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Thread: Should minimum FC level be maintained while shocking?

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    Should minimum FC level be maintained while shocking?

    I have about 35 CYA so my shock level is 14. I started shocking yesterday and it dropped 2 overnight and during the day I loose anywhere from 2 to about 4 per hour (its a hot sunny day here in east tenn).

    I read when shocking that we should check the FC every hour or so and bring it up to the recommended level. I've been watching the use rate and am adding bleach to the extent that after an hour or so the FC has been used up and is around the min level. Then I add enough bleach to bring it up so that it should be around the min level after another period of time.

    [1] Is this method good, bad, or doesn't matter?
    [2] Are my FC loses as expected?
    [3] Any other suggestions?
    18X36 IG vinyl 22100 gal. 1.0 HP Hayward Pump w/300# Hayward sand filter.

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    Re: Should minimum FC level be maintained while shocking?

    How often to check depends on how fast it's dropping, but waiting until it gets all the way down to the minimum is too long. Every 2-3 hours is probably about right. The better you are at keeping the FC up, the quicker the process will go.
    --paulr
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    Re: Should minimum FC level be maintained while shocking?

    I read when shocking that we should check the FC every hour or so and bring it up to the recommended level.
    I want to make sure we're on the same page terminology-wise...


    If your suggested shock level is 14ppm, you should make every effort to keep the FC at 14 constantly until the pool is clear.

    In the initial stages of the shock process, I suggest it's a good idea to exceed the suggested level by say maybe 15%. That means you would bring FC up to around 16 or so because it will be passing back down thru 14 very quickly.....it gives you a little longer to test in between doses.

    However, you decide to test and dose, remember that it is important to hold your FC up around shock level as often as you can. Thats what will make your pool clear up quickly.
    Dave S. - Forum owner
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    Re: Should minimum FC level be maintained while shocking?

    I've been shooting for about 16-18 knowing that based on my burn-up rate it will most likely be around 14 the next time I test. Based on that number I've been adding bleach to keep my FC at a level that should still be 14 by the next test interval. I went to about 20 yesterday because I had to leave for a few hours and didn't want it to decay below 14 while I was gone. By the way, CC is maintaining 0 during all this.

    Does that sound right? Also, the other part of my question is if my usage rate looks about right or do I have something else going on.

    That reminds me with all this testing I need to order more chlorine test agents.
    Thanks
    18X36 IG vinyl 22100 gal. 1.0 HP Hayward Pump w/300# Hayward sand filter.

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    Re: Should minimum FC level be maintained while shocking?

    You seem on the right track but don't tell us why you are shocking. I assume you are having some water quality issues?

    So, you keep the FC up at shock value and will have completed the process when.......

    1. Your pool water is sparkling
    2. Your CC's are .5ppm or less
    3. You can hold your FC overnight without losing more than 1ppm.

    How does your water look?
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: Should minimum FC level be maintained while shocking?

    Are you testing AFTER adding the bleach to see if you have reached your target?
    What brand of bleach are you using?
    Helpful links: Pool School; CYA/Chlorine Chart
    24' round AG pool, 52" high, Raypak heater; Waterway 2 spd Pump;
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    Re: Should minimum FC level be maintained while shocking?

    First, thanks for the help...

    I'm shocking because [1] I was loosing all my FC from evening to evening. The CCs remained at 0. [2] I had small amounts of green algea appearing around the returns, the skimmer basket opening, and on the liner seams. Latest information is...As of last night FC was 16, CC was 0 about 1.5 hrs before sunset. At 07:40 this morning before the sun hit it the FC was still 16 with CC of 0. Yea!

    I don't test right after adding because I wasn't sure the water/bleach had adequately mixed. I'm using the 182 oz Dollar General Value Regular Bleach which the label list as 6% sodium hypochlorite. $2.50 a jug. I performed a FC/CC test at the end of a particular interval, 1-2 hours after adding bleach. I then add the amount of bleach based on the Pool Calculator figuring a jug this size for my pool with CYA of 35 jug would increase 4 ppm. I use an amount to account for my expected decay/use rate from that interval till my next prescribed test time. Now I'm running low on test agents with more on order. Based on previous experience with TF Test Kits they'll ship tomorrow. Is there a way to adjust the water sample to 5ml and that way only use 1/2 the agent until I get my replacement? But that probably throws off the .5 multiplier. Any suggestion for that?
    18X36 IG vinyl 22100 gal. 1.0 HP Hayward Pump w/300# Hayward sand filter.

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    Re: Should minimum FC level be maintained while shocking?

    [2] I had small amounts of green algea appearing around the returns, the skimmer basket opening, and on the liner seams.
    Interesting, that's the first place it shows up in my pool, as well. It points out how much algae loves little nooks and crannies.

    Your refills will ship tomorrow.

    CYA of 35 is perhaps a tad low. If you experience FC loss of noticeably greater than 2ppm daily (after you shock) then you might consider bumping it up some.

    I run my pool around 50ppm and it has made a very big difference from last year when I tried 30ppm.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: Should minimum FC level be maintained while shocking?

    I was seriously considering increasing my CYA. I opened a subject the other day Re:"Using Trichlor pucks to increase CYA" since I have 6 or so pucks left. Once I get through shocking, which I may be since my FC stayed constant overnight and I have 0 CCs, I may load the pucks in the chlorinator and let 'em go. Then I'll see where that puts me for CYA and go from there. Last year I had a CYA of around 60-70 and loss about 1-2 ppm a day. Also last year I asked re: "CYA levels for sunny pools" where a reply was that I could go 60-80 for an all day sunny pool.

    Thanks again
    18X36 IG vinyl 22100 gal. 1.0 HP Hayward Pump w/300# Hayward sand filter.

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    Re: Should minimum FC level be maintained while shocking?

    There are advantages and disadvantages to using higher CYA levels. You will use less chlorine day to day at higher CYA levels, but shocking the pool can require dramatic amounts of chlorine.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Should minimum FC level be maintained while shocking?

    Okay, when shocking to defeat algae, it's always good to follow up about 30 minutes after adding bleach to see if you reached your shock target.

    Also we generally don't recommend dollar store bleach or Big Lot's bleach because we have reports of bleach that is old or has lost it's strength, or is not 6%.

    There are several threads where a person is trying to shock and not making progress, and we were able to narrow it down to a lower % bleach (like 3%) or old bleach that has been sitting around since last year. In general, I'd recommend avoiding that supply and getting your bleach from Wal-mart, Target, generic store brands they carry, or similar locations. Aldi bleach is good too.

    Just an FYI.
    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
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