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Thread: Can't seem to get pH back down

  1. Back To Top    #1

    Join Date
    May 2014
    Location
    Fort Worth, TX
    Posts
    2

    Can't seem to get pH back down

    First, thanks for all the great information y'all provide.

    I just moved into a new house with a 'new to me' pool. I took my water in to be tested about two weeks ago. The numbers the pool store came up with were:

    Temp 85 (sample was close to an hour old by the time we got there)
    FC 8.4
    CC 0.1
    pH 7.3
    TA 84
    Adjusted TA 39
    CH 333
    CYA 151

    My test kit arrived the next day and my numbers pretty much aligned with theirs with exception of the pH:
    Temp 78
    FC 8.2
    CC 0.1
    pH 7.6
    TA 90
    Adjusted TA 31
    CH 330
    CYA 160

    I'd used this pool store for several years, and followed their recommendations and had good success with the pool at my old house. They are half way across town from the new house so I'm trying to do more of this myself instead of finding someone closer that I actually trust. They recommended that I add 31lbs baking soda to get the TA up where it should be and 3 cups muriatic acid. That sounded like an incredible amount to be adding and I was unsure of my volume estimate on the pool so I started with 26lbs and 2.5 cups of acid. I retested 48 hours later and TA had come into range, but the pH had gone too high:

    Temp 76
    FC 7.2
    CC 0
    pH 8.0+ (demand test took 5 drops to get back to 7.6)
    TA 170
    Adjusted TA 115
    CH 330
    CYA 160

    From this point I've been watching the pH daily and adding muriatic acid in small batches (about 3-4 cups at a time) to try to get the pH back in line. After adding nearly a gallon over the last week, this morning's numbers are:

    Temp 76
    FC 4
    CC 0
    pH 7.8
    TA 140
    Adjusted TA 90
    CH 330
    CYA 160

    I know my FC is way low and my CYA is way high. The previous owner used only tabs and I've stopped that. I'd like to do a water replacement, but our water table here in North Texas is very high. I'm hoping to wait until mid summer when we have been very dry so there is less chance of damage during a drain and refill. Now that you've read the book, here are my real questions:
    1. Given my high CYA and what I've read, my target FC should be in the 10-12 range until I can get my CYA down. Is this correct?
    2. Do I just keep adding acid in small batches until I get the pH back in line or should I be doing something different? Just seems like I've added an awful lot in a short time.

    Thanks in advance for any advice y'all have. I've heard you like pictures so:
    photo-small.jpg

  2. Back To Top    #2
    Richard320's Avatar
    Join Date
    Jan 2010
    Location
    San Dimas, CA (LA County)
    Posts
    18,768

    Re: Can't seem to get pH back down

    Welcome!

    That's a beautiful pool; too bad the pool store had to wreck things.

    What test kit did you buy, may I ask? Some of the electronic ones are prone to misreading very quickly.

    You are correct about maintaining the high FC to match the high CYA. Poolmath says 12 is the minimum you should never let FC slip below. The problem with that is, your pH readings will always be suspect; the phenol red drops react with FC over 10 and read falsely high.

    If you plug all your numbers into Poolmath (use Total Alkalinity, not adjusted, whatever that is) and it should tell you how much acid to add to get to a particular pH. If you then scroll down to the bottom, where it says Effects of Adding Chemicals, plug that dose in and it will tell you how much TA will drop with that addition, roughly. You'll see that it will take a while to lower. The high TA - I would have left the first readings alone - combined with your beautiful waterfall will drive pH up really fast, as you've discovered.

    I completely understand not wanting to drain. My first year I was stuck with even higher CYA, and I couldn't drain due to water restrictions. Maintaining a pool with super high CYA can be done, but it's no fun, and I don't recommend it. Anything you can do to lower CYA - use pool water on the lawn, and replace it with the water you would have used on it - will help.
    16K freeform gunite with spa; Pentair 4000 DE filter; Century Whisperflow 1 HP; Pentair Minimax heater.
    Troublefree does not mean Maintenancefree. It's like brushing your teeth: You can spend a couple minutes a day and pennies a week or go to the dentist once a year and spend several thousand dollars.
    A pool is like a pet - you have to feed it every day, even the days you don't want to play with it!

  3. Back To Top    #3
    frustratedpoolmom's Avatar
    Join Date
    May 2007
    Location
    SWSuburban Chicago, IL
    Posts
    11,965

    Re: Can't seem to get pH back down

    Purchase one of the recommended test kits and ditch the pool store's bad advice. Yes, since the pool is clear, you can try and manage with the high CYA as you slowly lower it. Will be tricky, and you need to be able to do your own testing during that time.

    Enjoy your pretty pool!
    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
    http://www.PerfectlyClearPoolService.com

  4. Back To Top    #4

    Join Date
    May 2014
    Location
    Fort Worth, TX
    Posts
    2

    Re: Can't seem to get pH back down

    I got the Taylor K-2006.

    As for the Adjusted Alkalinity. On the last page of the Taylor book there is a table to do TA adjustments based on pH and high CYA. I'm guessing from your comments that I should be targeting TA based on the test reading and not the adjusted value calculated from that table, correct? If that is so, why the table and the formula?

    I'll go with the calculations from PoolMath and see where that takes me.

  5. Back To Top    #5
    JasonLion's Avatar
    Join Date
    May 2007
    Location
    Silver Spring, MD
    Posts
    37,879

    Re: Can't seem to get pH back down

    Adjusted total alkalinity is [u]only[/ul] used for calculating LSI, which we never use. When we talk about TA, we are always referring to the number straight from the test kit.
    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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