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Thread: Why Does the pH of My Pool Constantly Drop?

  1. Back To Top    #1

    Join Date
    Oct 2007
    Location
    Philadelphia, PA
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    Why Does the pH of My Pool Constantly Drop?

    I hear most people need to constantly add acid to their pools as the pH rises. The pH of my pool always goes down. I have never added acid and am constantly adding washing soda. Typical test results:
    FC: 3 to 6 ppm depending on the time of day
    CC: 0 ppm
    TA: 80 ppm
    CYA: 40 ppm
    pH: 7.4

    I'll bring the pH up to 7.6 with washing soda and over about 10 days it drops again to 7.2. Repeat every 10 days. Pool is kept covered when it's cool out and uncovered when it's warm. I notice no difference in the rate of pH change with the cover on or off.

    Any ideas?
    11x27 in ground, vinyl pool
    ~12,500 gal
    PAC FAB (Pentair) Pinnacle 3/4 hp pump
    Pentair 24 sq ft DE filter
    One skimmer, one return (no main drain)

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    Jul 2011
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    St. Paul, MN
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    Re: Why Does the pH of My Pool Constantly Drop?

    What type of chlorine do you use in your pool? If you use trichlor, that will lower your pH.
    20'x40' Oval 27,000 gallon Vinyl IG, Coverstar Auto Cover
    Hayward MaxFlo SP2303VSP, Sta-Rite PLD50 30 sq. ft. DE filter
    Rheem 266,000 btu natural gas heater
    Dolphin Nautilus Plus with Clever Clean
    TF-100 testkit w/ Speed Stir

  3. Back To Top    #3

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    Oct 2007
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    Re: Why Does the pH of My Pool Constantly Drop?

    I use liquid chlorine -- the 182 oz bottles of Chlorox from Costco. I need to add between 1/3 and 1/5 bottle each day.
    11x27 in ground, vinyl pool
    ~12,500 gal
    PAC FAB (Pentair) Pinnacle 3/4 hp pump
    Pentair 24 sq ft DE filter
    One skimmer, one return (no main drain)

  4. Back To Top    #4

    Join Date
    Jul 2011
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    St. Paul, MN
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    Re: Why Does the pH of My Pool Constantly Drop?

    Besides bleach and washing soda, is there anything else that you add to your pool on a regular basis?

    With your TA at 80, it seems to me that your pH should be fairly stable.
    20'x40' Oval 27,000 gallon Vinyl IG, Coverstar Auto Cover
    Hayward MaxFlo SP2303VSP, Sta-Rite PLD50 30 sq. ft. DE filter
    Rheem 266,000 btu natural gas heater
    Dolphin Nautilus Plus with Clever Clean
    TF-100 testkit w/ Speed Stir

  5. Back To Top    #5
    linen's Avatar
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    Jul 2010
    Location
    Twin Cities, MN
    Posts
    8,649

    Re: Why Does the pH of My Pool Constantly Drop?

    What is the history on your TA? If you are regularly adding washing soda and your not adding chemicals that are acid sources (MA, ph down, trichlor, dichlor, etc.), then your TA should also be going up.

    How much make up water are you putting in to the pool (do you have an autofill)? This would be unusual, but if the makeup water is lower in TA and higher in ph, and you are using quite a lot of it, that could cause what you are seeing.
    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.

  6. Back To Top    #6

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    Philadelphia, PA
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    Re: Why Does the pH of My Pool Constantly Drop?

    I haven't added anything other than bleach and washing soda since opening several weeks ago. TA does creep up over the season and typically is a bit over 100 by the time I close in the fall.

    There is no autofill. The makeup water is mostly rain -- it's been raining regularly here. I can't believe the pH of a 1/2" of rain water would change the pool pH measurably. I did need to add a bit of tap water right after opening, but was also around 1/2".
    11x27 in ground, vinyl pool
    ~12,500 gal
    PAC FAB (Pentair) Pinnacle 3/4 hp pump
    Pentair 24 sq ft DE filter
    One skimmer, one return (no main drain)

  7. Back To Top    #7
    frogabog's Avatar
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    Jul 2010
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    Portland, Oregon
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    Re: Why Does the pH of My Pool Constantly Drop?

    Rain lowers my pH too. Doesn't seem like it would, but sure seems to. Have you tested the pH of your rain? However, does this occur when there's no rain? Is there perhaps a left over trichlor puck in a feeder or is some well meaning person adding trichlor that you don't know about? (seriously, I know it sounds silly to ask but last year a forum member actually had this happen, a kid was trying to "help")
    Where kids swim in 54 degree water, turn blue, and giggle happily cuz they got a POOL!
    Year 3 BBB -15' x 48" Intex Metal Frame - Was using (2) 1000gph Intex cartridge filters (see Full time pumping Intex). 2012, converted to 1600gph and sand filter+SWG = Sand filter love affair!
    Don't waste time and energy looking for a better value on test kits, the TF100 is the best deal around. I did the looking and spent the extra money, but you don't have to make the same mistake. Just go here: TFTestkits. I use Pool Calculator for min/max, and shocking chlorine levels.

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    JasonLion's Avatar
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    Re: Why Does the pH of My Pool Constantly Drop?

    That doesn't make much sense. Still, raising the TA should take care of it (as long as you raise TA enough).
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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