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Thread: high clorine demand, low ph

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    high clorine demand, low ph

    Pool had a high demand for chlorine all last summer and some staining issues at the end of the summer before I closed it. When I opened it on April 14th I shocked it with 12lbs. of shock (because of chlorine lock issues last opening) and the next morning only had a free chlorine reading of 3. 12 hrs. later fc was down to 1. I shocked again with 8lbs. 24 hrs. later the numbers look like this. fc 3.4 tc 4.5 ph 6.9 ch 70 alk 100 cya 85. I added 6-8 lbs of ph plus in 24 oz dose but every time the ph hasn't changed.I really think most of my problems might be in the shock and algeacide that I am using. Pool brand shock with 99% Sodium Dicloro-s-Triazinetrione, Pool brand algeacide with dimethyl benzyl ammonium chloride. any help with this would be appreciated. Even if the chemicals I am using are the problem, I have no idea where to start to fix this without draining water.
    24,000 gal. sand filter, IG vinyl liner, 1hp pump unknown flow rate.

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    Re: high clorine demand, low ph

    Please read the Pool School section. You will find darn near every answer to these questions and it will fill in a lot of the holes in your becoming educated about keeping your pool's care in a sanitary state for your family, you, and your guests.

    The use of di-chlor for elevating the FC to shocking levels is generally discouraged. It contains Cyanuric Acid (CYA), aka Stabilizer. Chlorine lock is a myth of sorts. It just means that you have too much CYA to be effective. CYA protects FC from the sun but also can keep it from doing its 2 main functions, killing biologicals and oxidizing organics. You will likely be doing partial drains of your water depending on where you live and how you chlorinate your pool.

    Shocking a pool is a process. You aren't done. Your having used the Di-Chlor just made your shocking all that much more difficult. Switching to Cal-Hypo, chlorinating liquid (typically 10-12%) or 6% bleach, depending on cost, is strongly suggested. You indicated that your CH level was low to begin with or else I would not have added Cal-Hypo as a potential chlorine elevator.

    Algaecides generally only helps prevent algae. Chlorine kills it. Keeping the chlorine up negates it's need in maintaining your water. A good Polyquat-60, if you must, such as in winterizing, is suggested.

    Welcome to TFP by the way. This is one of the best sites I know of on the web for residential pool care. I regularly send my customers here because of this fact. You will not reinvent the where here by following the suggestions given.

    Scott
    Owner of - PoolGuyNJ LLC
    Expert Pool and Spa Repairs, Renovations, and Augmentation. Helping people decide what is the right gear for meeting their needs. Expectations Set, Expectations Met, No Surprises.

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    Re: high clorine demand, low ph

    I can add absolutely nothing to the VERY thorough post poolguynj just made other than to agree completely just for emphasis.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
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    Re: high clorine demand, low ph

    Hi eshill, Welcome to TFP!
    Just as Scott has stated (PoolGuyNJ) follow the instructions in Pool School for proper shocking.
    One of the keys to success is a proper FAS-DPD test kit with CYA testing.
    Read here about info on test kits:
    pool-school/pool_test_kit_comparison

    The most preferred kit for the value is the TF-100.
    If your dealing with a problem pool, it's best to get the XL option for a little extra testing supply's.
    You can order here online.
    http://tftestkits.net/splash-page.html

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    Re: high clorine demand, low ph

    Welome to TFP!

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    Re: high clorine demand, low ph

    Thank you all. I have quit using the shock I was using and shocked the pool with 6% chlorine bleach and it is looking better. I still can't get the ph above 7.0. If anyone knows what the black / brown tar or grease like substance that shows up at the back of my skimmers, at the water line is would be great. It doesn't seem to be showing up as quickly now as it was a day or two ago. When I clean it off it would show up an hour later.
    I also ordered a tf-100 test kit, thanks so far for the good advice.
    24,000 gal. sand filter, IG vinyl liner, 1hp pump unknown flow rate.

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    linen's Avatar
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    Re: high clorine demand, low ph

    Welcome to tfp, eshill

    I am not sure you are shocking per the procedure on this forum. Review the procedure, you are not done until you pass all three criteria mentioned. http://www.troublefreepool.com/pool-...king_your_pool It is a process and not a one time application of chlorine. It is possible that doing this process could eliminate the "grease" you are referring too.

    You can deal with the ph when your are done with the shocking process.
    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: high clorine demand, low ph

    The dichlor you were adding was constantly lowering the PH. Now that you have switched to bleach it should be possible to get the PH to come up.

    Also, how recent is your CYA test result? Using dichlor tends to raise the CYA level fairly quickly. Higher CYA levels mean you need to use more chlorine to get the same effect.
    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: high clorine demand, low ph

    "If anyone knows what the black / brown tar or grease like substance that shows up at the back of my skimmers, at the water line is would be great. "

    I really cannot say, with certainty, but I get a greasy black "bath tub ring" when someone is burning something. Most likely trash. The smoke rolls in and I get a ring on the tile and in the skimmers. I have also suspected carbon black from the tires and maybe some sort of exhaust as there is a good bit of traffic around here. Whatever it is, a Mr Clean eraser thing takes it off.
    My cement pond is a 36K gunite 20X40 built in mid 1960s, Hayward S244S filter, Aquarite SWCG, Jandy 1.5HP 2sp, TF-Test kit and Nitro Wall Climber

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    Re: high chlorine demand, low ph

    Reading on hear was why I switch to bleach (thank-you) but do you think I will have to drain a lot of water for the cya to go down? The test result is fairly recent, 3-4 days ago. The black stuff in the skimmer I agree will burn off with proper shocking but I just wanted to know what it was. It is not around my pool only in the skimmer and you can see it form from what looks like drops of oil that form bubbles.I think it is coming from the algeacide I was using.
    24,000 gal. sand filter, IG vinyl liner, 1hp pump unknown flow rate.

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    Re: high clorine demand, low ph

    The chlorine will get rid of that black stuff. Who knows the source but, as you continue to read, you will find that using only chlorine (bleach) in your pool is gonna' get you in good shape.

    If your cYA of 85 turn out to be accurate, (wait on your kit) then, yes, we would like to see you get it down to about 50 to really make your pool manageable, but that will only be like somewhere around a 30% drain.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: high clorine demand, low ph

    I guess I should go ahead and do a partial drain now that way when my tf-100 kit comes I can check all levels and proceed shocking from there. Then balance after a chlorine loss test.
    24,000 gal. sand filter, IG vinyl liner, 1hp pump unknown flow rate.

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    Re: high clorine demand, low ph

    I guess I should go ahead and do a partial drain
    Probably. BUT, if those test results are from a pool store, I think I would wait until you get the kit (PM me your name and I'll tell you when it will get to you) and test it yourself.

    There is a chance the CYA is lower than that test and you may not have to drain. That said, if you want to get a jump on it, it is quite easy to add more CYA....it's reducing it that is such a hassle.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: high clorine demand, low ph

    CYA was 90 so I did about a 45% drain and left 10 inches in the shallow end, just finished filling about 5 hrs ago. Early CYA test is 50, will test tomorrow since pump was only running for 5 hrs. I did run robotic cleaner to help mix water.
    CYA-50
    FC-1
    CC-1
    TC-2
    PH-7.0
    TA-70
    CH-90
    24,000 gal. sand filter, IG vinyl liner, 1hp pump unknown flow rate.

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    Re: high clorine demand, low ph

    VERY nice work Bring your FC up to about 3-4ppm. How does your water look?
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: high clorine demand, low ph

    Water looks very clear. Will 18 hrs be enough circulation time to get accurate test results so I can balance? Thanks for all the help and I already see the value of a good test kit.
    24,000 gal. sand filter, IG vinyl liner, 1hp pump unknown flow rate.

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    Re: high clorine demand, low ph

    An hour of run time is all you need.
    Dave S.
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    Re: high clorine demand, low ph

    Definitely get some more FC in there tonight ... up to the 4-6ppm range. I'd say 2 gallons of 6% bleach should get you close to 6ppm. (have you played with the poolcalculator.com yet?)
    With a CYA of 50ppm, you never want to let it drop below 4ppm.

    In fact, it would not hurt to do the overnight chlorine loss test to confirm there is nothing living in your pool.
    Jason, TFP Moderator
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