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Thread: pH at 7.8, added 1.5 cups of Acid, next day pH still at 7.8

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    pH at 7.8, added 1.5 cups of Acid, next day pH still at 7.8

    I don't know what is going on here, but my pH won't go down!

    It was around 7.8 and I did the acid demand test and it told me 1.5 cups, so I put that in, maybe even a tad more, and the next day, about 20 hours later, it is still at 7.8..

    What gives??

    TA is about 120ppm.. FC is about 2.5 or 3, CC is 0, CYA is like 0ppm, and CH is around 450.

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    JasonLion's Avatar
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    If you have fresh plaster or active aeration (SWG, waterfall, fountain, rain, etc) that isn't really that surprising. Any of those things will raise the PH back up fairly quickly. For causes other than fresh plaster, you can slow the PH increase by lowering your TA. Fresh plaster raises PH fairly rapidly for the first few weeks and more slowly for up to a year You might want to bring the PH all the way down to 7.2 when you lower it, that will give you a little more time between acid additions.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Also, check the strength of your Acid... around me (even at Lowes) I can only get 15%. Most of the charts in the test kits are written assuming 30% so you might only be adding half the dose you think you are.
    My Pool:
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    mas985's Avatar
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    How big is your pool? I know that 1.5 cups of acid in my pool would barely change the PH.
    Mark
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    My pool/spa is roughly 10000 gallons combined.

    I do have my pump which means aeration on 12 hours a day. I have two waterfalls which I will not turn off for the life of me - I love them too much!!

    So those two waterfalls (one's a spa spillway) are aerating THAT QUICKLY????

    I do have only 2 month old plaster but..

    I will for sure go down to 7.2 when I add acid next time.. good idea..

    But I had hoped higher TA levels would keep my pH steady.. And a few weeks ago it WAS steady but now it is moving up.. I'll keep an eye on it and adjust accordingly, but I can't wait until I don't have to keep dorking with my pH...

    Thanks,
    Kevin

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    I have found on my pool that I need to add twice or more of the quantity of acid as calculated by most pool calculators. There appears to be a "break" point. You need to add a certain amount of acid before the pH will move, and beyond that amount, the pH will change rapidly for small additional amounts of acid. In other words, for my pool 24 oz of acid will not change the pH but 32 oz will change it by 0.4 units.
    7,500 gal, IG pool, L shape 22' x 15', 1.5 hp pump, cartridge filter, AquaPlus SWG/Controller, Pebble-Tec liner.

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    but I can't wait until I don't have to keep dorking with my pH...
    Uh-Oh! maybe not the info your hoping for, Kev, but my non-SWG pool creeps up all summer and has for the past five years. Some pools will just do that and muriatic becomes a way of life.
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    JasonLion's Avatar
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    TA is strange. It both slows PH changes caused by the addition of acids or bases and it actually causes the PH to increase from aeration. With waterfalls running 12 hours a day the rate of PH increase from aeration can be significant. You can slow the rate of PH increase by lowering the TA. I would aim for TA around 60 because of the waterfalls. You can lower TA quickly now, or the regular addition of acid will do it for you slowly over the next several weeks.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Hmmm, well I know acid may be a way of life, but hopefully not more often than every 4-5 days.. Right??? RIGHT?!??!



    If the acid I just dumped in tonight (2.5 cups) doesn't get it back down to around 7.3, then I'm going to dump a bunch more in and see if that helps -- and helps lower my TA.

    I think what has happened is because my TA is now so high (120+) that my pH is impossible to move now.. Hopefully at least that is the case..

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    JasonLion's Avatar
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    It can take some fiddling to get your water to a point where the PH rise is very slow, but it can be done.

    2 1/2 cups of muriatic acid should have brought your PH down to right around 7.3 (and lowered TA by about 8), but PH is going to continue rising. The longer you wait before measuring again the higher the PH will be. As your TA comes down the rate of PH increase will also come down.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Ok, so the 2 cups I put in last night helped. My pH is down now to 7.5..

    So if 2 cups at high TA levels got me from 7.8 to 7.5, then 2 more cups will get me to 7.3, just a tad below perfect.. Which should be perfect for ME, because it can only go up with this much aeration, and at the high TA levels I have (120ish which I think is fine for my plaster pool), it will move slowly - or so it seems, so it should be 2 weeks before I'm up to 7.8 again.. If that is true, then I will continue this routine, as I think it is not too high maintenance, and still safe to use..

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    JasonLion's Avatar
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    Remember to test the PH regularly and adjust as needed. After you get a little more experience you will have a much better idea of what to expect and it will get much simpler. I suspect that the PH will be back up in three or four days but it could be soon or later depending on any number of things. The rate of PH increase will slow as the TA level comes down.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    Quote Originally Posted by JasonLion
    The rate of PH increase will slow as the TA level comes down.
    Don't you mean as the TA level comes up (or is high)?

    As I understand it, higher TA levels make it harder for pH to move, which makes sense as to why my pH is hard to fix/lower (because my TA is kind of high)..

    Also, is there any reason NOT to run higher TA levels (say 120+)??

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    JasonLion's Avatar
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    You should read my previous posts again. Your high TA levels combined with the aeration are causing the PH to increase. With all that aeration you want to have a lower TA level. If you raise the TA level any further your PH will rise so quickly that it will be difficult to keep under control.
    19K gal, vinyl, 1/2 HP WhisperFlo pump, 200 sqft cartridge filter, AutoPilot Digital SWG, Dolphin Dynamic cleaning robot
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    I think aeration aside the new plaster is going to cause the ph to rise dramatically. The first few months after my pool was done, I'd guess I put about 12 gallons of acid in there to keep the ph in range. Finally, 7-8 months later I'm now adding only a little every couple weeks.
    Gary
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    IPvFletch,

    TA is a measure mostly of the bicarbonate in the water and that is in essence a measure of the carbonation of the water. Yes, a pool is very much like a carbonated beverage. Carbonation is intentionally added to the pool (via sodium bicarbonate, or baking soda) in order to provide a pH buffer and for carbonates to protect plaster (along with calcium that is also added to protect plaster).

    Just as a carbonated beverage goes flat when you blow bubbles into it, so a pool also loses carbonation via aeration. This process makes the pH go up (because carbonic acid is removed from the pool for technical reasons I won't get into here) and then when you add acid to lower the pH, the TA gets lowered as well. The fact that a higher TA leads to a higher rise in pH and that a lower TA leads to a lower rise in pH is one of the most counterintuitive things in pool water chemistry, but it's true. It's simply that the effect of higher TA, and therefore higher carbonation of the water, causing outgassing of carbon dioxide which makes the pH rise is larger than the effect of the higher TA being a greater pH buffer.

    If you've never done this experiment as a kid, take some baking soda (or Alkalinity Up) in a cup or jar and add some vinegar to it (you can add some water to the baking soda first if you want to avoid a mess). Notice all the bubbles -- that's carbon dioxide. Vinegar is acetic acid so is acidic and adding that to baking soda which is sodium bicarbonate causes carbon dioxide to outgas. The same thing happens in a pool -- lower pH and aeration cause carbon dioxide to outgas faster.

    Just follow JasonLion's advice and lower your TA level and see what happens. If you add enough acid to have the pH be lower towards 7.0 (or even 7.2), then the outgassing will be even faster and the pH will rise more quickly thus accelerating the process of lowering the TA (assuming you continue to add acid as soon as the pH rises). It is the combination of aeration at low pH combined with acid addition that lowers the TA. Once you lower the TA to 80 or below, you should see a slower rise in pH and also a lot less acid that needs to be added over time.

    HOWEVER, new plaster makes the pH rise as part of the curing process and that may overwhelm what you do above (it's not that lowering the TA won't help, but you might not notice that much of a difference). As much as you love your waterfalls, you can just turn them off for a while (a few days) and see if it makes any difference in the rate of pH rise. As for the curing of plaster, that will taper off quickly -- the first month is really strong, then it's less for a few months, and after 6 months it'll be a lot less. After a year, you'll be close to where you'll end up though some report continued pH rise for a second year though not nearly as strong an effect.

    Richard
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