it passes OCLT?
    Yes, that approach is best, you can shoot over shock level a little ways in order to always remain above it.
    TFP Expert who uses Pool School and my TF100 test kit along with PoolMath for my: Round 11K gallon AGP with deep end, 20" sand filter, Matrix 1hp 2spd, 6 2ftX20ft solar panels (and solar cover!), Intex SWCG (copper bars disconnected) and a Rubadub hot tub (chlorine). The SLAM process is not finished until: 1. CC < 0.5 ppm, 2. An OCLT < 1.0 ppm and, 3. The water is crystal clear.

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    Re: Do I need to shock?

    OK - think I've got it now. As stated above, yesterday morning after my first OCLT, it looked like I needed to shock as the FC had apparently dropped from 5.2 to what I though was 3.6. I was ready to shock but decided to test the water one more time yesterday afternoon after the SWG had run all day at 65%. FC had come back up to 5.0 with CC at 0.5. I decided to do another OCLT last night. Rechecked it this morning and the FC was a at 4.0 with the CC at 0.5. Hmmm - The only thing I can come up with to explain this is that I may have been having my finger in the water sample cup as I was scooping it out. Evidently the oil from my skin must have caused it to be off? The CYA is 50ppm so my initial reading of 70ppm must have just been my inexperience using the test. I'll add some stabilizer later this week.

    I turned the SWG down to 52% this morning. Rechecked this afternoon and the FC was back up to 5.5 with the CC now at 0. I turned the SWG down to 40% and I'll see what it looks like tomorrow. My wife thinks I'm obsessed with the pool and like some sort of mad scientist out there testing the water with my new test kit. At least I know it's right now!

    Here are my current levels......

    FC 5.0
    CC 0 - 0.2
    pH 7.5
    TA 70
    CH 180
    CYA 50

    I assume I'm in the clear now?
    In-ground, vinyl pool, 26,000 gals
    Hayward Sand Filter, Aquarite SWG, Hayward Ecostar Pump

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    JasonLion's Avatar
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    Re: Do I need to shock?

    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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