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Thread: Pool chemistry questions

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    Join Date
    Jun 2011
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    Pool chemistry questions

    Hello, I'm wanting to double-check what kind of chemicals I should add to my pool to bring it in balance. Here are my current readings:

    FC 5.5
    CC 0.5
    PH 7.8
    CYA 60
    Alk 140
    CH 125

    They may have gotten a little out of whack because of some recent event in my pool:

    1) I recently replumbed it, which took several days, causing it to sit stagnant for too long
    2) I wound up SLAMming it as a result, because of visible algae
    3) While topping off the pool, as the water was getting low, I accidentally left the hose on for about 4 hours which caused water waste, and some pool water wound up getting replaced with tap water in the process, as the pool was overflowing.

    So I can see my CYA dropped a bit, my PH went up, and the alkalinity also went up. Normally my PH rides to low, and I'm always adding washing soda, but now the PH is on the high side.

    Looking at pool math, it says that I should lower my alkalinity by adding acid and washing soda both, but it doesn't tell my how much acid to add. Well it does say to add enough to lower the PH to 7.0 to 7.2, but how can they make a blanket statement to that? Shouldn't somebody with slightly high alkalinity follow a different course than somebody with massively high alkalinity? Also, what ill effect does high alkalinity cause to my pool, by the way?

    Also, I've just installed a SWG, but haven't put it into service yet, but I think I should raise my CYA first. Do you think I should shoot for 80? I'm in a hot sunny climate (Austin, TX). I still have some chlorine pucks, so maybe I'll put some in the skimmer to boost the CYA. From one of my other threads:

    Quote Originally Posted by hyperionguy View Post
    For a 7,600 gallon pool each 3" puck (typically 8oz) adds 4.4 ppm CYA so use that to calculate how much you're adding so you don't over do it Remember that it takes up to a week to register on the test.
    So that suggest if I want to add 20 to my CYA, it'll take 4 1/2 pucks to do it. Maybe I'll throw in 4 pucks for now, and turn on the SWG once they dissolve, and a week later remeasure the CYA to make sure it's right.
    18 foot diameter, 52" tall above ground Cornelius pool, with vinyl liner, and resin wall caps.
    Roughly 7600 gallons
    Blue Wave "Sandman" Sand filter/pump, model NE6150. Pump is 1 HP
    Intex SWG, model # 54601E

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    pwrstrk's Avatar
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    Pool chemistry questions

    Don't sweat your TA. By keeping you PH in range, lowering it with acid when it rises, that will start to lower your TA. When you get your SWG going that will also raise your PH and lowering it with acid will keep lowering your TA. After awhile your TA will fall into a good spot.
    I would shoot for a CYA level of 70 at first. If your losing more than 2-3 ppm of FC to the sun then bump it up to 80. 😎
    Jeff
    24'x54" AG Morada RTR (by wilbar) 13'500 gal. Hayward Powerflo Matrix 1hp 2 speed. Hayward Perflex EC65 DE filter.

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    Re: Pool chemistry questions

    Quote Originally Posted by Zindar View Post
    Looking at pool math, it says that I should lower my alkalinity by adding acid and washing soda both, but it doesn't tell my how much acid to add. Well it does say to add enough to lower the PH to 7.0 to 7.2, but how can they make a blanket statement to that? Shouldn't somebody with slightly high alkalinity follow a different course than somebody with massively high alkalinity? Also, what ill effect does high alkalinity cause to my pool, by the way?
    Where do you see that PoolMath says that you add washing soda to lower the TA? PoolMath says the following in the TA section:

    To lower TA you reduce pH to 7.0-7.2 with acid and then aerate to increase pH.
    If you enter in your current pH under "Now" and put in 7.2 or 7.0 under "Target", then it will give you an estimate of how much acid you need to add (assuming you set the pool water volume in "Size" at the top and that you entered your current pH, TA, CYA and Borates in the "Now" column). If you have much higher TA then it will say you need to add more acid to lower the pH so PoolMath accounts for that. This is NOT a one-time procedure and the aeration causes the pH to rise so you add more acid to keep it low. Every time you add acid, the TA gets lowered. The procedure is described in the Pool School article on how to Lower Total Alkalinity.

    Though you just continue the procedure until you reach your TA target, in 7600 gallons every 19-1/2 fluid ounces of full-strength Muriatic Acid (31.45% Hydrochloric Acid) will lower the TA by 10 ppm. You can see this in PoolMath in the "Effects of adding chemicals" section.

    As Jeff mentioned in his post, you could alternatively just operate at your current TA and add acid to maintain the pH. Over time this will lower the TA level every time you add acid. The Lowering TA procedure just accelerates the process if you find the rate of pH rise to be too high and adding acid frequently to be too annoying.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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    Join Date
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    Re: Pool chemistry questions

    Oops.. you're right it says aeration instead of washing soda to raise the PH. In my mind, I was thinking washing soda, because if I understand correctly, aeration means pointing the jet to the surface, but when I do that, the lack of bottom circulation causes algae, even if I maintain the correct FC, so I've been using washing soda to raise the PH.

    But that's interesting if SWG's cause PH to naturally rise, so I'll try that and see how that works.
    18 foot diameter, 52" tall above ground Cornelius pool, with vinyl liner, and resin wall caps.
    Roughly 7600 gallons
    Blue Wave "Sandman" Sand filter/pump, model NE6150. Pump is 1 HP
    Intex SWG, model # 54601E

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    Join Date
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    Re: Pool chemistry questions

    During the procedure if you point up the returns you can raise your FC level to try and compensate for the poor bottom circulation.

    Note that using washing soda to raise pH also raises the TA since technically it's identical to adding lye (sodium hydroxide, a pure base) and baking soda (sodium bicarbonate). You might consider adding 20 Mule Team Borax to raise pH (when needed) since it will only increase the TA by about half the amount. However, when using a hypochlorite source of chlorine and especially for an SWG like you have the pH tends to rise so there should never be any need for a chemical to raise the pH.

    Note also that you definitely don't want to add either of these pH raising chemicals for the TA lowering procedure because they will completely undo what you are trying to do. In fact, the washing soda will end up increasing the TA in the procedure. The aeration is a critical part of the lowering TA procedure because it raises the pH with no change in TA.
    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
    12 Fafco solar panels; Purex Triton PowerMax 250 natural gas heater (200,000 BTU/hr output); automatic electric pool safety cover; 4-wheel pressure-side "The Pool Cleaner"

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