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Thread: SLAM and pH strangeness

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    Join Date
    Oct 2013
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    Austin, TX
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    SLAM and pH strangeness

    Hi all, this is our first summer with our new pool (built in October); it is hot and very humid here in TX. I have been a diligent follower of the methods here since we built the pool.

    Last week, we came back from a five-day trip and had some heavy cloudiness in the pool; brushing revealed some green-ish/yellow-ish bubbles on the surface, so I SLAMed. During the SLAM, I brushed and backwashed. Everything cleared up in two days and I passed the tests. Current numbers are (via TF100):

    FC (FAS-DPD): 3
    CC: (FAS-DPD): 0.5 or less (just very barely turns pink when starting the CC test)
    pH: 6.8
    CYA: 55
    TA: 80

    Two things struck me as odd after the SLAM:

    1. The pH has dropped precipitously, and seems to want to stay there. Previously, I would add about half a jug (the pH in our pool falls constantly, which I understand is common with salt pools) to get from low pH (7.2-ish) up to 7.6-7.8 range. Now, half a jug does almost nothing. I've added half a jug the last two days, and seen no movement up from 6.8. I am getting ready to add quite a bit today, but is this normal to see the pH suddenly become very stubborn after a SLAM?

    2. My TA has dropped a lot. For the entire 10 or so months that the pool has been in operation, it's been stuck in the 110-120 range (last few readings have been 110). I did some aeration about a month ago after reading here (somewhere) that SWGs were more efficient at a lower TA, but it never went below 110. Now it's dropped a lot, and I'm wondering if it's connected to the sudden stubbornness of the pH.

    Finally, I'm wondering if anyone has much experience with SWG percentage/pump runtimes in hot climates. Pool is in full sun and is now pretty warm (~87 degrees). It seems like a have to run the SWG at 60-70% to keep up. Pump is running 9 hrs per day at 1500 rpm. Any suggestions on runtime or best practices would be greatly appreciated. Thanks!
    17K Gallon Gunite Pool, 3M Quartz finish, Jandy VS Pump, Jandy 30" Sand/Glass Filter, AquaPure SWG, Trident UV Sanitizer, Polaris 280, iAquaLink.

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    Isaac-1's Avatar
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    Re: SLAM and pH strangeness

    Just a couple of things, first you really need to get the pH right away. Second you should be aware that the pH test results are not valid during a SLAM with FC levels over about 10 ppm
    Indoor 20x40 35,000 gallon vinyl pool with 1.5 HP 2 speed Jandy FloPro pump, Hayward EC75 Perflex DE filter, 11 4x12 Techno-Solis solar panels w/ Aquasolar controller, Aquabot Turbo T Robot Cleaner. Also LMI metering chlorine dispenser pump and HotSpring Jetsetter
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    JasonLion's Avatar
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    Re: SLAM and pH strangeness

    Typically with a SWG an TA around 100 you will be constantly adding acid because the PH is too HIGH. Your PH is too LOW. It seems like you might be mixing up low and high?

    The common chemicals for raising PH are all powders (soda ash, borax). So I wonder why you are mentioning using a jug? Perhaps you are mistakenly adding acid (often a liquid) and lowering the PH even further?

    SWG percentage settings vary dramatically from pool to pool. You have to find the setting that works for your situation.
    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: SLAM and pH strangeness

    Sorry, I think I got it backwards. My mistake. I guess I really screwed up now because I added more acid today. I have it all backwards! I'm so used to adding acid that I thought it would fix the low number, not realizing I'm already too low. So, now it's probably so low that we can't swim in it for a while. Ugh.

    Thanks for clearing that up.
    17K Gallon Gunite Pool, 3M Quartz finish, Jandy VS Pump, Jandy 30" Sand/Glass Filter, AquaPure SWG, Trident UV Sanitizer, Polaris 280, iAquaLink.

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    Richard320's Avatar
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    Re: SLAM and pH strangeness

    Quote Originally Posted by brentb View Post
    Sorry, I think I got it backwards. My mistake. I guess I really screwed up now because I added more acid today. I have it all backwards! I'm so used to adding acid that I thought it would fix the low number, not realizing I'm already too low. So, now it's probably so low that we can't swim in it for a while. Ugh.

    Thanks for clearing that up.
    You can fix things up quick with some baking soda and borax. Within a couple hours, easily. Just allow things to mix well before retesting and re-dosing. Remember to take half-steps, since poolmath isn't accurate for huge changes.
    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.
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    elwood58's Avatar
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    Re: SLAM and pH strangeness

    You will also find that if you get your CYA up a little, to at least 70, you should be able to back off the percentage on the SWG. That is also dependent on what size cell you are running, relative to the size of your pool. cell should be rated at least double your pool volume.
    19204 Gallon L Shape with a 10X10 2nd Step Baja Ledge. Intellichlor IC-40, IntellipH, Cartridge Filter, Pentair Heater/Chiller (Heat Pump). Tons of Deck with Deck Jets. Construction Complete 6/5/17.

    "If you don't measure it, you can't manage it!"

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    Re: SLAM and pH strangeness

    Thanks for all your help. We have a separate (bromine-sanitized) Bullfrog spa and I am always having to raise the pH on that, so that's probably where I got confused. Too much chemistry for an old man!

    I will increase the CYA over the next week. Is there any reason to mess around with the TA at this point?
    17K Gallon Gunite Pool, 3M Quartz finish, Jandy VS Pump, Jandy 30" Sand/Glass Filter, AquaPure SWG, Trident UV Sanitizer, Polaris 280, iAquaLink.

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    elwood58's Avatar
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    Re: SLAM and pH strangeness

    TA is within the recommended range of 60-80. Once you get things stable you can drop pH to 7.2 and aerate it back up to 7.6. This will drop your TA.
    19204 Gallon L Shape with a 10X10 2nd Step Baja Ledge. Intellichlor IC-40, IntellipH, Cartridge Filter, Pentair Heater/Chiller (Heat Pump). Tons of Deck with Deck Jets. Construction Complete 6/5/17.

    "If you don't measure it, you can't manage it!"

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