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Thread: Help with Alkalinity Adjustment on SWG Above Ground

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    Help with Alkalinity Adjustment on SWG Above Ground

    Hello All,

    I'm new here. However, I've spent a lot of time online recently reading about pool chemistry through various Web pages, how-to's, and forums. A member of another forum mentioned this one, so I thought I'd try my luck. I'd appreciate any help you can offer.

    We recently purchased an above ground that had been bought at a pool chain store and never installed (back in 2005). It was in boxes and new, so we proceeded with the purchase and installation. The local installers were the same ones that are used for the same retailer here in our area, although this pool was purchased out of town originally and the folks moved.

    The pool is a 18 X 33 buttressless Oval (I know the manufacturer but am not sure that I can post the name here). It has a wall height of 52". Our average depth is around 46". The first problem is that we've found varying calculators and formulas for determining volume. We have finally arrived at an estimated (nice round number) of 13,250 gallons at current fill depth, but I'm still not comfortable that this is correct. Some people have said our pool is 14,000 gallons and others have said 19,000 - big difference! Anyway, I have also not found anything that 100% clarifies that if 14,019 gallons, if this is assumably filled to the top of the wall or at average depth (how do these calcs work??). I think the total we finally went with was the book from our SWG and estimating around 3.85 feet as the average depth. Anyway, the pool has a sand filter with a "proclaimed" 2.5 HP motor - which I won't get into that, but from what I understand it is only a 1.5 HP.

    We have a SWG. The salt level is 3000 PPM.

    We are using a regents test kit that is OTO based for chlorine. Here are the levels:

    FC: 1.5
    TC: 1.5
    PH: 7.4
    TA: 190-200
    CYA: 50 (we added some to get here but have not added more yet)
    Hardness: N/A - have not tested due to vinyl pool

    I made the mistake with test strips of misinterpreting the TA and added 4 lbs of baking soda a week or so ago. We since got the regents kit and realized what had happened. TA was around 230. So, We've added Muriatic Acid twice now, which has brought it down some, but not nearly as much as expected. A couple of things might be going on - 1. water volume estimate wrong??? And / OR 2. Adding acid improperly.

    I read somewhere that to lower alk you have to add acid directly to the water to cause it to gas off the CO2. Is this correct? My concern is there is no "deep end" and this is a vinyl pool. So to make it safer to handle and to reduce the splatter, we mixed it with a bucket of water and poored it gingerly around various places on the perimeter of the pool away from the wall. So this is one major part of my question . . . are we doing this right?

    I noticed both times the PH came down a tad (from like 7.8 once to 7.4 and from 7.6 to 7.4) but we were very conservative in acid use. However the second time I used twice the acid (16 oz first then 32 oz next) and the change was about the same proportion. Also, after circulating the pool over 8 hours I noticed the ALK was still at 190, which is where it was approximately when we began the second time with the Acid (I think it was at around 200). So this began my concern about whether we are adding it properly or not.

    Finally, I know we need to add CYA - but I wanted to get the alkalinity right. My thinking is since we have a SWG and no other easy way to aerate the pool, I can let the SWG do the aeration. Right? I have read about dangers of Chlorine gas, but is it safe to circulate the pool say 4 hours on low and then turn on the SWG to do the aeration? The point about CYA is if we add more, then the chlorine will not dissipate as easily, thus hurting me on the need to run the SWG for aeration to get the ALK in control and PH back up. Incidentally, the SWG manufacturer suggests 80 PPM for CYA and I've also read that 90 PPM for ALK is best to reduce scaling with cell life on the SWG.

    Please help. I'm thinking we are close to a solution, but there are obviously a few important questions that are unanswered in my mind.

    Thanks!

  2. Back To Top    #2
    MikeInTN's Avatar
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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    Lowering your TA will take some time. Best I can remember from the last time I lowered mine (and am about to do so again), I'd add enough acid to lower the pH to around 7.2, and then aerate until the pH came up to around 7.6 or so, and then repeat. Every cycle my TA would drop by 10 ppm or thereabouts, I think.

    Diluting the acid is fine. Adding it full strength is fine too, as long as you add it slowly in front of a return or slowly drizzle it around the perimeter of the pool. You don't want to just dump it all in one place, as it will go straight to to the bottom and sit there until it dilutes, and can possibly harm your liner. Add enough acid to get down to around 7.2, and then aerate. The less acid you add (not taking the pH down to 7.2), the less the TA drops with each iteration.

    I wouldn't rely on the SWG for aeration. You can get fountains that hook up to your return and are great for aerating, or make one from PVC. Just search the threads, as some folks on here have made some dandy aerators from PVC. You can also adjust your return eye up to churn the water, which does a fairly good job, too.
    24' x 52" AGP - approx 13,500 gallons
    Pentair Optiflo 1 hp/2sp pump w/ Swimpro Voyager 150 sq ft cartridge filter
    Intex 8110 SWCG
    "Fear the Schnauz!"

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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    Wow thanks Mike. I didn't think about the return jet eye. Mine is a right angle, so it should work well being spun around. I'm going to give this a shot. We'll do CYA to 80 after we get ALK under control.

    Does anyone have any thoughts on the ACTUAL gallons in my pool? Is there a true formula I can rely on - and please clarify if you use total wall height or actual average depth when computing "average depth".

    Thanks!
    Daren

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    duraleigh's Avatar
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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    Hi, Daren,

    Welcome. There is a good article up in "pool school" (or linked in my sig) on lowering ALK.....it's the only way.

    Usually, you can figure an oval pool pretty close by taking both ends and combining them into a circle. Then what's left in the middle is an easy rectangle. Use the average depth of your water and that'll give you cubic feet. Then multiply by 7.50 and you should be pretty darn close.
    Dave S. - Forum owner
    42k vinyl and concrete pool, 1.5hp pump, 140gpm filter
    TFTestkits , PoolMath , Pool School

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    JasonLion's Avatar
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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    I get about 15,000 gallons with 3.85 feet deep water, more if you fill it to the top.

    You should go ahead and start adding the CYA. Without CYA you will be losing too much chlorine to sunlight.
    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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    MikeInTN's Avatar
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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    Hey Daren,

    Here's a thread that discusses aeration and pH. Click on the link in Poisedon's post about his homemade aerator to see a picture of it. Now THAT's an aerator!
    24' x 52" AGP - approx 13,500 gallons
    Pentair Optiflo 1 hp/2sp pump w/ Swimpro Voyager 150 sq ft cartridge filter
    Intex 8110 SWCG
    "Fear the Schnauz!"

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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    Wow . . . he has way too much time on his hands! That is awesome. Thanks for the info. We are in the process. TA is now at 170 as of yesterday, and I need to p/u some more MA today to start over.

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    frankthailand's Avatar
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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    Hello Daren
    This page might help with your pool volume.
    http://www.poolandspachemicals.co.uk/volcalc.htm

    Happy swims
    Frank
    Hello all from the land of smiles. Thailand. 5mx9mx1.5 63000L 16300 gall, pebbletex,
    pentair 1hp whisperflow, tagelus TA60 SF, swg monarch esc24 {a bit small for the tropics} 3 returns, 1 skimmer, 2 astral 100watt lights. Planned and built by me
    an AUSSIE expat living thailand for 18 years.

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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    Perfect; thanks! This fits inline with what we estimated or very close. I'll use this calc's info.

    Here's an update for those who have helped - We added MA yesterday again around 5PM. This time I didn't dilute it. I poured it gingerly around the return jet, but somewhat away from the wall. I was sure to fan it and use very little at a time in the tream. We added another maybe 20 ounces (I ran out). Today the PH was down to appx 7.1 from appx 7.3 yesterday roughly, but the TA was still showing at 170 as before the last add. So, I'm a bit confused.

    Anyway we have spun the jet upside down as suggested, and I'm aerating tonight for a few hours until bedtime and before switching the jet back around for the night cycle (will check it again in the morning and go back at it if PH is still low). I'm going to pick up some more acid and try again tomorrow.

  10. Back To Top    #10
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    Re: Help with Alkalinity Adjustment on SWG Above Ground

    This might be helpful to you. Be sure to check out the links if you want to know WHY it works and why slugging acid doesn't!
    viewtopic.php?t=5341

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