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Thread: Where is my chlorine going?

  1. Back To Top    #1

    Join Date
    Sep 2014
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    Chelmsford, MA
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    Where is my chlorine going?

    We opened our pool a few weeks ago here in Massachusetts. Since we closed late and opened early we only had some silt/leaves/dirt to pull out and the water got to clear in a few days.

    Salt was low (needed 90lbs), TA was high (120), CYA was low (40), and PH was a little high (7.8) CH I don't pay much attention to as I have a vinyl pool, my next round of testing I'll test CH.

    We had a pool party last Saturday, the day of the water was crystal clear, the filter was running fine and everything was great. A few kids had some itchyness in the covered area, but they spent the day wet from 2pm to 10/11pm so that wasn't so surprising to me.

    The night before the party I did a "boost" on the salt cell and let it run 24 hours.

    The next day I put in 2 gallons of 8.25 bleach to counteract the load and went to bed with the filter running.

    The next day the Chlorine levels on the simple test read around the 10 mark. I stopped boosting, let it go back to it's normal routine, oops overshot, no one went swimming because it rained anyway.

    A day later the Chlorine levels were in the .5/.5 ranges, water is crystal clear (has not changed from that) Sides are not slimy. Water temp is up around 80 currently (during the party it got to 88 degrees)

    The last few days I have been unable to get the Chlorine levels up. Monday I put 2 more gallons of bleach in to try to give it a boost, tested the next day and was at nearly 0 again.

    Last night I put in 6 gallons of bleach (8 gallons or so should bring me to 20 FC, the suggested number for a SLAM).

    This morning it read as 1 or so. This afternoon we are at 0.

    I took my water on Monday to the local pool store to double check my test kit, and their numbers matched mine. I added 40lbs of salt last night to get up to the 3k target. (needed 20-25, overshot by a little)

    I'm concerned the salt cell needs attention, but have never done anything to it (only our 2nd full year starting now).

    Thoughts? Where is this chlorine going?


    My wife is insisting to take the water to another pool store and thinking about taking whatever advice they have for us. I need to do a full suite of tests again tonight to see where we stand. I was going to add more bleach tonight but as it all just went away overnight I don't want to keep tossing money away.

    The solar cover is not on the pool yet.
    21,600 Gallon IG vinyl L shaped Pool
    Hayward DE3620 Pro-Grid DE Filter, Hayward 1HP super pump, AutoPilot SWG, 350,000BTU Hayward Heater
    TF-100 Test kit with options (salt strips, Borates, mixer)
    9/30/14 Dig Began....

  2. Back To Top    #2

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    Re: Where is my chlorine going?

    You need to shut off the salt cell tonight. You'll be adding bleach, so be prepared... Then, perform the OCLT.

    Pool School - Perform the Overnight FC Loss Test (OCLT)
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
    If TFP has helped you, please click to SUPPORT TFP!

  3. Back To Top    #3

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    May 2016
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    Cincinnati, OH
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    Re: Where is my chlorine going?

    Quote Originally Posted by rks1789 View Post
    .. CH I don't pay much attention to as I have a vinyl pool, my next round of testing I'll test CH.....
    I did notice in your signature that you have a gas heater, so might want to pay attention to CH. just saying.
    30000 gal inground vinyl liner;sand filter w/glass media, nuvo uv, TF-100 test kit; 25 years on Baquacil, converted to TFP chlorine in 2016

  4. Back To Top    #4

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    Re: Where is my chlorine going?

    Quote Originally Posted by pookiesunshine View Post
    I did notice in your signature that you have a gas heater, so might want to pay attention to CH. just saying.
    Only if warranty says you have to, and even then how would they know?
    Built in 1957 44,000 gallon in-ground, Wet Edge Primera Stone in Sky Blue, Intelliflo VF Pump, 600 lb. Pentair Triton II TR-100 Sand Filter, CircuPool RG 60 Plus SWG, TF-100 test kit
    If TFP has helped you, please click to SUPPORT TFP!

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    May 2016
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    Cincinnati, OH
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    Re: Where is my chlorine going?

    i was thinking about scaling in the heater plumbing that would reduce heat transfer efficiency, not concerned about warranty.
    30000 gal inground vinyl liner;sand filter w/glass media, nuvo uv, TF-100 test kit; 25 years on Baquacil, converted to TFP chlorine in 2016

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    Join Date
    Sep 2014
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    Chelmsford, MA
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    Re: Where is my chlorine going?

    So my salt strips are out of date and I don't trust them.
    Pool store test showed the rain we got the other day had a major impact on salt levels, or the test I did and a different pool store did were off.

    So we added another 120lbs of salt Wednesday and let it run in "boost" overnight, Thursday night's numbers:
    FC .5
    CC .5
    TA 100
    CH: went to test my blue bottle is clogged somehow
    CYA: 50 (need to boost this up a bit)
    PH 7.4 (a hair lighter than the 7.5 mark)

    I plan on backwashing, but the pressure guage is showing clean filter operation, but I need more DE before I can do that.
    Water is still crystal clear, but I'm paranoid that I can't get that FC number up.

    If adding 6 gallons of bleach didn't get the FC up any overnight I don't know how to SLAM... or I have an issue somewhere else.
    21,600 Gallon IG vinyl L shaped Pool
    Hayward DE3620 Pro-Grid DE Filter, Hayward 1HP super pump, AutoPilot SWG, 350,000BTU Hayward Heater
    TF-100 Test kit with options (salt strips, Borates, mixer)
    9/30/14 Dig Began....

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    Re: Where is my chlorine going?

    Where is this chlorine going?
    Chlorine is a consumable item. It is consumed by organics (usually algae) in your pool or from UV rays from the sun. That's where your FC is going. You must adopt that consumption idea and then you can begin to control the FC in your pool.

    If your wife takes the pool store route, you will take a big setback....both in the knowledge you can learn here and especially in your pocketbook. Don't try to mix the advice......they don't work well and you end up in the muddled middle.

    The boost feature on your SWG is a poor way to SLAM. I suggest you shut it off.

    Can you post a full set of test results (including CYA)?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

  8. Back To Top    #8

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    Re: Where is my chlorine going?

    Quote Originally Posted by duraleigh View Post
    Chlorine is a consumable item. It is consumed by organics (usually algae) in your pool or from UV rays from the sun. That's where your FC is going. You must adopt that consumption idea and then you can begin to control the FC in your pool.

    If your wife takes the pool store route, you will take a big setback....both in the knowledge you can learn here and especially in your pocketbook. Don't try to mix the advice......they don't work well and you end up in the muddled middle.

    The boost feature on your SWG is a poor way to SLAM. I suggest you shut it off.

    Can you post a full set of test results (including CYA)?

    We went to the pool store to have the water checked, I know better than to use that stuff, I only get DE and sometimes CYA from there.

    I also understand that Chlorine is a consumable and what are typical (sun/growth) consumers. What I can't figure out is what is consuming it.

    I was not using the boost to SLAM, just to recover from high bather load, which is what I have used it for in the past. When that failed I tried 8.25 bleach and still can not get the numbers up.

    We went last night and got the water tested again to make sure my test results are accurate, and we were within a small margin on all tests:

    FC .16
    TC .16
    CC 0
    PH 7.3
    TA 125
    CH 136
    CYA 36
    Total dissolved solids 1000
    Salt 4200
    Saturation index -0.3
    copper 0

    I know that the salt is now high, and so is the TA. We are going to get driving rain tomorrow so I'm waiting for that to take care of that for me.

    I backwashed and replaced the DE yesterday, and shifted the SWG output to 75% and ran it "normal" overnight, I just tested the water with the quick test (sports to get to...) and it was still in the less than 1 (but not 0) range this morning.

    The water is as clear as I have ever seen it, and the sides of the pool are not slimy at all.
    21,600 Gallon IG vinyl L shaped Pool
    Hayward DE3620 Pro-Grid DE Filter, Hayward 1HP super pump, AutoPilot SWG, 350,000BTU Hayward Heater
    TF-100 Test kit with options (salt strips, Borates, mixer)
    9/30/14 Dig Began....

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