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Thread: Strange Chlorine loss

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    Strange Chlorine loss

    I have been getting some very strange chlorine readings in my pool, and I have run out of ideas. So I'm turning it over to the sound advice of you all here. I will try to make a long story as short as possible.

    I use a Taylor Test Kit.
    MY FC I normally keep about 6, based on my CYA of 43.

    I normally check my FC and PH about every other day, just because I know my pools habits. I usually add about a third of a gallon of bleach per day which replaces a consistent 3ppm FC loss due to sunlight.

    So about three weeks ago I took the cover off for the first time this season. There was quite a bit of gunk in the water, but I ran the vaccume for a few hours, and everything looked great. All numbers were great. I put the cover back on, and left it on.

    This Wednesday, I went to do my normal chlorine check and it was 0. Uh oh, something is eating it, so I began the shock process, bringing FC up to 18. Overnight, I had a 6 point loss! Bad! So, I took off the cover to see if something weird was under there, and sure enough, a big dead bloated gopher! I got him out. The water looked off. Not horrible, but a bit murky and not sparkly like it should. CC was 0.

    I continued to shock, assuming the dead gopher was causing all this. That night, another 6 point loss, but the next day the water looked great. Sparkly, beautiful.

    Here is where it gets weird: I figured the worst was over and things would stabilize. The weekend rolled around and I was able to test more frequently. Wanting to keep things at shock level, I did a test mid-day, and I was shocked to find a 6 point drop in only three hours! Then I noticed how much bleach I was going through; way more than I did last time I shocked. I had used 10 gallons in three days! So I test FC; it had again dropped from 18-13 in just a few hours. I poured in a whole gallon of bleach to really bump it up high. An hour later, I had only moved from 13-15 with a gallon of bleach! This strange massive chlorine loss/inability to raise it continued all weekend. Now I've been shocking for four days; and I've run out of titrating reagent, so everything might have been for nothing. I don't know if the pool held last night or not because I ran out of agent right in the middle of my morning test.

    Then this morning I noticed a small leak on under the pool heater. I remembered that I thought we had been losing water much more rapidly than normal in the pool. The leak looks like it has been there for a few days at least.

    I'm very stumped with this. The water looks fantastic, but this massive chlorine loss and inability to raise it is very strange. I thought after four days of shocking with the water looking this good, things would stabilize.

    Could the leak have something to do with this weirdness?

    Sorry for such a long post, but I wanted everyone to have as much info as possible.
    Test Kit: Taylor K-2006
    Pool:In ground/Pebble/16,000 gal/Cartridge Filter/Pool Built appr. 1995-2000

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    JasonLion's Avatar
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    Re: Strange Chlorine loss

    The leak might have something to do with it, but that is unlikely.

    {{{Ignore the rest of what I said before.}}}
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Strange Chlorine loss

    Yes, 43 was an a slight rounding up from 40. I was getting "around 40", but to my eye it seemed "on the high end of 40", so I tried to round it up just a bit to be on the conservative side (I run my FC on the high end of recommendations and of any estimation). Very hard to be precise with this test.

    Still, the 6 point loss overnight with crystal clear water; is that heard of?
    Test Kit: Taylor K-2006
    Pool:In ground/Pebble/16,000 gal/Cartridge Filter/Pool Built appr. 1995-2000

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    Re: Strange Chlorine loss

    When I first found this site I was having the same type of problem as you have. It took me a little over a week to complete the OCLT. My water never was cloudy, the CC never measured more than .5, but the pool would not hold chlorine for very long.

    I would say something was growing in the pool as a 3 ppm loss a day with a cover seems a little high. Then the gopher ordeal lead to conditions to take off from there. Order some more reagent and try to keep up with the bleach the best you can.
    16k gal plaster with raised spa, Jandy DEV60 filter, 2 HP 2-speed SHPF Jandy Stealth pump
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    Test Kits . Pool Math . Chlorine/CYA Chart . The SLAM Process

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    Re: Strange Chlorine loss

    Ping: That is very helpful. Good to know that this has happened to someone else, and you have a time-reference for how long it took to fix. Thanks!

    Oh, and I need to clarify: the 3ppm loss was when the cover was not on. When the cover was on, it was less than half that, and only during the day did I lose; that was before all this weirdness when everything was 'normal'.
    Test Kit: Taylor K-2006
    Pool:In ground/Pebble/16,000 gal/Cartridge Filter/Pool Built appr. 1995-2000

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    JasonLion's Avatar
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    Re: Strange Chlorine loss

    Did you just open for the season?
    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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    Re: Strange Chlorine loss

    About three weeks ago I opened.
    Test Kit: Taylor K-2006
    Pool:In ground/Pebble/16,000 gal/Cartridge Filter/Pool Built appr. 1995-2000

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    JasonLion's Avatar
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    Re: Strange Chlorine loss

    Yes, this is sounding stranger and stranger. You would need a really massive leak to account for that much chlorine loss, and you would certainly notice that significant a leak. Rapid chlorine loss sometimes occurs when you first open, but when that happens you can't measure any FC level at any point.

    Have you been brushing the pool during this period? A biofilm on the walls/floor could cause some chlorine loss. Brushing will disrupt any bio-film that might be present.
    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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    Butterfly's Avatar
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    Re: Strange Chlorine loss

    Can you post a full set of test results? Esp interested in FC and CC.


    Having crystal clear water and failing the OCLT is quite common.
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    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.

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    Re: Strange Chlorine loss

    Sorry: I should have posted standard test results at the beginning:

    Yes, I have been brushing, even though there is nothing to brush.

    The test results: Not sure what to post because this has been over a long period of time.

    The results before all this happened and everything was "normal" were:

    CYA: between 40-45. I rounded to 43
    FC: 6
    CC:0
    Ph: 7.7
    CH: 300
    TA 90

    Since I've started shocking, I've been trying to keep it between 16-18, but as I mentioned, I have been having trouble doing that because it is dropping so darned fast. I'm sure I've dropped down to about 13 a couple of times just because I wasn't there watching it all day. I raised the FC up to about 20-21 before I go to bed, just so it doesn't drop below shock, and by morning it is at 15-16. I'm having to add over a gallon of bleach (sometimes 2) every time I want to get it to go up just by about 4 points, for example, when I bump it up from 16 to 20 at night before I go to bed.
    Test Kit: Taylor K-2006
    Pool:In ground/Pebble/16,000 gal/Cartridge Filter/Pool Built appr. 1995-2000

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    Butterfly's Avatar
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    Re: Strange Chlorine loss

    Did you record CC with the FC on your earlier tests?
    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!

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    Re: Strange Chlorine loss

    Yes, CC has always been 0. Never changed.
    Test Kit: Taylor K-2006
    Pool:In ground/Pebble/16,000 gal/Cartridge Filter/Pool Built appr. 1995-2000

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    JasonLion's Avatar
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    Re: Strange Chlorine loss

    The CYA test should be read to the closest mark on the tube, without any attempt to estimate positions between marks. The CYA test simply isn't precise enough to get any more information than that out of the result.
    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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    Re: Strange Chlorine loss

    Okay, if I shouldn't round, then I will say the CYA was 40. It came out closer to 40 than to 45 every time I read it.

    I do appreciate all the help. Even just hearing that OCL with clear water is not uncommon at least lets me know that I'm not going crazy.
    Test Kit: Taylor K-2006
    Pool:In ground/Pebble/16,000 gal/Cartridge Filter/Pool Built appr. 1995-2000

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