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Thread: Need to Shock?

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    Need to Shock?

    So we had pool people for about 8 months after getting tired of the Leslies "buy a bunch of this and bring another sample so we can tell you what else to buy tomorrow" run-around. But they stopped showing up and after a few weeks I had a green pool. I changed the DE in my filter, threw in some Leslies Power Powder that I still had, vacuumed the bottom, and got a nice clean pool. But I knew I was going to have chemical troubles again, so after some googling I found The Pool Calculator and Trouble Free Pool. I'm convinced, and I've been working on reducing my TA with acid and using liquid chlorinator (first I used Clorox, but the 10% chlorine at Lowe's was cheaper at $6/2 gallons).

    Here are my numbers this morning:

    FC: 1
    pH: 7.4 (after taking it down to 7.0)
    TA: 150 (down from over 200)
    CYA: ~50 (I'm using an AquaCheck test strip for this since I don't have one of the recommended kits yet).

    I added chlorine to bring FC back up to 5, but it keeps dropping low after a day or two. I thought maybe the high TA or the low pH were causing the quick drops, but after re-reading the shock section in Pool School I think the problem is probably excess organics still in the pool (although the water looks beautiful) and that I need to shock the pool and keep it shocked until it holds steady. Does this sound correct?

    I'm guessing the nasty stuff is stuck in the filter, so would it be better to change my DE again? I always hated changing the DE, since I thought I had to take the thing apart and hose off the individual filter grids each time. Thankfully Pool School taught me that I can get an 80% change just by properly using my multi-port valve

    One final story: I took a water sample into Leslies hoping they could get me CYA and CH numbers. The guy started the chlorine test (using the same DPD chlorine test I have at home) and asks if I've shocked the pool. I said "No, but I've added some chlorine" and he holds up his cruddy-looking test vial and says "look at this, your chlorine is at least 5, probably closer to 8, we can't test your water for you until it's down to 3." Of course, since I've been reading Pool School I actually wanted my FC at 5 or 6 so now I know that Leslies has nothing left to offer me. I said thanks and left the store.

    My pool: 20,000 gallons, in-ground plaster.
    20K gal, inground plaster. Pool was built in 1978 and re-plastered in 2007. 3/4 HP pump. 48 sq. ft. DE filter. Hayward pool cleaner.

  2. Back To Top    #2
    JasonLion's Avatar
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    Re: Need to Shock?

    Chlorine gets consumed by sunlight and in the process of keeping your pool sanitary, so you need to add more every day, or get a SWG or some other kind of automatic chlorine feeder. With CYA around 50, it is normal to lose about 50% of your FC each day. If I am reading correctly, your results are normal, and not organics in the water.

    The filter should be cleaned when the pressure gauge goes up by about 6. You should note down the pressure shortly after adding fresh DE, and then any time the pressure goes up by 6 from there it is time to either backwash the filter or take it apart and do a full cleaning. Even if you did have algae, this same rule applies, algae just makes the pressure go up more quickly.
    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

  3. Back To Top    #3
    Butterfly's Avatar
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    Re: Need to Shock?

    Hi,

    Since your FC dropped to 1, I'd say you left yourself wide open for some problems. That being said, I suggest you do the overnite FC test to see if you have organics eating your chlorine.

    Welcome to the forum
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

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  4. Back To Top    #4

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    Re: Need to Shock?

    Quote Originally Posted by Butterfly
    Hi,

    Since your FC dropped to 1, I'd say you left yourself wide open for some problems. That being said, I suggest you do the overnite FC test to see if you have organics eating your chlorine.

    Welcome to the forum
    Hi Butterfly,

    I brought the FC up to 5 two days ago, it was 3 yesterday, then 1 this morning (after which I brought it back to 5). I have not yet shocked the pool at all this season. Is the "overnight FC test" where you shock the pool until the FC doesn't drop overnight? Also, should I start using tablets (in a floating dispenser) again until my CYA is closer to 70-80?

    Thanks!
    Alec
    20K gal, inground plaster. Pool was built in 1978 and re-plastered in 2007. 3/4 HP pump. 48 sq. ft. DE filter. Hayward pool cleaner.

  5. Back To Top    #5
    MikeInTN's Avatar
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    Re: Need to Shock?

    Alec,

    There may be no need to shock yet. Just bring your FC up to say 5 or 6 at dusk (make sure the sun's off of the pool), and then check it again in the morning before the sun's on the pool. If your FC level drops overnight, then you've still got organics in the pool and will need to shock.

    Unless you've got a saltwater chlorine generator, your CYA is OK at 50, if the strip is reading halfway accurately. So no more pucks.

    hth,
    Mike
    24' x 52" AGP - approx 13,500 gallons
    Pentair Optiflo 1 hp/2sp pump w/ Swimpro Voyager 150 sq ft cartridge filter
    Intex 8110 SWCG
    "Fear the Schnauz!"

  6. Back To Top    #6
    Butterfly's Avatar
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    Re: Need to Shock?

    You do not have to shock your pool to do the overnite test. It's just that most folks that are doing the test are in the process of shocking.

    With your CYA of 50, the range for FC is 4 to 6, never below 4. See the CYA/Chlorine Chart in my sig.

    To accomplish maintaining your FC level, I suggest that each evening after the sun is off your pool, raise your FC to 7 or 8. Each day the FC will drift down, but should not be allowed to drop below 4. Then, the next evening , repeat the process.

    Sometimes folks do not realize that organics & sunshine use up the chlorine and it must be replinished often, usually daily.
    I would say that most of us that use bleach or LC dose our pools each evening.

    Please add your pool/equipment specs in your sig and your location in your profile. This will help members responding to your posts. Info on what we need and how to do this is in Pool School.
    Link in my sig and at the top of each page.

    It would be very helpful if we knew your FC & CC. Do you have another pool store to try - for now?

    Now, the best thing you can do for your pool is get a good test kit. I prefer the TF100 at TFtestkits sold by duraleigh. Link in my sig.

    I know it is a lot to take in at first, but keep reading (Pool School) and asking questions.
    You will be amazed just how easy and trouble free your pool can be. We got a lot of folks around here to help.

    As Mike said, no more pucks!
    TFP Moderator TF100 Test Kit TF100 TestKit YouTube Channel PoolMath
    You're done SLAMing when:
    1)You lose 1ppm or less FC overnight, & 2)You have .5ppm CC's or less, & 3)your water is clear.

    ~ One should not use a sledge hammer to swat a mosquito. ~

    If you found TFP helpful and we saved you money ... Become a TFP Supporter!

  7. Back To Top    #7

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    duraleigh's Avatar
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    Re: Need to Shock?

    I think the problem is probably excess organics still in the pool (although the water looks beautiful) and that I need to shock the pool and keep it shocked until it holds steady.
    The three criteria used to determine if your pool is clear (developed by chemgeek) are:

    1. Your water is crystal clear (sounds like you have that one)
    2. You can hold FC overnite with a .5ppm or less loss. (that's the overnite test)
    3. YOu CC's are .5ppm or less (can you test for CC's?)

    Once you meet those, shocking is not necessary. If you do not meet them, then shock 'til you do.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  8. Back To Top    #8

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    Re: Need to Shock?

    Quote Originally Posted by duraleigh
    1. Your water is crystal clear (sounds like you have that one)
    2. You can hold FC overnite with a .5ppm or less loss. (that's the overnite test)
    3. YOu CC's are .5ppm or less (can you test for CC's?)
    Looks like the pool passes all three. I guess I was just surprised by how much chlorine I need to add every day
    20K gal, inground plaster. Pool was built in 1978 and re-plastered in 2007. 3/4 HP pump. 48 sq. ft. DE filter. Hayward pool cleaner.

  9. Back To Top    #9
    frustratedpoolmom's Avatar
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    Re: Need to Shock?

    Yes, losing 2ppm FC sounds normal to me. Remember to use the chart as your guide, each night or every other night, add enough chlorine to go to the high end of your recommended FC level so that it stays above the minimum FC level for your CYA.
    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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