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Thread: Why the need for acid?

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    Isaac-1's Avatar
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    Why the need for acid?

    Ok, this is one I have been wondering about for a while, what is it about swimming pool chemistry that tends to require the addition of acid to maintain pH. And more importantly why is there such a wide variation in the amount needed. I ask because my pool needs very little acid to maintain pH (around 1 quart per year of muriatic acid, although since it is so low I do tend to use dry acid instead for convenience) vs some pools that seem to need that much acid each day. My standard method of chlorinating is use of 6% bleach, plus very occasional use of dichlor when I also need to boost CYA (something under 5-10 pounds per year if I don't have a water leak). Any thoughts on why there is such variation, and is there anyone out there that uses no acid at all?

    Ike
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    Mod Squad jblizzle's Avatar
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    Re: Why the need for acid?

    Well the pH and TA of the fill water certainly has an impact. If the TA is high, pH will rise more. If there is a lot of aeration (spa, waterfall, SWG), pH will rise more.

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    JasonLion's Avatar
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    Re: Why the need for acid?

    I didn't use any acid at all last year, and about 1 pint the year before.

    PH drift varies dramatically with several factors, notably TA level, fill water TA level, and the amount of aeration the pool gets (which varies dramatically).
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Re: Why the need for acid?

    I have very low TA fill water, and keep my TA around 70 and have a chlorine generator. I havent had to add a drop of acid in 2 years. OTOH, I usually add 4-10 pounds of borax during the swim season to keep the pH from getting too low.
    14,000 gallon IG, Vinyl. Hayward 3/4 hp superpump, Penatair IC40 SWCG, Pentair automation, Hayward sand filter, Aqua Comfort heat pump, Hayward 400k Lo-Nox LP heater.

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    linen's Avatar
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    Re: Why the need for acid?

    I too use very little acid, just a little at the beginning of last season and I was good for the year.

    I would guess as the others have said, aerating water features (waterfalls, jets, etc.), swgs, and high TA, are factors that make the the acid demand seem higher then if you only looked at pools with no swgs, low TA, no aerating features.

    I sometimes wonder if "active swimmers" (I have a lot of splashy kids constantly using my precious pool ) also can cause a significant increase? Have not noticed it here though.

    Do you have borates in your pool?
    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: Why the need for acid?

    I have never had to use acid. For the first 6 or so years, I used trichlor, so that would explain those years. However, last year, for the first few weeks, I used trichlor, and then switched to bleach. Even with the bleach, I had to use some Borax. I don't have any aerating features, and the pool is not very active, so maybe that explains it. In fact, I am going to need some baking soda and borax when I open.
    John
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    Isaac-1's Avatar
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    Re: Why the need for acid?

    I have never used Borates, but my pool is indoors which changes a number of factors, lack of exposure to rain being one.

    Ike

    p.s. to add one more factor my water is from a private well
    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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    linen's Avatar
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    Re: Why the need for acid?

    Yeah, being indoors may also decrease your evaporation rate and therefore reduce the need for make up water. Many pool owners fill water (mine included) have high TA, which of course would require more acid to counteract.

    I also fill from a private well and my TA is typically in the upper 200s . This encourages me to keep my pool covered when practical.
    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: Why the need for acid?

    I add about a quart every 10 days or so and having been doing so since the pool was about 3 months old and it's now over 2 years old. It seems to be getting a little better. My TA is around 70 and I have a SWG but not much aeration. My fill water is high in TA so it's hard to get my TA low enough to stop the pH from rising.
    9,200 gal. Gunite Luna Quartz French Grey pool with spill over spa, two fountains on tanning ledge (rarely used)
    Pentair Whisperflo 2HP, Pentair CCP Cartridge 420 Sq. Ft., Polaris 280 with booster pump
    Pentair EasyTouch 4, RayPak LoNox 266k Natural Gas heater, Aqua Rite SWCG T Cell 9, Borates, TF-100 test kit

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    Re: Why the need for acid?

    My fill water TA has varied from 340 to 220 in two years. So whenever I add water, I will drive the TA up. With a spillover spa and a return on the swimout that breaks the surface constantly and worse when the water level drops just a bit, and evaporation losses from the big waterfall, my pH is always climbing. I normally consume something like 3 cups of acid at a time, twice a week I guess.
    23,000 gallon in ground pool with rock waterfall and spillover spa, Aqualink control system, Polaris 380 cleaner, Purex Triton Clean&Clear Plus cartridge filter. Located in The Woodlands, Texas.

    Pool owner since Nov 2008, Trouble Free since April 2009. Happy to help when I can.

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    ComputerGuyInNOLA's Avatar
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    Re: Why the need for acid?

    My TA is not high but I use a LOT of acid, to the tune of about 3 gallons per month. New plaster, SWCG, and waterfalls make it happen.
    Gunite/Plaster pool at 13k gallons. All Jandy with CL340 series cartridge filter, 1.5 HP Jandy Stealth pump. Jandy 1400 SWCG and PDA4 controller. Dual waterfalls. Polaris 280. Pool installed August 2012. Southern Louisiana. And lets not forget my trusty TF100 test kit!

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    Re: Why the need for acid?

    Just to note that there is another option to dealing with high TA and that is to operate a "high pH" pool instead of trying to lower the pH via acid. Ben Powell wrote about this in this link at PoolSolutions. You can't do this approach if you've got metals in the water and a pool surface that can stain and you can't use this approach if your water is high in Calcium Hardness (CH). Since oftentimes high TA and high CH go together in fill water, the high pH option isn't a good one for that situation. That's why we normally don't talk about it, but for those with a high TA but low CH and no metals, it's something to consider.

    Now, that said, one can at least minimize the amount of acid by targeting a somewhat higher pH and not going down as low. As shown in this chart, there's more carbon dioxide outgassing not only at higher TA, but also at lower pH.
    16,000 gallon outdoor in-ground 16'x32' plaster pool; Pentair Intelliflo VF pump; Pentair IntelliTouch i9+3s control system; Jandy CL-340 square foot cartridge filter
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